CGRO Cycle 4 Viewing Program: Abstracts

MONITORING THE GAMMA-RAY/RADIO STAR 2CG135+1/LSI 61 303

We propose a COMPTEL-EGRET Cycle 4 observation and BATSE monitoring of
the gamma-ray source 2CG 135+1. The main aim of the investigation is
to use high-energy data to confirm the association of 2CG 135+1 with
the radio-loud B-star GT 0236+610/LSI+61 303. This radio source is
known to have continuum radio emission modulated with a period P=26.5
days. Previous X-ray and gamma-ray observations of 2CG 135+1 could not
unambiguously confirm the existence of time variable high-energy
emission modulated with the radio period. We also plan to monitor the
source with radio observations and to carry out a theoretical
investigation based on Cycle 4 and previous GRO observations of 2CG
135+1. This source may be a prototypical example of a massive star
orbiting an energetic pulsar.  

Search for Gamma-ray Rmission from Starburst Galaxies NGC 253 and M51

We propose to observe the starburst galaxies NGC 253 and M51 for 4
weeks on each object with OSSE. The analysis of Phase 1 NGC 253 data
(total exposure 8 x 5^5 detector s) showed a positive excess with a
significance of 4.2 sigma in low energy region. The Phase 2 and 3
combined OSSE exposure is only 2.4 x10^5 s and not enough to ascertain
whether the excess emmision detected during Phase 1 originated from
NGC 253; the detection of gamma-ray emission from this galaxy has
important implications for starburst models. M51 is an another nearby
infrared bright galaxy which has been seen by Ginga satellite in X-ray
energies. The extrapolated Ginga x-ray fluxes have higher values than
the OSSE 1 sigma sensitivity limits. The possible existence of a low
luminosity AGN and a recent supernova in this galaxy make M51 an
attractive target.  

MORPHOLOGICAL STUDIES OF SHORT GAMMA RAY BURSTS

GRB's of duration < 2 s which presumably form a separate class, are
proposed to be studied using the BATSE very high time resolution data
in different energy bands (viz. TTE data).  Only a subset of short
GRB's for which a complete TTE data set is available qualify for this
study.  Such a study is already underway and a sample of 37 such GRB's
have been studied so far.  Some very interesting correlations have
been observed and reported.  For example, short bursts with more
complex time profiles are likely to exhibit a higher spectral
hardness.  In order to confirm these results we need to study more
such bursts from the available BATSE database.  In addition, a
systematic search for milli-sec/sub- milli-sec features in GRB time
profiles is also in progress.  These studies can potentially lead to
an understanding of the origin of short GRB's.  

Gamma-ray burst model constraints imposed by 8ATSE observations

Models of gamma-ray burst spatial distributions and luminosity
funnctions will be generated, analyzed, and compared to BATSE angular
and intensity distributions as part of an ongoing investigation.
Special attention will be given to updating the ways in which
observational selection effects are modeled.  AnaIysis techniques will
be refined to make more use of angular/intensity information provided
by the increasing number of BATSE bursts.  Studies will concentrate on
cosmological models: in particular on constraints imposed by (1)
anisotropies such as the Local Supercluster, and (2) epoch evolution
of source luminosities.  However, more local models will continue to
be studied as the need arises.

This project is Requests for Observing Time (Type 2) requiring high
level processed data (data type 2) pertaining to burst peak fluxes,
locations, and subclassification parameters (hardnesses, etc), as well
as BATSE skymaps.  

DIFFUSE GAMMA-EAY EMISSION AT HIGH LATITUDES

At high galactic latitudes a significant faction of the diffuse
gamma-ray emission is believed to be extragalactic. The uncertainties
in the measurement of this emission are due to the residual emission
from the galactic disk and the lack of knowledge about the existence
of a galactic halo component. Using EGRET archival data, we will study
the correlation of gamma ray intensity with matter with the aim of
separating the gamma ray component originating outside the galactic
disk.  Galactic halo emission will be studied using the latitude
dependence of the gamma ray emission. We also propose an EGRET
observation of the Lockman H I hole and Loop III regions.  Additional
observations of these regions of known low gas density will allow a
more accurate deteimination of the spectrum of extragalactic gamma ray
emission than is currently possible, providing a significant
improvement in our understanding of diffuse extragalactic gamma rays.

Determining the Characteristics of Solar MicroMares

We are proposing to continue an ongoing automated effort to find and
catalog solar microflares in the BATSE data.  We propose to extend the
research into longer time scale phenomena with the larger data base
and to correlate the microflare events and event rate with
observations at other wavelengths. The BATSE LADs allow for the most
sensitive, long term study of microflares ever conducted. Microflares
have been proposed as the basic component of solar flares and as a
source for heating the solar corona. This effort seeks to determine
the importance of microflares in these physical processes and to
expand the flare search and catalog into more phases of the solar
cycle. A long term study opens up numerous possibilities for
sophisticated statistical studies of microflaring rates as functions
of many solar parameters. This study improves upon earlier work by
Schwartz et a]. (1992) because of the greater number of microflares
detected in a computer search of BATSE data.  

Gamma-Ray Burst Angular Distribution Studies with COMPTEL

We propose to study the angular distribution of gamma-ray bursts using
data from the Imaging Compton Telescope (COMPTEL). COMPTEL's superior
burst location capabilities allow us to search for evidence of burst
recurrence and spatial clustering on small angular scales with high
sensitivity even though the total number of bursts is limited. The
primary tools to be applied to the full COMPTEL burst data set are the
two-point angular correlation function and the nearest neighbor
distribution function.  These tools applied to COhIPTEL data could be
decisive in providing a convincing answer to the fundamental question
of whether bursts repeat or not. We request data rights for all
gamma-ray bursts in the COMPTEL field of view and funding for this
research.  

A Rapid Response Gamma Ray Burst Detection Network Based on COMPTEL
Localizations

This is a COMPTEL Type 3 proposal to search on real-time notice for
optical and radio counterparts to cosmic gamma-ray bursts. We request
data rights for large gamma-ray bursts in the COMPTEL
field-of-view. We also request funding for logistical and scientific
support for the ground-based observer network organized and
coordinated by New Mexico State University. Using a procedure
developed and improved over the last three years of Compton
Observatory operations, we can now produce in ~1 hour locations and
relatively small error boxes (+/-1 deg) of large gamma-ray bursts
which occur in the COMPTEL field-of-view. Error boxes of this size
enable optical and radio observatories to conduct productive quick
searches for gamma-ray burst counterparts. Work in progress promises
locations on the time scale of 10 - 20 minutes. A ground based network
coordinated by NMSU of willing and capable observers now exists to
participate in such an effort. Searches of this magnitude and speed
open up a whole new time domain in the gamma-ray burst counterpart
search problem. This gamma-ray burst counterpart search complements
the work of the BACODlNE experiment.  Support is provided by the
BACODINE and Interplanetary Network experiments. Given that we know so
little about the nature of gamma-ray bursts, such searches may provide
one of the best 0pportunities to solve the gamma-ray burst riddle.

Studies of X-Ray Binary Systems with EGRET

We propose to use EGRET measurements to search for gamma-ray emission
from selected x-ray binary (XRB) systems. There are many reasons, both
theoretical and observational, to suspect that some XRBs generate
outbursts of gamma-rays with energies in the EGRET energy band. Many
theoretical models predict fluxes that should be detectable with
EGRET, but the predictions are often sensitive to model parameters
that are presently unconstrained by observations. Interpretation of
the EGRET measurements will allow us to place important constraints on
models for high-energy processes in XRBs. We present a program to
search for 35 MeV-30 GeV emission which complements the on-going
COMPTEL team studies of XRBs at energies below 30 MeV.  

Steps Toward Positive Identification of High-Latitude Gamma-Ray
Sources

The majority of EGRET high-latitude sources do NOT have POSITIVE
IDENTIFICATIONS, which are vital for almost any further progress in
understanding them. We propose further observations of the most
promising 20 such sources to decrease the sizes of their error
circles, greatly facilitating our searches for identifications at
lower frequencies; obtain better information on their gamma-ray
variations and spectral slopes, which can for example distinguish
blazars from pulsars; and search Òtentatively identifiedÓ blazars for
correlated variability in the gamma-rays and lower frequencies. In
addition to improving substantially the number of positively
identified gamma-ray sources, our observations will also provide
further information about the nature of the unidentified sources,
including how they may differ physically from previously detected
blazars.  

Fractal and Wavelet InvestigationS of Burst and Transient Data

We propose to analyze the time profiles for Gamma Ray Bursts and other
transient data. Previous work has focused on fitting fundamental pulse
shapes, quantitative measures of spikiness and Fourier Analysis. We
propose to examine a large number of data sets using fractal and
wavelet analysis which provide quantitative measure of variability and
also give power as a function of time. These data sets will include
strong bursts, X-ray Binary data, and solar flare data. The results of
the search will hopefully serve to constrain the wide ranging models
for GRB emission processes and the dynamics of accretion for XRB, as
well as supply a set of widely applicable tools for analysis of
complex, nonstationary data sets.  

EGRET TIMING OF GEMINGA BASED ON HST HIGH RESOLUTION IMAGING.

The identification of Geminga as a rotating NS led to the discovery of
its proper motion. During EGRET observations this must be taken into
account, especially for accurate timing.  It can be shown that an
error of .1 arcsec reflects in a .4 msec timing uncertainty, so that,
over the life of GRO, already a shift of about one bin is introduced
in its 100-bin light curve.  We have extremely accurate positions for
Nov 92, Jan 94 (ground based, NTT, error .1 arcsec), march 19, 1994
(HST observation, error .05 arcsec), sept 94 and march 95 (HST
approved).  We propose to perform contemporary EGRET/HST observations
of Geminga in sept 94 and march 95, plus timing on archival data, so
as to obtain a meaningful measurement of Geminga's second period
derivative, of key astrohysical significance.  

The hard X-ray spectrum of the obscured Seyfert galaxies NCC 5506 and
NGC 4388

In the Unified Schemes, the nuclei of Seyfert 2 galaxies can be
directly seen only at energies where the obscuring torus becomes
optically thin, i.e. in the hard X-rays.  We propose to observe two
bright, soft X-ray obscured Seyfert galaxies, NGC 5506 and NGC 4388,
in order to test whether the nuclear spectrum of Seyfert 2s is equal
to that of Seyfert 1s, as expected in the unification hypothesis The
first of these objects one of the brightest Seyfert galaxies in the
2-10 keV X-rays, has not yet been observed by OSSE.  The expected good
signal to noise ratio should permit to also study whether the X-ray
spectrum is thermal or not in origin, and to study the contributions
of the Compton reflection components from both the accretion disk and
the obscuring torus. To these purpose, simultaneous observations at
lower energies are invaluable in tightly costraining the spectral
shape. We will therefore propose ASCA observations of both sources for
the next (AO3) cycle.  

0SSE Observations of Be binaries

We propose to observe three Be binaries with OSSE which are
sufficiently bright and have sufficiently hard spectra. The goal of
these observations is to confirm a correlation between pulse period
and spectral shape which we have found in A4 and BATSE data. We
suggest to observe the two sources with the hardest spectra, X Per and
GX 304-1, and another source, GS 0834-430, during one of its recurrent
outbursts.  

BATSE OBSERVATIONS OF SEYFERT II GALAXIES

We propose to study a selected sample of Seyfert II galaxies using the
BATSE instrument aboard the Compton Observatory. We intend to exploit
the Earth occultation technique applied to the LAD data to search for
emission in the 20-00 keV band from this class of objects. According
to the AGN unified schemes, Seyfert II are Seyfert I nuclei hidden
behind an obscured torus of dust and gas.  Measurements in the BATSE
energy range, where the opacity of the blocking material is low,
should allow us to observe the nucleus behind the torus and compare it
to that of a Seyfert I. The observed and gamma-ray spectral
characteristics of Seyfert II galaxies can then be compared to the
model predictions in order to test the unified model of AGNs. A study
of the X/ gamma properties of Seyfert II will also be very useful to
define their contribution to the Cosmic Diffuse Background Radiation.

OSSE OBSERVATIONS OF 3C 109 and NGC 7172

We propose to observe with OSSE two bright gamma-ray emitting active
galaxies, namely 3C 109 and NGC 7172, which have not been scheduled
for observations up to now.  Both objects belong to the class of
highly obscured type II AGN: one (NGC 7172) represents an example of a
nearby and the other (3C 109) a faraway type II source.  In
particular, 3C 109 could well be the first absorbed QSO observed at
high energies.  Both objects are bright enough to be detectable by
OSSE in a standard observation time.  Goal of the proposal is to study
the spectral characteristics of the two ob- jects at gamma-ray
energies and to compare them with the well known soft X-ray behaviour.

COMPTEL Observations of selected AGN at MeV Energies

It is proposed to continue COMPTEL observations (O.5 -30 MeV) of five
sources (one source has two potential counterparts) from which
definite MeV-emission has been detected previously. Four of the
sources are bright blazar-type AGN which have been discovered
originally in gamma-rays by EGRET. The other source is an unidentified
object, presumably an AGN as well. It is only seen by COMPTEL, not by
EGRET.  The objectives of these observations are I) to measure the
spectral shape, especially the spectral breaks occuring at
Mev-energies, 2) to determine possible correlations between source
intensity and spectra by comparison with previous measurements, 3) to
determine the duty cycles of high intensity states, to search for
further, previously undetected MeV-sources using the additional
exposure collected in these sky regions, to estimate the contributions
of unresolved AGN to the diffuse background radiation, and G) to
participate in multiwavelength campaigns on blazars.  

The Gamma-Ray Luminosity Function of Radio Pulsars

Only five rotation-powered neutron stars have been detected at
energies above100 MeV and many questions concerning the efficiencies,
beaming factors, and evolution of these gamma-ray pulsars remain
unanswered.  As a consequence, their contribution to the gamma-ray
luminosity of the GaIaxy remains uncertain by a factor of 30. We have
developed a formalism which uses the detection and nondetection of
radio pulsars in gamma-ray surveys in order to constrain these
parameters.  We propose here to conduct a deep survey of the region of
the Galactic plane which is maximally effective for the purpose of
determining the gamma-ray luminosity function of radio pulsars.

Echoes in X-ray Novae

We propose to use OSSE in a Target of Opportunity (ToO) to study the
secondary and tertiary maxima of soft x-ray transients (SXTs) that are
likely to be detected by BATSE during Compton cycle 4. It has been
noted recently that the presence of secondary maxima in the light
curves of SXTs may provide important information on the emission
mechanisms (Chen, Livio, Gehrels 1993). Two alternative models have
been proposed to explain the existence of secondary maxima (CLG;
Augusteijn, Kuulkers, and Sheaam 1993). These models make definite
predictions about the wavelength dependent light curves for successive
emission maxima.  OSSE has sufficient sensitivity to make detailed
light curves of the secondary and tertiary outbursts of the SXTs in a
few energy bands.  The proposed observations would permit detailed
comparison of the transient emission with the theoretical models and
should significantly advance our understanding of the emission
mechanisms of x-ray novae.
        

Gamma Ray Observations of the Interstellar Clouds in Cepheus

The interstellar clouds in the Cepheus and Polaris flares comprise one
of only a few cloud complexes that can be studied in detail with
EGRET.  Study of the high energy, diffuse gamma ray emission detected
by EGRET together with radio and millimeter surveys of the
interstellar gas will permit the determination of the cosmic ray
density and perhaps the electron/proton ratio as well as the
N(H2)/W(CO) molecular mass-calibrating ratio in this complex.
Previous work suggests that these quantities may vary significantly in
Cepheus/Polaris.  These variations, important for the physics of
cosmic-ray acceleration models and molecular clouds, could be studied
with improved exposure.  

OSSE OBSERVATIONS OF X-RAY SELECTED SEYFERT GALAXIES

We propose OSSE observations of the Seyfert 1 galaxies NGC 3227 and
III Zw 2, from the sample of hard X-ray sources of Piccinotti et
al. (1982).  Recent Ginga measurements show they are among the
brightest Type 1 Seyferts in that sample which have not yet been
adequately observed with OSSE.  Seyfert 1 galaxies are the most common
class of AGN detected by OSSE (Johnson et al. 1994).  OSSE
measurements indicate most have spectral cutoffs around 50 keV, while
IC 4329A has a much higher cutoff.  Refining gamma ray spectral
measurements of Seyferts, to discriminate between various AGN models,
can be achieved by using the combined measurements of a sample of
galaxies.  Coordinated Asca observations at lower energies will also
assist in the testing of AGN models.  

IDENTIFICATION OF SOUTHERN, HIGH-LATITUDE EGRET SOURCES

We propose to identify 19 serendipitous, southern, high-latitude EGRET
sources with optical counterparts via a combined radio and optical
approach.  Together with parallel work we are pursuing in the north,
this work has the potential to double the number of detected EGRET
quasars and BL Lacs.  We will use new and soon-to-be released southern
radio data (both fluxes and spectral indices), combined with
likelihood ratio techniques, to reduce the number of catalogued radio
counterparts per EGRET field from ~11 to 2-3.  We will perform the
entire follow-up optical spectroscopy in 8 nights.  We bring to this
work our pooled experience in southern radio observations,
serendipitous X-ray source identifications, and EGRET data.  

TeV Extension of the First CGRO EGRET Source Catalog

More than 100 sources have been detected by EGRET, most of which are
not identified; for many of these there is no information at all about
the energy spectrum above 30 GeV. To extend the energy spectra to
higher energies ground-based atmospheric Cherenkov telescopes must be
used.  The most sensitive telescopes in the 200-10,000 GeV range are
those presently operated by the Whipple Observatory Gamma Ray
Collaboration. Observations on some 25 EGRET-detected sources in the
past three years have thus far resulted in two solid detections (the
Crab Nebula and Markarian 421) by the Whipple Collaboration; the
collaboration is in an excellent position to extend their observing
program to all the sources in the ECRET Catalog that can be viewed
from the Whipple site (down to declinations above -20¡.  The
usefulness of the EGRET catalog will be enhanced by a complementary
catalog of fluxes (and upper limits) at energies of 0.2 to 10 TeV.

Gamma Ray Observation of Supernova Remnants

TeV gamma-ray astronomy is an important window for the exploration of
supernova remnants and their role in the acceleration of cosmic ray
particles. Since photons of energy of 1 Tev or greater are almost
inevitably the product of the interaction of a progenitor particle of
even greater energy, the observation of sources of TeV gamma rays is
the direct observation of sources of cosmic rays (hadrons or leptons).
Of the three well-established sources of TeV gamma rays (the Crab
Nebula, P5Rl706-44, and Markarian 421), two are pulsar-driven
supernova remnants. The Whipple Observatory Gamma Ray telescopes which
operate in the 100-1000 GeV range will be used in this study.  

Solving the Riddle of the Galactic Center Gamma-Ray Source.

EGRET has detected a strong point-source-compatible emission excess at
1=0, b=0, which shows strong indication for time variability. This
proposal aims for solving the question of variability in order to
decide for one of the two general interpretation scenarios: either the
origin as - steady - enhanced diffuse emission from within l00 Pc from
the galactic center, or - in the case of variability - the origin in a
compact object located within 0.2 degrees from the center of the
Galaxy.  A 2 to 4 week observation of the galactic center region is
proposed.  In the proposed observation also numerous other interesting
galactic targets can be observed by the GRO instruments.

Investigation of the High Latitude Diffuse Gamma-Ray Emission

The Energetic Gamma-Ray Experiment Telescope (EGRET) offers the only
opportunity for the foreseeable future to investigate the high
latitude diffuse gamma-ray emission at high energies.  The aim is to
separate relative contributions from a truly diffuse origin and those
due to unresolved discrete sources.  With ever increasing space debris
and artificial background radiation, the minimum mass design of EGRET
may be the best opportunity to determine the nature of this presumably
extragalactic diffuse component of the celestial gamma-radiation. The
proposed program aims to make the best possible estimate of the
extragalactic flux and spectrum, to examine the spatial fluctuations
in the emission and to study possible origins of the radiation.  A
deep exposure of eight weeks is proposed for two regions, one at
northern galactic latitudes in the Virgo region (1 = 290, b = 71) and
one at intermediate southern latitudes in the region of the large
Magellanic Cloud (LMC) (1 = 275, b = -34).  Four of the eight weeks on
Virgo is already credited from our phase 3 proposal. These viewing
directions are chosen to meet the objectives of this proposaI while
complementing other proposals by the EGRET team for a deep survey of
AGN, multiwavelength observations of AGN, and a deep observation of
the LMC.  

STUDIES OF HIGH-ENERGY PULSARS WITH EGRET

The Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton
Gamma Ray Observatory has detected five isolated pulsars, found
possible pulsed emission from another, and obtained upper limits on
many others. PSR B1706Ñ44 and PSR B1055Ñ52 gamma-ray studies remain
limited by available EGRET statistics, as is the case for the sixth
candidate, PSR B0355+54.  Additional data are essential to compare the
properties of these pulsars to those of the brighter ones. For the
Crab, Vela, and Geminga pulsars, additional observations will help
theoretical models interpret the geometry and physics of the neutron
star magnetosphere. These three have all shown indications of time
variability, which can he tested by continued monitoring, and all are
important calibration sources for the EGRET instrument
performance. For all except Geminga, contemporaneous radio timing
observations are needed.  

ANALYSIS OF GAMMA-RAY BURSTS DETECTED BY EGRET

EGRET detects approximately two gamma-ray bursts per year; however,
the results from these few bursts have been astounding. Thirty MeV to
greater than a GeV emission has been observed to last as long or
longer than the emission observed by BATSE. In GRB940217, high energy
emission is observed in the next orbit Ñ over an hour after the BATSE
detection, and the highest energy gamma ray was over 20 GeV¥ Also,
EGRET has collected spectra in the energy range of 1 MeV to 100 MeV
that have been combined with observations from other instruments to
yield spectra spanning up to four orders of magnitude in energy. We
propose to continue analyzing the data from the gamma ray bursts in
Cycle 4.  

Investigation of Energetic Solar Flare Processes Using the Sigh Energy
Capabilities of EGRET

The high energy capabilities of the EGRET instrument provide an
opportunity to investigate energetic solar flare processes. During the
June 1991 solar target of opportunity EGRET obtained spectral and
temporal measurements of high energy gamma ray emissions up to 1 GeV,
lasting hours after the impulsive phase of the flare. The spark
chamber telescope imaged gamma rays above 30 MeV and the NaI
spectrometer Total Absorption Shower Counter (TASC) observed spectra
in the energy band from 1 to 200 MeV. The TASC data provided line
fluences especially of 2.2 and 4 MeV, and also showed evidence of
delayed emission that is due, in part, to solar neutron emission. The
observations provide information on the spectrum of energetic
electrons and protons at the Sun, and on the details of their
interactions and confinement. We propose to analyze all CGRO Phase 4
solar flares that occur within the EGRET spark chamber field-of-view
to search for high energy emissions. Also, we propose to investigate
both gamma and neutron flare emission using the omni-directional TASC
detector with proven modeling analyses for background correction and
propagation through the spacecraft.  

Search for Untriggered BATSE Gamma-Ray Bursts

We propose to continue our search of BATSE continuous medium
energy-resolution data for bursts which did not generate an on-board
trigger. This program takes advantage of a realistic, physically based
background model that has already been developed and is undergoing
continuous improvement at JPL under a separate BATSE Earth Occultation
Guest Investigation. The technique searches residual counts above the
fitted model and offers better sensitivity than searching the raw
data. During Cycle 4, we propose to improve the search algorithms and
extend the analysis to approximately I year of BATSE data. During the
first half of the Phase 3 investigation, we have validated our
original estimate of sensitivity and identified several untriggered
gamma-ray bursts.  

Unidentified or Questionable High-Latitude EGRET Sources

The EGRET catalog of point sources detected in Phase 1 includes 38
identified AGNs and 43 unidentified sources with (|b| > 10¡. Of the
identified sources, nine have positions outside their 95% confidence
error boxes. This has a probability of 10^-4 of occurring because of
statistical fluctuations. Most of these nine sources are in regions
which have been observed only at the periphery of EGRET's field of
view. Thus their derived positions may be influenced by systematic
errors, and more direct observations could be beneficial. We also
propose to observe seven of the unidentified sources as part of a
multiwavelength campaign to search for timing or spectral
characteristics that could lead to identification with counterparts at
other wavelengths.

Investigation of High Energy Gamma-Ray Emission from AGNS: Deep Survey
Observations at High Galactic Latitudes

Deep exposure EGRET observations of the Virgo region (4 weeks) and of
thc LMC region (8 weeks) are proposed.  These exposures, combined with
previous observations of the same regions, will allow better
determination of the duty cycle and variability time-scale of the
gammaÑray emission, the spectra, the redshift distribution, the
logN-logS distribution, etc. of gamma-ray emitting active galactic
nuclei (AGNs).  These data are also important for evaluating the
contribution of AGNs to the diffuse extragalactic gamma-ray
emission. The value of the gamma-ray data will be greally enhanced by
contemporaneous multiwavelength observations of selected AGNs in the
EGRET field-of-view.  Planned coverage includes X-ray observations
with ASCA and ROSAT, UV observations with IUE, and ground-based
observations in TeV gamma rays, optical, mm-submillimeter, radio, and
VLBI. These multiwavelength studies will contribute to understanding
the high energy gamma-ray emission mechanisms in these sources.

STUDY OF HIGH-ENERGY FLARE NEUTRONS AND GAMMA RAYS USING THE EGRET/TASC

The EGRET instrument has identified high-energy signals from neutrons
and gamma-rays in solar flares from the June 1991 active region 6659
on June 4 and June 11 and possibly on June 6 and June 9 (Bertsch et
at.  1994). Previously the EGRET team has reported the detection of
high-energy rays (< 10 MeV) from these and other flares which in two
cases extend to GeV energies (Kanbach et al. 1993; Schneid et al.
1994; Dingus et al. 1994), but the neutron spectrum has not yet been
determined. The purpose of the proposed program is to confirm the
EGRET report and determine the spectrum of neutrons at the Sun, the
associated meson-decay gamma-rays for the full event and estimate the
flare proton spectrum. This program will extend the flare neutron
observations to >200 MeV which is not possible with other CGRO
instruments.  

JOINT CGRO OSSE - ASCA OBSERVATIONS OF THE BRIGHT SEYFERT 1 GALAXY IC 4329A

We propose a 4-week OSSE observation of the bright Seyfert 1 galaxy IC
4329A, to be conducted in January - February 1995 simultaneously with
Asca. This object is the second brightest radio quiet Seyfert galaxy
in hard x-rays, but it is more representative of Seyfert 1's in
general than the brightest one, NGC 4151. The observation proposed
here, together with simultaneous Asca data, will provide first truly
simultaneous data set sensitive to the onset and high energy end of
the Compton hump. The added sensitivity afforded by the new data in
the 180-360 keY range - at the expected energy of the downscattered
annihilation line - will allow us to conclusively reject the
non-thermal models for AGN.  

AGN UNIFICATION MODELS: SIMULTANEOUS ASCA AND GRO OBSERVATIONS OF MRK 3

We propose to observe the bright Seyfert 2 galaxy Mrk 3 simultaneously
with CGRO/OSSE and ASCA. Previous X-ray observations indicate that
this source should be bright in the OSSE band.  These observations
will clarify the nature of the high energy continuum in this source
and provide information on the origin of the intense iron K-alpha
emission line. Unification models predict the central source in
Seyfert 2 galaxies to be the same as that in Seyfert 1s, and we intend
to test this hypothesis. Our chosen observing strategy with ASCA
allows us to probe variability with both satellites on timescales of
days to weeks, providing the tightest possible constralnts on
unifications models.  

 
JOINT GRO-ROSAT-ASCA STUDIES OF EGRET OVV OUASAR5

OVV quasars (blazars) detected by EGRET have gamma-ray spectra which
can be locally approximated by power-laws with photon indices ranging
from 1.7 to 2.6, and luminosities which are (in E F(E)) 1-2 orders of
magnitude higher than the X-ray luminosities. In the case of two
objects, CTA 102 and PKS 0528+134, the connection between the X-ray
fluxes and gamma-ray spectra is the most extreme, requiring a sharp
spectral break, with change of index 1; the presence of such a break
severely tests all theoretical models. However, the X-ray and
gamma-ray observations of these highly variable sources were not
simultaneous, and thus the presence of the break may be just an
artifact of measurements at different epochs. We propose joint CGRO
EGRET, ROSAT HRI, and Asca observations of these 2 sources.  

OSSE OBSERVATIONS OF THE CLUSTER A2319

Measurements with the OSSE detectors aboard the Compton satellite can
lead to an important new discovery: detection of diffuse high energy
X-ray emission from clusters of galaxies. We propose OSSE measurements
of A2319, an AbeIl cluster with known extended (`halo') radio
emission. A23l9 and Coma are the only two radio halo clusters which
have been previously detected at energies ~30 keV by the HEAO-I A4
experiment. A two-week OSSE measurement will either result in
detection, or in an improved upper limit on emission at energies > 46
keV. Detection of A23l9 will not only establish clusters as the
largest high energy X-ray sources, but will also pave the way for
important investigations of their nonthermal properties. Specifically,
such a detection will enable a direct determination of the mean
magnetic field and energy density of cosmic ray electrons in the
intracluster space based only on observables.  

STUDIES OF BATSE TRANSIENTS AND BLACK HOLE x-RAY BINARIES

We propose to study black hole transients With BATSE using both the
occultation and imaging techniques. Our goals are to study historical
transients to search for low level outbursts and spectral features and
to search for new faint transients in the same fields.  Using selected
archival data, we expect to discover several new faint transients and
to constrain models for black hole sources.  We shall carry out
correlative optical and x-ray studies of historical and current (Cycle
4) transients and compare black hole vs. neutron star transients to
derive constraints on the total populations of each in the Galaxy.

STUDY OF THE S0FT GAMMA-RAY REPEATERS

We propose an in-depth study of the Soft Gamma Repeaters (SGR) through
a combination of spectral data analysis, archival data search, new
observations, and theoretical modeling.  We propose to extend the
hardness ratio versus fluence plots of the ICE and KONUS bursts by
including the new BATSE results to determine if there is any
dependence of the spectral shape on burst fluence.  We will use the
BATSE Earth occultation technique to try to observe the steady
emission of gamma rays from the plerion G10.0Ñ0.3 for the first time;
this is believed to be the counterpart of SGR 1806Ñ20.  We also
propose to assist in searching the BATSE database for sub-trigger
SGR-like events.  Theoretically, we propose to continue our
development of models for the SGR emission and particle energization
mechanisms. In particular, we are investigating whether Compton
scattering, cooling electron synchrotron radiation, and photoelectric
absorption are important for the formation of SGR spectra.  

 
BATSE STUDY OF KARD X-RAY EMISSION FROM BURSTERS

We propose to study x-ray bursters with BATSE using both the
occultation and imaging techniques. Our goals are to study >-ray
binaries containiling neutron stars to measure or constrain the
underlying hard x-ray spectra recently discovered by SlGMA.  We shall
analyze archival and Cycle 4 data on 8 bursters selected for their
likelihood of hard emission in order to test whether NS systems are
indeed different from BH binaries and to test models for both
non-thermal and thermal hard x-ray emission.  We propose theoretical
work to clarify the mechanism of hard x-ray emission from accreting NS
systems and to model the hard x-ray variability.

Search for Hard x-Ray Emission from Aquila X-1

We propose to search for hard x-rav emission from the recurrent x-ray
transient Aquila X-l in the BATSE database using Earth occultation.
This source, as an x-rav burster, is a potential source of hard x-ray
emission similar to other bursters such as GX 354+0.  We wish to
perform a characterization of its hard x-ray light curve and spectrum,
and correlate this with repeated optical outbursts (1991-present) as
reported in the literature.  This source is potentially interestinq
from the point of view of understanding the hard x-ray- emission from
neutron star as well as black hole systems 

PERIASTRON OBSERVATIQRS OF A0535+26 = GRO J0542+26

Although it has long been known that a positional coincidence exists
between the high energy gamma-ray source GRO J0542+26 and the
transient Be X-ray binary A0535+26, previous attempts to establish the
identification have been inconclusive. Rscently, A0535+26 has again
become active, and outbursts have been detected by BATSE during the
last four periastron passages, leading to the determination of precise
orbital elements.  However no EGRET observations have occurred (or are
scheduled) during these outburst times. We propose EGRET and BATSE
observations of the high energy gamma-ray source at a future
periastrcn massage of the hard X-ray source, in an attempt to detect
the characteristic 104 pulsations and/or (anti-)correlated variability
which would establish the identification. If confirmed, this would be
the only source which changes states between accretion-driven X-ray
enission and spin-poweered high-energy gamma-ray emission.  

BATSE Observation of the Flat X-Ray Spectrum Quasar PG1416-129

We propose to search for the hard x-ray emission from the quasar PG
1416-129 with BATSE instrument. Of all active galactic nuclei observed
with GINGA this source has exhibited the by far flattest X-ray
spectrum in the range 2-20 keY, with an energy index of 0.10 (+0.11,
-0.10). If this spectrum (with its 2-10 keY flux typically 1/15 of
that of 3C 273) continues without a break into the BATSE energy range,
BATSE has the required sensitivity to measure it. An OSSE observation
of this source is planned in Phase 3 (VP 339), proposed by the Co-I
(Staubert). By combining BATSE and OSSE data together, we can observe
the spectral behaviour for this source from 20-300 keV with BATSE and
50Ñ1000 keV with OSSE and the possible time variability with BATSE's
continuous coverage since April 1991. This is of great importance for
models of active galactic nuclei in general and is relevant to the
question of which type of objects is contributing most to the observed
cosmic gamma-ray background (here in the 0.05-1 MeV range).  

DIRECTIVITY OF SOLAR FLARE HARD X-RAY AND GAMMA-RAY EMISSIONS

We propose to study the characteristics of solar flare energetic
emissions using the BATSE LAD and spectroscopy detector data.  In
particular. we plan to determine: (1) whether the energetic emission
of solar flares is isotropic or anisotropic: a long standing issue
puzzling solar physicists for years.  If it is anisotropic. we will
further measure the degree of anisotropy and its dependence on time,
energy, and total energy output; (2) the break energy Eb for the flare
spectrum at gamma-ray energies (>100 keV) and the difference in
spectral index below and above Eb, as well as the physical origin of
Eb.  Because it has reached the highest sensitivity ever achieved,
BATSE has observed about four thousand flares up to now, ranging from
small B class to large X class flares, providing a large sample of
diverse data for performing statistical studies of various flare
characteristics. The proposed work will be the first statistical study
of directivity using a sample of more than a thousand flares.  It
should improve our current understanding of solar flare energetic
emissions, and in turn, flare particle acceleration and propagation.

Studies of Gamma-Ray Bursts Time Variability

We propose to use the archive BATSE data to answer two questions: Is
the observed inverse correlation between the burst intensity and time
scale a unique signature of the redshift when combined with other
information, like the observed intensity distribution and spectral
variations?  Is it possible to determine in a model independent way if
the ultimate energy source is active for the whole duration of the
bursts, i.e., up to hundreds of seconds (and possibly longer if
classical bursts are recurrent), or is the observed duration caused by
interaction between the relativistic ejecta and ambient matter, the
original energy release being almost instantaneous.  

Study of Gamma-ray Bursts from Earth

The association of brief gamma-ray bursts from the Earth (reportedly
in the vicinity of thunderstorm systems) add to a significant
menagerie of exotic atmospheric phenomena.  In this correlative study
we propose to carefully analyze the weather associations, review the
data base on the exotica (X-rays in thunderstorms, upward lightning
bolts, radio bursts from thunderstorms), but most importantly the
BATSE viewing-angle/magnetic field orientation since these
relationships should be able to eliminate an entire class of possible
theories.  The goal of this work is to characterize the burst
properties to a degree that plausible hypotheses for their nature
might be possible.  

Source Counts and Spatial Distribution of Ganma-Ray Bursts

In absence of a direct measure of distances to Gamma-ray bursts, for a
knowl- edge on their spatial distribution we must rely on their
logN-logS and angular distributions. This task is complicated because
of large dispersions of their light curves, durations and peak
fluxes. We believe that it is now time to move beyond the current
practice of investigation of V/Vmax and Cp/Clim and that relying
merely on analysis of the peak fluxes is not sufficient and can give
misleading re- sults. For a more complete analysis we need the joint
distributions of peak counts, duration and if possibe fluences. We
propose to do this using some new and in- novative methods which
account for selection biases due' to variation of detection threshold
and finite sampling time, and/or the correlations among the critical
pa- rameters. Analysis of the logN-logS distribution in terms of the
fluence is free of some of these complications. It is also proposed to
use new methods for study of dependence of the logN-logS on the
angular distribution of the bursts.  

A Comptonization Code for CGRO Analysis

We propose to prcide to the connunity a new and inproved version of
the Sunyaev-Titarchuk Comptonization code.  This new code for the
first time takes into account relativistic effects and Klein-Nishina
corrections. The new approach improves considerably over the previous
approach where Conpton scattering was simplified by limiting the range
of photon and electron energies to be where non-relativistic and
diffusion approximations are valid.  The new general code fully
accounts for scattering of photons of arbitrary energies off electrons
of arbitrary energies. This analytic code can be used for practical
purposes such as spectral fitting. As well as making the code freely
available as a callable subroutine, we plan also to use it to make a
nore detailed data analysis of archival CGRO data on black hole
candidates where the typical tenperature and energy range is 20-500
keV and plasma optical depths change between 0.1- 10.  

ELECTRON ACCELERATION IN SOLAR FLARES

We propose to systematically analyze solar flare events detected with
the spec- troscopy detectors of the BATSE instrument on the Compton
Gamma Ray Observatory.  We will invert the observed X-ray spectra to
obtain the instantaneous x-ray producing electron spectrum, and then
use a continuity equation to recover the energy spectrum of
accelerated electrons as a function of time in each solar flare. The
spectra of acceler- ated electrons and their temporal evolution is the
key to understanding the acceleration mechanism in solar flares. Under
our present CGRO G.I. grant we have shown that the BATSE SPEC
observations can provide significant results for such inversion
studies, and extend them to temporal resolutions of ~1 sec, and energy
coverage to well above 100 keV. By systematically studying a large
number of events, we expect to define the general properties of the
electron acceleration and energy release processes in solar flares.

COSMIC RAY STUDIES IN THE LARGE MAGELLANIC CLOUD USING HIGH ENERGY GAMMA RAYS

High energy gamma ray observations provide a direct way to study
cosmic rays, in particular the nucleonic component in external
galaxies.  EGRET has reported the first detection of the Large
Magellanic Cloud (LMC) at energies above 100 MeV. These observations
show clear evidence for diffuse gamma ray emission from the LMC with a
spatial distribution consistent with that expected from the matter
distribution seen at 21-cm and the energetic electron distribution
observed from radio continuum studies. Due to its proximity (~50 kpc
away) and being the only external normal galaxy detected in high
energy gamma rays, the LMC offers an ideal site to carry out studies
on the density distribution and energy spectra of cosmic ray electrons
and protons.  However, the current exposure to the LMC is insufficient
to provide a good determination of the gamma ray spectrum from the
LMC. An additional 8 weeks of EGRET observations on the LMC is
requested.  The gamma ray spectrum derived from combining the proposed
observation with existing data, will significantly enhance existing
information on cosmic rays in an external normal galaxy. 

Observations of Gamma Pay Emission from Supernova Remnants with EGRET

During the EGRET sky survey close to 40 as yet unidentified sources
were detected at low galactic latitudes.  We have evidence that some
of these are associated with galactic supernova remnants and propose
to further investigate this correlation. The hypothesis that nucleonic
cosmic rays are produced in SNRs has led to estimates on their gamma
ray brightness and spectrum. The brightness depends on the density and
structure of the surrounding medium and possibly on the presence of a
neutron star. The spectrum released by freshly accelerated particles
in a SNR could be considerably harder than `the general diffuse
emission.  New EGRET data with increased statistics will help to
clarify the important questions of the spectra at higher energies, the
possible extend of some sources, whether there is a subset of SNRs
that emit gamma rays and possible source variability, which would cast
doubt on a SNR interpretation. We request new observations in two
regions of the galactic disk and access to data of a list of sources
that might become available during cycle 4. Finally we propose to
monitor SN1987A with EGRET. In June 1993 EGRET detected a source
coincident with SN1987A (about 4 sigma significance) which was not
visible previously.  SN1987A has recently (1992) been found to
brighten in the soft X-ray and radio band and a gamma-ray observation
of this expanding SNR is urgently required.  

Gamma-ray Production in Infrared Luminous Galaxies

One of the major discoveries of the IRAS satellite was the detection
of ultraluminous infrared galaxies. A complete catalog of 324 bright
galaxies, 60 micron flux densities greater than 5 Jy, has been
selected from the IRAS catalogs by Soifer et al., 1988. The infrared
ultraluminous galaxies were found to be an important component of
extragalactic objects, being the most numerous objects in the local
universe at luminosities above 10^11 Lo. However, very little is known
about the nature of these objects. Multi-welength observations of the
nearby infrared luminous galaxies must be undertaken.  Deep gamma ray
observations using the EGRET and OSSE instruments aboard the Compton
GRO are needed to increase our understanding of the infrared luminous
galaxies and to investigate the possible relation of these objects to
active galactic nuclei.  

Search for Galactic Gamma-Ray Line Emission Using BATSE

We propose to continue our Phase 3 search for gamma-ray line emission
in the Galaxy, particularly transient 511 keV positron annihilation
radiation both from known black hole candidates and new sources. We
will also try to measure (and eventually map, using Earth occultation)
the diffuse Galactic 511 keV and 1809 keV lines.  Other objectives
include detection of the 1157 keV 44Ti line from Cas A observed by
COMPTEL, and 56Co lines which would indicate a recent, hidden Galactic
supernova. We have developed the only data analysis software taking
full advantage of the BATSE continuous high-resolution spectral data
in the HER and SHER formats.  We present significant upper limits on
transient - annihilation emission from x-ray Nova Persei (GRO
J0422+32) from Phase 3.  

Cosmological Gamma Ray Burst Models:  Signatures and Constraints

The large quantity of data accumulating from GRO on Gamma-ray Bursts
depends crucially for its interpretation on comparison with
theoretical models. These must identify and incorporate the relevant
physics, and provide specific predictions on observational quantities.
Building on our previous encouraging results, we will develop models
of cosmological GRB sources with unsteady energy inputs, incorporating
various dissipation mechanisms, and will examine the consequences of
magnetic fields in the flow. Alternative galactic models will also be
considered, and quantitatively compared against cosmological
ones. Various observational signatures will be calculated and
contrasted between models and the data.  Among these are the relation
between total burst energy and duration, temporal structure as a
function of input energy source, hardness versus duration and fluence,
characteristic multi-waveband spectra1 and spectral time evolution for
different burst types.

OSSE SEARCH FOR HARD X-RAY EMISSION FROM BURSTERS

Stimulated by the recent SIGMA detections of several neutron star
systems. here we propose OSSE observations of two X-ray bursters:
XB1916-053 and 4U0614+09l. Taking advantage of the unprecedented
sensitivity of OSSE, we will be able 1) to obtain high quality hard
x-ray spectra of these two neutron star systems, 2) to study their
daily spectral and temporal variability. This will enable us to make
reliable comparisons of their observed properties with the known
characteristics of black hole candidates.  We also plan to propose for
simultaneous or at least contemporaneous observations below 10 keV
with ASCA, and have a complementary proposal to monitor these tw0
sources in the 20-100 keV band, using archival (Phase 1-3) and Cycle 4
BATSE data.  

Measurement of MeV Continuum Sources with BATSE

We propose to expand the BATSE data analysis package being developed
at University of Maryland (see proposal ÒSearch for Galactic GammaRay
Line Emission Using BATSEÓ) to search for high-energy continuum
emission. Using spectroscopy detector SHER data at low gain, we can
search for variable emission up to 10 MeV or higher from Cyg X-1 and
the Galactic Center. This will complement work already being done with
the BATSE LADs on Cyg X-1 (e.g.  Ling et al.  1993) up to 1.8 MeV. We
will test our algorithm by comparing its LAD results to the results of
the standard Mission Operations System (`MOPSÓ) occultation software
for a blank patch of sky, the Crab, and Cyg x-1.  

Solar Flare Hard X-Ray Spectroscopy

As a continuation of our Phase 2 and 3 CGRO/GI efforts, we propose to
conduct a three part effort to support the analysis of BATSE solar
flare data with particular emphasis on hard X-ray spectroscopy. The
three efforts include: (1) The expansion and maintenance of a software
and database environment capable of supporting all users of BATSE
solar data as well as providing expertise and effort to the BATSE
solar GI community. (2) The continued participation with the PI team
and other Guest Investigators in the detailed analysis of the BATSE
detectors' response at low energies and high counting rates. (3) The
first systematic study of the Super Hot Component of solar flares
using late phase hard X-ray spectra from 10-40 keV.

Analysis of Simultaneous Solar Flare X-ray and Microwave Spectra in
Terms of the Direct Electric Field Heating and Acceleration of
Electrons

We propose to analyze and interpret simultaneous, high-resolution
solar flare x-ray spectra from BATSE/SHERB and microwave spectra from
the Owens Valley Radio Observatory (OVRO) in terms of the direct
electric current heating and acceleration of electrons. This will be
the first detailed analysis of simultaneous hard x-ray and microwave
spectra containing significant spectral structure. This study will

- test the applicability of the model and, therefore, the direct electric field
   particle acceleration mechanism to a variety of flares.

- provide a better understanding of the relationship between the energetic
  electrons responsible for the x-ray and microwave emissions.

- provide quantitative information about the physical properties of the
  acceleration region and their evolution, as required by the model.

Preparing the EGRET Archive Legacy:

The EGRET instrument on GRO has provided the first survey of the
entire sky in the high-energy gamma-ray regime. While the entire sky
has been seen by the EGRET instrument to some level of exposure, there
are several regions where the exposure is relatively low. To maximize
the value of EGRET observations as an archival resource and to get the
greatest chance of discovering new phenomena with EGRET we propose
several pointings which will fill the deepest holes in the EGRET
data. We propose to provide supplements to the standard pipeline
products to enhance the usefulness of the EGRET data to archival
investigators.  

Search for soft gamma-ray events (25-55 keV) in the BATSE data base

We propose to continue our search of the BATSE channel-I data base for
soft (25-55 keV) events which do not lead to a burst trigger (in
channels 2+3). In our work so far we have optimized the search
strategy.  We have applied the software to scan more than two years of
BATSE data so far, and have fully analyzed the results for half a year
of data. We have detected an excess of very weak soft events from the
sky region near SGR 1900+14 when this source was known to be active.
We are currently investigating the systematic and statistical
accuracies of the locations based on channel-I data.  

Distribution of GRB Coordinates in Real Time for Multi-band Follow-up
Observations


We propose (1) to continue to operate the BATSE Coordinates
Distribution Network (BACODINE), (2) to improve the Gamma Ray Burst
(GRB) location accuracy of BACODINE, and (3) increase the number of
methods/media by which the locations are distributed.  BACODINE is a
system of computers and programs that extracts GRB locations from the
BATSE telemetry data in real time and distributes those positions to
instruments to make multi-band follow-up observations of GRBs in real
time -- a few seconds. Historically, optical observations of GRB error
boxes have been delayed by weeks to years and the source objects for
GRBs are still unknown. Our approach is to allow the making of
multi-band observations of the GRBs while they are still in progress
(5 to 15 sec typical delay from the beginning of the burst to the
actual observations).  This should provide a new tool for GRB
research.  At the very least, coordinated observations will set new,
more stringent upper limits to GRB models, and at the most, will make
a positive identification of a GRB source object.  

Aperiodic Flux Variability in A0535+262

During February and March of 1994 the x-ray binary pulsar A0535+262
underwent a major out-burst, which was observed by BATSE. Power
spectra reveal a very significant noise concentration in a bump with a
relative width of approximately 50% varied between 35 and 70 mHz, and
was highly correlated with preliminary estimates of the neutron star
angular acceleration. We propose a systematic study of the flux
variablity of A0535+262 during this outburst. Comparison of power
spectral parameters with mass accretion rate indicators such as flux,
angular acceleration, energy spectral state and pulse shape during the
course of this outburst should provide a powerful probe of the
accretion process in x-ray pulsars.  

High Resolution OSSE Scanning Observations of the Galactic Center 511
keV Source

Satellite and balloon instruments have confirmed the discovery by
M. Leventhal et at. of a narrow line source of 511 keV gamma-rays in
the galactic center (GC) region. The next step is to identify the
source or sources of annihilating positrons. OSSE should be able to
provide a more precise determination of the galactic distribution, but
there have been only two scans of the GC in OSSE's highest spatial
resolution mode (collimator perpendicular to the plane). These
indicate that the center of the line emission is offset from the GC in
longitude (-l.I6+/-0.33 deg; ~4 sigma). We propose to repeat this
measurement with an improved technique and test the spatial
coincidence with 1E1740.7-2942. This observation will also test a
predicted increase in 511 keV flux due to beam dynamics in
1E1740.7-2942.  

Testing Solar Flare Models with BATSE

We propose to use high-sensitivity BATSE hard X-ray observations to
test the thick- target and electric field acceleration models of solar
flares.  We will compare the predictions made by these models with
hard X-ray spectral observations obtained with BATSE and simultancous
soft X-ray Ca XIX emission observed with the Yohkoh Bragg Crystal
Spectrometer (BCS).  The increased sensitivities of the BATSE and BCS
(relative to previous detectors) permits a renewed study of the
relationship between heating and dynamical motions during the crucial
rise phase of flares.  With these observations, we will:

   1. investigate the ability of the thickÑtarget model to explain the temporal
      evolution of hard X-ray emission relative to the soft XÑray blueshift 
      during the earliest stages of the impulsive phase.
   2. search for evidence of electricÑfield acceleration as implied by temporal
      correlations between hard X-ray spectral breaks and the Ca XIX blueshift.

The proposed study will utilize hard XÑray lightcurve and spectral
measurements in the 10Ñ100 keV energy range obtained with the BATSE
Large Area Detectors (LAD).  The DISCLA and C0NT data will be the
primary data products used in this analysis.  

Study of Variability of Unpulsed Gamma-Ray Emission From the Crab Nebula

We propose correlated EGRET and COMPTEL Phase 4 observations of the
Crab nebula to study the possible variability of the unpulsed
gamma-ray emission discovered in our Phase 2 observations.  One 3-week
pointing is requested to look for changes in flux between Phases 1 and
4, thus confirming that the Crab nebula is variable at gamma-ray
energies.  We plan to analyze the data and fit the resulting spectra
with improved synchrotron-self Compton model calculations that predict
variability only below ~1 GeV.  We seek to confirm the lack of
variablity seen above 1 GeV between Phases 1 and 2, as predicted by
this model to be a steady inverse Compton component.  If possible, we
will arrange for simultaneous observations at optical and radio
wavelengths to detect possible wisp motion and changes in scattering
properties in the nebula.  

Modelling Radiation Production and Attenuation in Gamma-Ray Bursts

This proposal requests funding for the theoretical modelling of the
production and attenuation of gamma-ray burst continuum spectra. We
plan to calculate the optical depth of magnetic two photon pair
production in neutron star field geometries, thereby ascertaining how
the field and its curvature influence the attenuation of burst spectra
and the associated observational spectral constraints on radiation
beaming in GRB emission regions. We also propose to extend a
comprehensive Monte Carlo code that is currently under development,
which describes radiation production and electron cooling in strong
magnetic fields. Substantial improvements to this hybrid synchrotron
pair cascadeIresonant Compton scattering code will be the inclusion of
Coulomb scattering and pair annihilation, to accurately model electron
thermalization, and also neutron star field geometry to study its
effects on source spectra. A major emphasis will be on fitting BATSE
and EGRET source spectra, to obtain valuable clues to whether bursts,
a few or many, can still be in a galactic halo rather than
cosmological in origin.

Deep Searches for Counterparts of Gamma Ray Bursts

The nature of Gamma Ray Bursts is on of the biggest mysteries in
astrophysics. The most likely solution would come from the detection
of even one confident counterpart at lower energies.  Previously, deep
searches have not revealed any counterparts. Recently, significant
improvements in search techniques can be made due to advances in
detector technology (e.g., lR arrays), the rapid availability of burst
positions (as fast as 6 hours after the burst), and the many
sub-square-arc-minute positions from the Interplanetary Network (due
to the large area of BATSE and the great distances to spacecraft such
as Ulysses). We propose to use these advances to pursue deep and rapid
searches of many positions in the optical, infrared, and radio. If we
do not find any counterparts, then the lack of any host galaxy will
strongly refute broad classes of extragalactic models. If we do find a
counterpart, then detailed observations will reveal the nature of the
components in the burst system.  

Can Bright LMXBs Have Hard X-ray Tails?

We propose OSSE observations of the luminous low-mass X-ray binaries
Cyg X-2 and Sco X-1. In both cases, the observational evidence exists
for hard, possibly time variable, tails above the thermal
continuum. OSSE sensitivity is adequate to detect or reject these
tails conclusively and address the various spectrum models that exist
for LMXBs. We also propose matching observations with BATSE, which
will expand the spectral and time coverage.  

Multiwavelength Observations of X-Per = 4U 0352+30

We propose to observe the Be binary X-ray pulsar X-Per with OSSE and
BATSE.  This object is unique in its long pulsar period and long
binary period.  As such, it samples an accretion environment different
from most Be binaries. In addition, the Be star appears to undergo
phase changes, occasionally losing its circumstellar disc. This may
have a significant effect on the amount of material accreting onto the
neutron star. OSSE and BATSE are in a position to conclusively
determine the shape of the spectrum from X-Per at hard X-ray energies
and to perform other spectrum and timing measurements vith
unprecedented sensitivity.

Continued OSSE Sky Survey Observauons

We propose to continue OSSE sky survey observations in Cycle 4 of the
COMPTON Observatory Mission.  During Phase 3, OSSE sky survey
observations were initiated with observations of the Virgo region in
coordination with EGRET and COMPTEL.  We have demonstrated the
capability to use OSSE for survey work in a mapping mode.  Data have
also been obtained which will provide results on broad band spectra
and temporal variability of sources in the Virgo region.  In Cycle 4
we propose an OSSE survey in the region of the North Ecliptic
Pole. This is a region rich in AGN and which has been extensively
observed by several x-ray missions. This program continues work toward
a first sensitive low-energy gamma-ray sky survey which could be
accomplished on an extended COMPTON mission.  

OSSE Observations of Blazars

We propose OSSE observations of selected active galactic nuclei (AGN)
which have been previously detected at energies above 30 MeV by EGRET.
These observations, coordinated with the proposed COMPTEL and EGRET
blazar studies, shall provide complementary spectral and temporal
measurements in the 0.05 - 10 MeV energy range for five AGN, all of
which have been seen by EGRET, OSSE, and/or C0MPTEL. The AGNs proposed
for observation include, QSO 0202+149, PKS 0506-612, PKS 0528+134, QSO
2251+158 and PKS 2155-304.  An OSSE target of opportunity is also
proposed in response to a EGRET- detected blazar ÒflareÓ.  The
observations will be used to constrain models of the gamma-ray
emission from blazars.  

Theoretical Studies of Gamma-Ray Emission from Pulsars

We propose to investigate the high-energy emission from radio pulsars
(including millisecond pulsars) and Geminga, and to use these results
to explore statistical properties and evolutionary behavior, and to
gain information about the pulsar acceleration mechanism. We plan to
examine in detail a resonant Compton scattering model to produce the
gamma rays, and compare its predictions for the observed number, age
distribution, pulse profiles, spectra, and gamma-ray efficiencies of
gamma-ray pulsars with other polar cap and outer gap models. Topics to
be treated are: inclusion of nonresonant Compton scattering, curvature
radiation, and an improved treatment of synchrotron processes in the
radiation model; polar-cap heating through a treatment of the dynamics
of the relativistic electron and pairs; X-ray and gamma-ray wave
propagation in pulsar magnetospheres and implications on pulsar
geometry.

"SHOCKED JET" SELF-COMPTON X-RAY MODELS FOR BLAZARS

It is generally accepted that emission from blazars originates in a
relativistic jet. The radio through UV spectrum is explained by
synchrotron emission but the x-rays are probably synchrotron self
Compton emission.  Variability arises from shocks in the jet. The
major prediction of Òshocked jetÓ models is that x-ray should precede
millimetre variations, and be well correlated with them. Correlated
x-ray/mm short time scale variations have already been observed in a
simultaneous X-ray and mm monitoring campaign of 3C273. It is
important then to investigate if the long timescale X-ray variations
are also correlated with the large amplitude flares observed in the mm
light curve of this source. For this reason, it is necessary to
determine the long time scale, high energy light curve of 3C273. BATSE
can help us in this task, and so we ask here simply for low-level
access to the archival data of 3C273.  

Coordinated Observations of NGC 4151 and MCG -6-30-15: Defining the
Gamma-Ray Signature of Seyfert 1's

We propose a campaign of simultaneous GRO/OSSE, ASCA and IUE
observations of two gamma-ray bright Seyfert 1's, NGC 4151 and
MCG-6-30-l5.  For NGC 4151 our goal is to add to previous observations
to produce the highest precision UV to gamma-ray spectrum ever
accumulated for an AGN. We will use this to test and refine the new
Seyfert models (e.g., thermal/nonthermal hybrid and the
relativistically corrected Comptonized) and to perform multiwavelength
variability studies. It will also add statistics for an eventual 511
keV line search with enough sensitivity for a definitive test of
nonthermal models. For hiCG-6- 30-IS our goal is to address the
question: Is the ~80 keV spectral cutoff in NGC 4151 also present in
more-typical Seyfert 1's? Proposals to ASCA and 1UE have or will be
submitted.

Joint BATSE/COMPTEL study of spectral shape and evolution in gamma-ray bursts
 
The confirmation of homogeneous, isotropic distribution of GRBs by
BATSE, coupled with an apparent time dilation effect in the time
profiles of weak bursts, lend support. to the cosmological hypothesis
for the origin of GRBs.  The characterization of GRB spectra may also
shed light on this issue.  In particular, is the predicted correlation
between burst hardness and intensity, for a cosmological distribution,
actually observed?  We wish to continue the spectral analysis of GRBs
observed by COMPTEL and BATSE on board GRO (from 10 keV to 10 MeV)
which is currently in progress with Phase 3 data, in an attempt to
address the question of the origin of the GRBs. The complementary
energy ranges of the two instruments enables both the low energy
turnovers and the high energy tails in GRB spectra to be well
characterized.  The model fitting will be performed simultaneously on
both sets of data using the BATSE Wingspan software.  Furthermore, the
variability of spectral shape during bursts will be studied using the
high time resolution BATSE LAD data.  

Prompt Radio Counterparts of Gamma Ray Bursts

We propose to use rapid gamma ray burst position estimates from BATSE
to make a real-time search for associated radio emission, using a
dedicated telescope array in Fallbrook, California.  Detection of
prompt radio emission from any bursts would be a significant
breakthrough towards understanding the burst mechanism.  Measurement
of the dispersion delay between radio and gamma ray energies would
yield a distance estimate to the burst, and hence set the burst energy
scale.  This experiment is made possible by the unique sensitivity and
fast-response capability of BATSE, and will be done in close
collaboration with BATSE team members.  

Modeling of Novae: The Nucleosynthesis of Gamma-Ray Emitters
Observable by 0SSE and COMPTEL

We propose to hydrodynamically model the time-dependent structure of
classical novae with emphasis on the nucleosynthesis products
observable by Compton Gamma-ray Observatory. Previous calculations of
the production of prompt 0.511 MeV annihilation photons due to
short-lived nuclei such as 13N and 18F, and the production of the
gamma-ray emitting nuclei 7Be, 22Na, and 26Al, are not accurate enough
to support the detailed interpretation of the gamma-ray lines CGRO may
detect. Our nova models will be fully self-consistent and include a
nuclear reaction network large enough to allow the simultaneous
modeling of the dynamics and the nucleosynthesis. This network will be
fully coupled to a nuclear species diffusion algorithm and the
hydrodynamical evolution of the nova. We will emphasize how the mass,
radius, and composition of the white dwarf will affect the
nucleosynthesis yields of the gamma-ray emitters.  

BATSE Long-Term MIonitoring of Active Galactic Nuclei

We will use the BATSE Earth occultation technique to produce the first
hard X-ray light curves to span time scales of days to years for 3C
273 and other bright AGN, without any pointed CGRO time. This will
allow us to probe the long time scales predicted by theory, and
determine the characteristic variability time scales.  By focusing on
sources that have been monitored intensively at lower energies, we can
use continuum cross-correlation functions to relate the hard X-rays to
other bands, allowing a key test of reprocessing models.  We will
determine how the spectral slope and cutoff vary as a function of
brightness, to test Comptonization and pair production
models. Finally,. we will look for an anticorrelation between
luminosity and variability. which would yield evidence for isotropic
emission.  

SEARCH FOR REPEATING SOURCES OF CLASSICAL GAMMA-RAY BURSTS

We propose to complete our search and analysis of the BATSE gamma-ray
burst data for possible repeating sources of the classical bursts. We
found several pairs of candi- date repeating bursts in the First BATSE
Ca.talog sample that were so closely clustered in both position and
time, that the Poisson probability of their random occurrence was only
~2x10^-5 But because onboard tape recorder failures seriously reduced
the number of ac- curately positioned bursts in the Second Catalog, it
did not allow us to either confirm, or refute, the predicted
repetition.  Thus, we need to analysis the forthcoming Third Catalog
positions, which will be more precise and complete, in order to
determine whether BATSE has observed fast (< few day) repeating burst
sources. We also propose to complete our Monte Carlo simulations of
burst repetition to set limits on the fraction of the BATSE bursts
that could come from sources that repeat in less than a few
years. This work will complete the doctoral dissertation research of
V. C. Wang.  

DETERMINATION OF THE SOLAR-FLARE PHOTOSPHERlC SCALE HEIGHT FROM
COMPTEL GAMMA-RAY MEASUREMENTS

Using a new diagnostic technique, we propose to directly determine the
effective photospheric scale height in solar flares from the neutron
capture gamma-ray line measurements by the COMPTEL experiments, and
critically test current photospheric models whose scale heights differ
by as much as a factor of 3.  We show that from the measurements of
the 2.223 MeV neutron capture line time dependence, we can determine
the mean density in the capture region, and from the relative flux in
Compton scattered line photons at energies below the line, we can
determine the mean column depth to that density. The column depth
divided by the density gives us the effective scale height. Thus, we
propose to analyze the COMPTEL measurements of the June and October
1991 flares, using Monte Carlo simulations of the time dependence of
the 2.223 MeV line emission and Compton scattered excess below the
line for differing photospheric models, to determine the photospheric
scale height and test the current models.  

Study of Pre- and Post- Emission Spikes Near BATSE Triggers

Many GRBs are known to have uncatalogued pre or post- cursory
emission.  We propose to systematically analyze 1000 seconds of pro
and post- trigger DISCLA data to identiiy outlying emission related to
triggered GRB events. These outliers are important for GRB duration
and time dilation comparisons. We wIll investigate whether any
outliers are related to post-cursory emission seen in the X-ray by
Ginga and in the hard gamma-ray by EGRET. These outliers wl1l be
compared to the triggered peaks for gravitational lensing on an
intermediate time scale never before searched.  A list of these
outliers will be published in collaboration with the BATSE team.

Investigation of Comparative Phenomenological Aspects of Atmospheric
Gamma-Ray Bursts

The BATSE team has recently announced the discovery of a new class of
gamma-ray bursts - those originating from the atmosphere of the earth
(Fishman et al. 1994). In two years, 12 such atmospheric GRBs have
been detected. The precise progenitor mechanism is yet unknown
although they appear to be correlated with regions of thunderstorm
activity. We propose to more precisely quantify phenomenological
aspects of atmospheric GRBs in order to facilitate a resolution of
their origin. We will compare these results to attributes of several
types of upper atmospheric discharges. We will also compare these
atmospheric GRBs to cosmic GRBs in an attempt to better understand
common attributes and systematic errors.  

MULTIWAVELENGTH BLAZAR STUDIES

EGRET observations are proposed on a number of blazars for studies of
3 specific aspects of their gamma ray emission: (I) Continuation of
the observations begun in Phase 3 on gamma-ray variations as a key
element in multiwavelength variability studies.  Such multiwavelength
studies are thought to be crucial in choosing between the various
models vhich have been proposed to explain the emissions.  Included in
this topic is a request for possible extension of observations (Target
of Opportunity) in which etremely bright gamma-ray emissions are
detected in the EGRET quicklook data: (2) Observations of nearby (z <
0. II) BL Lac objects, both to identify likely targets for TeV
observations and to obtain additional information on the 4 such
objects vhich have been previously detected by EGRET: (3) New
observations of the closer (z < 0.6) of the blazars previously
detected by EGRET, as well as several similar objects which are so far
undetected by EGRET.  The goal of these observations is to study the
variability range and quiescent fluxes of the objects, as well as
possible evolutionary effects.  

Gamma Rays fron Classical Novae

Classical novae provide environments in which hydrogen-burning
reactions proceed on CNO and heavier nuclei at high temperatures. For
such conditions, there exist several possible mechanisms by which
astrophysically significant fluxes of gamma rays can be produced, that
may be detectible with the Compton Observatory. These include: (1) the
positron decays of the short lived unstable isotopes of CNO nuclei
(13N, 14O, 15O, 17F, and 18F) which have been carried to the surface
region by convection can drive a phase of gamma ray emission during
the earliest stages of the outbursts; (2) the decay of 22Na can
produce a detectible flux of 1.275 MeV gamma rays on a timescale of
order two years after the outburst, particularly in novae enriched in
the elements neon-to-aluminum; and (3) the production of 26Al in these
same enriched nova envelopes can contribute to the flux level of 1.809
MeV gamma rays in the Galaxy reported by Mahoney et al. (1984). We
propose a continued effort to provide improved theoretical estimates
of gamma ray fluxes from these various sources.  

SEARCH FOR NUCLEAR LINES FROM MASSIVE OB ASSOCIATIONS M 17 and RCW 131
WITH COMPTEL

Intense gamma-ray line emission at 4.44 and 6.13 MeV from the nuclear
de-excitation of 12C(4.44) and 160(6.13) has recently been discovered
(Bloemen et al. 1994) by the COMPTEL experiment from the Orion
complex, a nearby (~450 pc) molecular cloud with a resident
association of massive OB stars. This emission is apparently produced
by low energy (<30 MeV/nucleon) cosmic rays, which are accelerated in
the complex by supernova shocks and undergo nuclear interactions with
the dense gas in the cloud. To test this hypothesis, we have
identified several similar candidate OB associations from which we
would also expect comparable, or greater, fluxes in these two nuclear
gamma-ray lines. There are archival COMPTEL observations that include
the two most promising of these sources, M 17 and RCW 131 complex,
with at least ten viewing periods totaling twenty weeks on each
source.  We propose to analyze the spectra from these two source
positions to look for the expected line emission in collaboration with
the COMPTEL team.  

Gamma-Ray Burst Recurrence

This is a collaborative proposal with the BATSE Team in which archival
and proprietary data will be analyzed to address the question of burst
repetition.  We propose to use angular correlation analysis as well as
nearest neighbor statistic to search for clustering on small angular
scales, either due to enhanced burst actiYity from large spatial
structures or intrinsic repetition from one or more sources.  We also
propose to extend multipole analysis beyond dipole and quadrupole.
"HotspotsÓ on the sky map will be analyzed.  Their shape might
distinguish between clustering and repetition.  We also propose to
study source evolution which affects theoretical recurrence rate
estimates.  

OSSE Observations of the Diffuse Galactic Lo-Energy Gamma-Ray
Continuum

The spectrum and spatial distribution of the diffuse Galactic
low-energy gamma-ray continuum contalns important information on the
production and transport of cosmic-ray electrons in the Galaxy.  The
OSSE energy band is particularly important, for if the dlffuse
Galactic gamma-ray continuum measured with EGRET and COMPTEL extends
down to OSSE energies and is interpreted as electron bremsstrahlung,
then the electrons responsible require a power of ~10^41 ergs/s.
Furthermore, most of this power gets deposited into the interstellar
medium and could provide the heating and ionisation required to
maintain the warm (10^4 K) partially ionised component of the
interstellar medium. We propose OSSE observations of the Galactic
plane in the directions I = 310, I = 50¡ and I = 140¡. These
observations will supplement previous OSSE observations and be used in
conjunction with measurements made with other instruments on CGRO to
constrain models for the production and distribution of the dlffuse
Galactic low-energy gamma-ray continuum.

Gamma-Ray Observations of New Pulsars Associated with Unidentified
EGRET Sources

The EGRET and COMPTEL instruments on the Compton Gamma Observatory
(CGRO) can be used in combination with radio observations to search
for new radio pulsars associated with unidentified gamma-ray
sources. We have searched the regions near seven sources released in
1992 that were located with in the Arecibo observatory declination
range. The search resulted in the discovery of the new binary
millisecond pulsar J0751+18, with the fastest known orbital period of
a binary system in the galactic field.  Continued searches of
unexamined error boxes and follow up observations on the possibly time
variable gamma-ray source associated with PSR J0751+18 is critically
important to the study of pulsar emission mechanisms and evolutionary
scenarios.  

Accurate, Simultaneous Gamma Ray Burst Position Determination Using
the Burst And Transient Spectroscopy Experiment (BATSE) and the
Explosive Transient Camera (ETC).

The ETC is a fully automated optical transient detection facility
dedicated to the search for optical flashes spatially and temporally
coincident with gamma-ray bursts (GRBs).  Operational since 1991, the
ETC currently observes -3 BATSE-localized GRB/yr coincident with
BATSE. Any coincident flashes are localized to ~10Ó accuracy, ~10^5
times finer than BATSE alone. To date, 4 ETC/BATSE coincidences have
been detected -- none of which have associated ETC optical
flashes. With improvements currently underway, the number of ETC/BATSE
coincidences will rise to ~1 per month in FY95. A close collaboration
with the BATSE and BACODINE teams, proposed here, will establish and
rapidly disseminate small (~10Ó) error boxes from positive ETC
detections for multiwavelength astronomical studies.  

TIMING THE GEMINGA PULSAR UITE BIGE-ENERGY GAMMA RAYS

One of the major achievements of high-energy astrophysics in this
decade was the determination that Geminga is a 237 ms,
rotation-powered pulsar, radiating mainly in high-energy gamma rays.
The unique contribution of Geminga to the study of pulsar emission
mechanisms and spin-down demands ongoing observations by EGRET to
refine the pulse ephemeris and improve the statistics of its pulse
profile and phase-resolved spectra. We propose a 2 week duration
observation in cycle 4 to continue this effort. With the help of 2
more years of EGRET data, it will be feasible to link the phases and
count cycles between EGRET, COS-B, and SAS-2, representing a 24 year
baseline.  Possibly the braking index will be measured, and/or the
timing noise more precisely characterized.  Another important use of
these data will be as an ephemeris to support future studies at other
wavelengths.  

A PROGRAM TO STUDY TEE DISTRIBUTION OF GAMMA-RAY BLAZAR SPECTRA AND
MULTIUAVELENGTB VARIABILITY

One of the most exciting Compton Observatory results is the EGRET
detection of the Blazar class of AGN. We propose a program intended to
compliment the EGRET team Blazar monitoring programs, and thus fully
utilize the critical opportunity provided by EGRET to study
high-energy processes in Blazar jets.  We propose a target list of 359
likely gamma-ray Blazars.  This list consists of of all non-extended
radio sources in the sky with F(5Gz) > 800 mJy, and spectral index >=
0.2. We also propose an EGRET triggered multiwavelength observation
program which will dramatically increase the probability of obtaining
a crucial result with EGRET before the depletion of its spark chamber
gas: a determination of how the time variation of the gamma-ray flux
correlates with time variation of longer wavelength flux during a
flare.  

A Search for Optical Counterparts of Gamma Ray Burst Events

A search for the optical counterparts of gamma-ray burst events has
recently begun, using a wide-field-of-view camera built at Lawrence
Livermore National Laboratory. The camera can rapidly slew to any part
of the sky under computer control and has an angular acceptance of
about 0.6 steradians. By using GRB coordinates supplied by the
BACODlNE network, the camera can slew to the designated target within
12 seconds of the BATSE initial detection. With a limiting magnitude
of approximatly 8, this device is competitive with other current
attempts to obtain simultanious gamma ray and optical detections. The
system has been in routine observation mode since January 1994. A
second generation detector system is under construction with an
anticipated factor of 100 increase in sensitivity.  

Target of Opportity Observations of Nearby Novae in Outburst.

A nova is the largest hydrogen ÒbombÓ in the universe and theoretical
calculations predict that they eject astrophysically interesting
amounts of the radioactive isotopes 7Be (T1/2=53.28 days), 22Na (T1/2=
2.605 yrs), and 26Al (T1/2 = 7.2 x10^5yrs). If a new nova is bright,
with Vmax less than about 2, then it is likely to be sufficiently
close to the sun for the gamma-rays emitted by the decays of 7Be and
22Na to be detected by the OSSE instrument on the Compton
GRO. Therefore, we propose to observe any bright nova, which appears
during this observing cycle, as a Target-of-Opportunity with Compton
GRO. In this proposal we present the theoretical and observational
results that lead us to the conclusion that such a nova wi1l be
detected in a two week observing session.  

Background Modeling for the 0riented Scintillation Spectrometer
Galactic Science Survey

We propose to improve OSSE background modeling as part of the OSSE
Diffuse Galactic mapping project.  A survey of the galactic plane will
provide detailed measurements of the spectrum and distribution of
galactic positron annihilation radiation, the amount and distribution
of freshly synthesized radioactive nuclei such as 26Al, 7Be, 22Na, Ti,
and 60Fe, the characteristics of the low-energy gamma ray continuum,
and will also permit searches for new weak or transient
sources. Errors of background subtraction are critical for mapping
because of the weakness of the emissions under study.  The work will
also support the OSSE Sky Survey and lead to improved point source
analysis. The investigators bring to the task experience with both
OSSE and with background on virtually every major US space low-energy
gamma-ray experiment in the past 20 years.  

Deep COMPTEL/OSSE Spectroscopy of Energetic Particle Interactions in
Orion/Monoceros

COMPTEL has detected gamma-ray emission from the Orion complex in the
3-7 MeV range, which can be identified with the deexcitation lines of
carbon and oxygen nuclei at 4.44 and 6.13 MeV. These lines can only be
produced by accelerated particle interactions, in contrast with all
the other observed astrophysical (non solar) nuclear deexcitation
lines which are formed following the decay of long lived
radionuclei. The COMPTEL observations of Orion thus open a new chapter
in astrophysical gamma-ray spectroscopy.  Since the COMPTEL exposure
of the Orion complex during Phases 1-3 was limited (OSSE has not
observed Orion at all), we propose a deep combined COMPTEL/OSSE
observation with the following objectives: a) confirm the initial
finding, b) distinguish predominantly narrow line emission from broad
line emission, which has major astrophysical implications, c) search
for accompanying lines in the 1-3 MeV range, which set important
constraints on composition and particle spectra, d) observe the 511
keV annihilation line due to positron production by accelerated
particle interactions, and e) observe the continuum
electron-bremsstrahlung emission at MeV energies, which sets a unique
constraint on the low-energy electron spectrum. In order to optimize
the COMPTEL viewing and to take full advantage of all the existing
anti-center observations of Crab and Geminga (located at an angular
distance of ~25 deg from Orion), we propose a mosaic of three
observations. This also provides very good exposure of the Mononoceros
complex, which is a most promising target region located ~20 deg from
the Orion complex.  

GAMMA RAY OBSERVATIONS OF THE ORION CLOUD REGION WITH EGRET

The Orion cloud complex , owing to its proximity, large mass and solid
angle, is ideally suited for the analysis of its gamma ray and radio
emission to determine the uniformity of the cosmic ray intensity on
the scale of a molecular cloud, identify regions of possible enhanced
cosmic ray density, and determine the molecular mass.  We propose to
conduct a detailed investigation and analysis of the Orion cloud
region using EGRET data.  The existing exposure, however, is poor and
uneven.  With an additional well centered observation we should be
able to better distinguish cosmic ray excesses from background compact
sources and variations in molecular column density.  

ANALYSIS AND MODELING OF THE HERCULES X-1 CYCLOTRON LINE

The cyclotron line at 35 keV in the spectrum of the accretion-powered
pulsar Her X-1 affords an opportunity to calibrate the BATSE
Spectroscopy Detectors (SDs), and to study the shape and strength of
the line as a function of pulse phase.  This we propose to do. First,
we will obtain several additional SD observations of Her X-1 during
the high state of its 35-day cycle.  Second, we will carry out a joint
fit to these observations and to four earlier observations of Her X-1.
Extensive simulations show that such a joint fit should detect the
cyclotron line with high significane (Q-value ~l0^20) and thereby
calibrate the sensitivity of the SD to lines like those seen by Ginga
in a few gamma-ray bursts. Third, we will confront extensive Feautrier
radiation transfer calculations of the Her X-1 line spectrum with
BATSE SD data, once the line is established.  

COMPTEL AND OSSE OBSERVATIONS OF NEARBY SUPERNOVAE: 1994-1999

We propose to use the OSSE and COMPTEL instruments to further
understand the natures and details of supernovae of Types Ia, II, IIb,
and Ib.  Each will require a relatively rare nearby event, but the
probability of each, small in any one year, is at least several
percent over the remainder of the Compton Observatory lifetime. For
this reason and because the required observations of a single
supernova will likely extend beyond a single proposal cycle, we submit
this multi-year proposal. We seek the opportunity to observe the first
good candidate of each class. Of course, supernovae are discovered at
the rate of a few dosen per year, but the most important
characteristic for Compton Observatory detectability is distance.  We
propose to observe any verified Type Ia closer than 10 Mpc, any Type
Ib/IIb closer than 4 Mpc, and any standard Type II in the local group
of galaxies. The COMPTEL and OSSE PI teams have guaranteed rights to
the data from any Galactic supernovae, but exactly what data will be
obtained is not clearly stated. We would like to dedicate the
observatory to the observation of a Galactic supernova for several
months, but that might be impractical, so on behalf of the PI teams we
outline the desired observations of such an event.  

Cycle 4 CGRO COMPTEL and 0SSE observation of Cas A Supernova Rernuant

The recent COMPTEL discovery of the 1.16 MeV gamma-ray line of 44Ti
from the Cas A supernova remnant (SNR) is potentially very important
because it provides a calibration of the supernova nucleosynthesis
yield of 44Ti. The measured flux translates into ~2x10^-4 M0),
compatible (although on the high side) with explosive nucleosynthesis
calculations ~10^-4 M0). Furthermore, the detection demonstrates that
unobserved supernovae in the galaxy from the past several hundred
years are potentially detectable through their 44Ti gamma-line
emission.  0SSE in its one observation did not detect 44Ti emission
from Cas A. To confirm the C0MPTEL discovery, we propose a 6 week
joint COMPTEL and OSSE observation of Cas A. The purpose of this
observation are: 1. To confirm COMPTEL's detection of the 44Ti 1.157
MeV line by 0SSE and to study the accompanying lines at 68 and 78 keV.
2. To increase the statistics of the COMPTEL data, so that more
stringent constraints can be derived for the 44Ti mass and for the
width of the 1.157 MeV line. 3. To detect 40 keV (and harder) X-rays
using OSSE and the 12C and 16O nuclear excitation lines from cosmic
ray interactions in the SNR using COMPTEL and OSSE.  

COMPTON OBSERVATORY'S NEXT CLASSICAL NOVA

We propose to observe the next classical nova of each class,
carbon-rich and neon-rich, which is convincingly at a distance less
than 2 kpc. We will observe with OSSE for 3-4 weeks during the first
month after outburst to search for 478 keV gamma-rays from 7Be decay
and for a similar time with both OSSE and COMPTEL at roughly six
months after outburst. This latter observation is to search for 22Na
decay photons at 1275 keV when the entire ejected shell is undoubtedly
quite thin to gamma-rays. Because there is only roughly a 20 chance
per year of one acceptable event occurring, we optimistically submit
this proposal to cover the next five years.  

A SEARCH FOR RADIO-QUIET GAMMA-RAY PULSARS: ARE THERE MORE GEMINGAS?

We propose to search for radio quiet gamma-ray pulsars among the known
EGRET point sources. This investigation will utilize the significant
computational resources of the Caltech Concurrent Supercomputing
Facilities to calculate Gigapoint power spectra to search for
periodicity over a wide range of periods and period derivatives. Such
a search would have easily detected the pulsation of Geminga. We
request cycle 4 exposure to enable a search for Vela-like pulsation in
GRO J0004+73, GRO J1461-61, and GRO J2019+40; and for Geminga-like
pulsation in five other sources. Our investigation will include a
search for Geminga-like pulsation in two sources with archival data.

Imaging Blazars with the Comptel  Instrument

Both the COMPTEL and EGRET instruments on the Compton Gamma Ray
Observatory observe simultaneously with field-of-views aligned along
the same CGRO pointing axis. We propose to perform high sensitivity
imaging and, simultaneously, spectral analysis of EGRET blazars in the
0.7-30 MeV COMPTEL energy range. For the First time, the full
information contained in each Compton telescope event will be used.
The constrained linear algebraic deconvolution imaging technique
(CLAD), recently developed at UCR for Compton telescopes, will be
modified to also deconvolve the energy spectra of these sources at the
same time. This new method will permit the full COMPTEL energy range
to be divided into intervals that are more consistent with its energy
resolution. It is also particularly suited for sparse data sets and
combinations of data sets from different observation periods.  The
proposed research can potentially add significant insight to the
spectral shape and spectral variability of these core-dominated
gamma-ray sources and discriminate between various models.  

A Survey of Flat Spectrum Radio Quasars Near the South Galactic Poles
Filling in the Most Severe Deficiency in the Gamma-Ray AGN All-Sky
Survey

The unifying characteristic of all AGNs detected with the EGRET
instrument aboard the CGRO is their association with strong
flat-spectrum radio quasars (fSRQs), particularly those of the blazar
type. A thorough investigation of the properties of gamma-ray blazars
as a population requires identification and study of these objects
over the entire sky. FSRQs are uniformly distributed across the sky,
with approximately 40 located within 30 degrees of the SGP. Through
the first three phases of the mission, however, the cumulative
exposure of CGRO toward the SGP has been severely deficient. We
propose two 2-week pointings toward the SGP to carry out a search for
gamma-ray blazars with the EGRET and COMPTEL instruments. This program
would rectify the exposure deficiency, and contribute valuable data to
the sample available for the study of gamma-ray blazars as a
population. This investigation is designed to complement the blazar
campaigns organized by the EGRET team.  

INTERPRETING GAMMA-RAY BURSTS TEMPORAL STRUCTURE

The central question for gamma-ray bursts is whether they are at
cosmological distances with redshifts of ~1 or originate from galactic
neutron stars. We propose a very sensitive test (the average
auto-correlation) to measure the time stretching associated with
cosmological models. Preliminary simulations indicate we can measure
the time stretching to +/-1O%. Further, we have developed techniques
to interpret the time stretching in terms of the standard candle
luminosity it requires. We have unique PVO data that will provide
additional brightness classes and a check whether the time stretching
is intrinsic to the bursts or an artifact of the analysis. Our goal is
to determine if there is a redshift consistent with time stretching
and the Log N-Log P distribution.  

A Continuation of the Supernova Alert in Nearby IRAS Galaxies for the
Gamma Ray Observatory

We propose to continue our monthly patrol for supernovae (SNe) which
specifically targets galaxies where SNe might be detectable by GRO. We
use a near-IR detector to observe dusty IRAS starburst galaxies
(e.g. NGC 253 and M82) rich in massive, young SN progenitor stars. The
SNe occuring in these dusty regions are obscured to optical detectors
but are visible in the near-IR (and gamma rays!). Current models and
observations predict a higher near-IR SN detection rate than that
measured in optical bands. We expect to observe 1-4 SNe per year
within 10 Mpc, the limiting SNe detection distance for OSSE.  Six to
eighteen SNe are expected for our sample up to cz=2000 km/s, producing
a more accurate SN rate measurement than previously available. This
year we plan to build and deploy modest optics for optimum sampling of
our point spread function which will produce better SN detection
sensitivity, especially in bright galaxy nuclei. We will also begin
very frequent (weekly or more often) observations of a small sample of
the nearest galaxies.  

Study of Soft gamma Repeaters with BATSE

During the first 2.5 years of its operation, BATSE detected recurrent
emission from 2 of the 3 known SGR sources, SGR 1900+14 and SGR
1806-20. The reactivation of the latter prompted an immediate,
international campaign resulting in the identification of the x-ray
counterpart of the source, which also coincides with a compact radio
source.  So far, this is the only identification of the source of a
transient high-energy (>30 keV) phenomenon.  We propose to monitor and
analyze (temporally and spectrally) SGR emissions for at least 3
years, periodically reconfiguring BATSE to obtain better sensitivity
to SGRs. Our analysis will enable multiple source identifications and
lead to a better understanding of the phenomenon.  

0SSE Search for Line Features from the Crab Pulsar in the 400 to 500
keV Energy Range

The CGRO/OSSE has yet to observe the Crab pulsar vith full sensitivity
in the 400Ñ500 keV energy range. This 400Ñ500 keV energy range is
particularly intriguing as the reported line features in this energy
range have been attributed to the existence of a copious flux of
electron positron pairs that are produced by the Crab pulsar. The
existence of such a flux occurs naturally in many theories for pulsar
emission, hence the confirmation of the previous hints at the
existence of such lines could be an exciting validation of one of the
basic concepts underlying most pulsar emission theories.  Moreover,
the observed intensity of such a line can discriminate among different
theories for Crab pulsar energetic emission. To achieve significant
sensitivity we propose to stare with all four OSSE detectors for a
full 3 weeks.  

OSSE OBSERVATIONS OF GALACTIC BLACK HOLE CANDIDATES AND THEIR
NEUTRON-STAR IMPOSTORS

We propose a study with OSSE of galactic black hole candidates and
selected known neutron star systems which mimic their spectral and
temporal behavior. Our study will identify the charac-teristic
behavior which arises from the innermost, gamma-ray emitting regions
of accreting X-ray binaries; differences between the emission of
accreting black holes and the emission of nonmagnetic neutron stars
will likely come from this region. To isolate behavior unique to black
holes, we prc-pose to observe established black holes, known neutron
stars with similar observable properties, and suspected black holes
which lack mass determiriations. Our observational study should have
broad impact on our understanding of disk physics and the hot coronae
widely believed to exist in accretirig black hole systems.

OSSE Observations of the Galactic Center Region

We propose OSSE observations of the Galactic Center region (within 10¡
of the galactic center).  The purpose of these observations is
threefold: 1) monitor and study the sources in the region, 2) extend
coverage for determining the two dimensional distribution of diffuse
gamma ray emission towards the central regions, and 3) monitor for,
and locate any transient annihilation phenomena.  The proposed
observation plan would be comparable in scope to those completed by
OSSE in phase I, with a consistent, improved strategy that will
enhance their significance.  

Study of Pulsals at MeV Euergies

Comptel has detected pulsations from the Crab, Vela and PSR1509.  All
three pulsars have different light curves and spectra.  The
phase-resolved spectra are a key to understanding the production
mechanisms in pulsars.  We propose to make observations to increase
the statistical precision of the results already obtained, and to
search for time variability reported by COS-B at low-energies for Vela
and Geminga, and in the BATSE data for PSR 1509.  We also request the
right to follow up on any new radio-pulsar which may be discovered
within a cycle 4 field of view.  The accumulated data so far fail to
reveal Geminga.  Judicious pointing will put Geminga in the FOV with
Crab and may yet yield a significant detection.  We depend upon the
independent efforts of the radio ohservatories in continued monitoring
of Erab, Vela and PSR1509.  We request the right to analyse the
unpulsed components of Crab and Vela.  

0SSE 0BSERVATI0NS OF GALACTIC P0SITR0N ANNIHILATION RADIATION

Positron annihilation provides a unique and powerful mechanism for
increasing our understanding of the astrophysics of our Galaxy and its
chemical evolution. OSSE observations of the galactic plane and
galactic center region have provided the first measurement of the
distribution of the annihilation radiation. The 511 keV line emission
is found to be strongly peaked in the direction of the galactic center
and to consist of two separate components, a galactic disk component
and nuclear bulge component. The available observations of the
galactic plane, however, do not significantly constrain the
distribution or flux from the disk component. A more detailed study of
the disk component will provide information about the source of the
disk positrons and the physical properties of the annihilation medium.

OSSE MAPPING OF DIFFUSE GALACTIC GAMMA-RAY EMISSION

We propose a multi-year investigation to map the galactic plane using
OSSE. By the end of Phase 3, the galactic plane and Galactic center
will have been observed for over 250 days. Maps generated from these
data will allow the galactic diffuse emission to be studied with good
sensitivity and spatial resolution.  Both galactic nuclear lines and
the continuum spectrum will be observed.  The former are important to
understand the history and chemical evolution of the Galaxy. The
matter probes the galactic distribution of cosmic rays, magnetic
fields, and possible populations of unresolved point sources. This
project would continue the ongoing efforts of the OSSE Diffuse
Galactic Science Team, consisting of members representing both the
Instrument Team and the Guest Investigator community. This study will
also aid in the analysis of weak point sources of emission located in
the plane of the galaxy by reducing the uncertainty in the
contribution from the diffuse emission.  

PROMPT OSSE OBSERVATION OF BATSE BURST LOCATIONS

We propose, for Cycle 4 and beyond, to use the flexible OSSE pointing
capability to promptly (within minutes) observe the locations of BATSE
gamma-ray bursts using position information provided on-board by
BATSE, refined, in some cases, by ground-based analysis and data from
other instruments (COMPTEL, EGRET).  This will allow us to make the
most sensitive ever tests for post-burst emission in hard X-rays and
soft gamma-rays. OSSE will respond rapidly enough to observe the tails
of some long duration events, giving good spectra and improved
positioning along our scan plane. Given our field of view and the
BATSE event rate, we expect to respond to 1-2 events per month. This
will not significantly affect the normal scheduled observations.

Study of Gamma-Ray Emission from Radio Pulsars

We resubmit this proposal from Phase 3 as a renewal in order to secure
the observation of PSR 2334+61 which was classified as ÒAÓ target, but
whose observation was postponed until cycle 4. We propose to make
observations of gamma-ray emissions from pulsars with the OSSE
instrument on the CGRO. The pulsars to be observed are PSR 0656+l4,
PSR 1916+14, and PSR 2334+61. These pulsars were selected for their
ability to produce observable gamma-rays based on considerations of
particle acceleration and distance. Our model for gamma-ray emission
from magnetic Compton induced pair cascades in pulsar magnetospheres
makes several predictions.  Among these is that the hardness of gamma-
ray spectra at low energies (<100 MeV) should be correlated with the
ratio of the magnetic field strength to the pulsar period. We will
compare the results of these observations with the predictions of our
model.  

Target of Opportunity Vieving of Bright Transients from X-Ray Pulsars

We propose to observe bright transient outbursts of X-ray pulsars with
OSSE. These objects could be observed as Targets of Opportunity
folloving a strong outburst the total emission exceeding 1 total Crab
in flux in the 20-50 keV band, sustalned and rising over a period of
at least one day, as measured by BATSE.  OSSE observations provide
detailed spectral information and better sensitivity of the higher
energy emission, including separate measurements of phase-averaged and
phase-resolved spectra, than is possible using BATSE alone. In
addition, in view of the importance of characterizing the soft
gamma-ray emission of any net X-ray pulsars, we propose OSSE
observations of any newly-discovered pulsars in outburst > 50 mCrab in
the 20-50 keV band.  

GRO Observations of Bright Gamma-Ray Transients

We propose to observe bright transient sources with temporal and
spectral charac- teristics similar to those typical in potential black
hole candidates during cycle 4 of the Compton Gamma Ray Observatory
(GRO) mission.  These objects would be observed as Targets of
Opportunity (ToO) following outburst.  Detection of the out- burst and
monitoring of the light curve be provided by the Burst and Transient
Spectrometer Experiment (BATSE), whiIe spectral measurements will be
provided by the Oriented Scintillation Spectrometer Experiment (OSSE).
OSSE and BATSE measure timing noise over a broad energy range.
COMPTEL will extend spectral measurements up to several MeV, provided
simultaneous observations are achieved.

  
Multiwavelength Studies of Rotation-Driven Pulsars

The proposed work includes: (1) OSSE and BATSE observations of two new
pulsars discovered by us at Arecibo: an X-ray emitting pulsar
(J0631+10, EGRET obs. also requested) and a binary, millisecond pulsar
(J0751+18) found in the error box of an unindentified EGRET source;
(2) OSSE observations of two additional young pulsars, B1055-52 and
B1706-44; (3) radio searching for pulsars in error boxes of
unidentified EGRET sources and gamma-ray burst sources; (4) analysis
of radio pulse timing data and astrometric data in support of the GRO
pulsar observations; (5) interpretation of the results in terms of
current models of pulsar magnetospheres. Members of the BATSE, EGRET
and OSSE teams have agreed to work with us on items (1)-(3).  

A Toolkit for Modeling the Spatial/Intensity Distribution

We propose to create a public toolkit consisting of a suite of
subroutines designed to enable investigators to accurately calculate
the probability for obtaining the BATSE gamma-ray burst data given
some hypothesis for the distribution of burst intensities and
locations. This probabilityÑthe likelihood function - can be used to
test models for the burst distribution, including all known selection
effects and uncertainties. Its calculation requires significant
additional information beyond that currently available in the public
BATSE burst catalog. We propose to make two major improvements to the
catalog: 1) Calculation of an improved detection efficiency that
includes three important effects omitted in current calculations
spectral dependence, scattering of rays from Earth's atmosphere, and
Poisson uncertainties; (2) More precise quantification of
uncertainties in burst directions, including quantification of
asymmetries in the uncertainties which may be crucial for assessing
models that incorporate repeating burst sources.

HIGH RESOLUTION GAMMA RAY SOURCE OBSERVATIONS USING LUNAR OCCULTATION
OF SOURCES OBSERVED BY THE BATSE/GRO DETECTOR

We propose to develop a technique for high resolution hard X-Ray and
soft gamma-ray source location using lunar occultation technique in
conjunction with the BATSE detector.  The technique allows measurement
of source position with a resolution of about 2 arc seconds, a factor
of 300 imporvement in resolution over existing gamma ray detectors.
This analysis will use the occultation fit data set and DISCLA
accumulator channels to look for changes in count rates as individual
sources undergo lunar occultation. The analysis will first be
performed on archival BATSE data.  The technique can be also used to
monitor time variability (3-4 hours, and several months) of known
X-ray and gamma-ray sources as well as search for additional sources
in a band of the ecliptic.

Soft Gamma-Ray Emission from the Seyfert Galaxy  MCG+8-11-11

We propose a standard two-week observation of the bright Seyfert 1
galaxy MCG +8- 11-11, which was detected by OSSE above 100 keV in
Phase 1. The intent of this proposed observation is to accurately
measure the continuum shape and the cut- off energy, in order to
compare this vith the previous OSSE observations, with the goal of
testing Comptonization models for the continuum production by studying
the relation between flux and temperature.  Most models predict that
the temperature Wlll decrease for increasing compactness of the
source.  Coordinated observations vith ASCA will be attempted. The
simultaneous observation of the source in the X-ray and gamma-ray
bands wouId allow a powerful diagnostic of the physical conditions in
the Comptonization region and of the role of cold thick matter close
to the gamma-ray source.

Particle Acceleration in Active Galactic Nuclei

We propose to examine models of black-hole particle energization and
make a detailed comparison with data from the Compton Observatory in
order to test different acceleration and radiation models.  In
particular, we plan to analyze stochastic particle acceleration by
Alfvenic and whistler turbulence generated in the black-hole accretion
plasma. Preliminary results show that optically thin accretion-disk
coronae are produced in low luminosity environments, and collimated
relativistic particle jets are produced near supermassive black holes
by Eddington-limited fueling of the black hole. Thus the fueling rate
and black hole mass could account for the differences between the
radio-loud, hard gamma-ray spectrum ECRET blazars and the radio-quiet,
soft gamma-ray spectrum OSSE Seyferts.  We also plan to analyze
compactness constraints and the gamma-ray AGN size distribution using
the new Compton Observatory data.  

Structure and origin of the large-scale Galactic continuum emission

A principal objective of the COMPTEL instrument is to study of the
largescale Galactic continuum emission. Analysis of Phase I data has
already shown that the Galactic plane is detected with high
significance. The spectrum of this emission has been used to constrain
the interstellar cosmic-ray electron spectrum. The presence of other
components not related to the gas is, however, likely. The accuracy
and reliability of such analyses depends on deep and uniform exposure
coverage of the entire Galactic plane. The combined exposure from
Phases I, II and III is extremely non-uniform; we therefore propose 8
1 week pointings which cover regions which are particularly
under-exposed or for the models or which are of particular value in
model evaluation and for which more exposure would be advantageous.

A Detailed Multi-Wavelength Study Of The Centaurus A Region

The Cen A region has repeatedly been observed with Compton
GRO. Complete analysis of the COMPTEL data obtained during Phase I and
Phase II shows an emission region consistent with the position of Cen
A, but large enough to include a second possible gamma-ray source (1ES
1312.1-4221). The energy spectra obtained in the energy range 0.75 -
30 MeV change significantly between Phase I and Phase II. This
spectral behaviour and the large uncertainty in the location of the
emission region could be explained by a contribution of more than one
source to the observed emsion.  Simultaneous optical, X-ray and CGRO
observations are proposed in order to identify the objects
contributing to the emission of the Centaurus A region.  Here three
weeks of observations with all four Compton GRO instruments as part of
a multi-wavelength study are proposed.  

Study of Gamma- Emission from AGNs with COMPTEL

It is proposed to perform a COMPTEL monitoring of 10 AGNs from which
either definite MeV-emission has been detected or from which at least
hints for MeV-emission have been seen by COMPTEL. Most of these 10
objects are of the blazar type, discovered by EGRET. Included in the
monitoring program is also a continuation of the deep Survey of the
Virgo region, which was started in phase 3.  The objective of these
observations is to determine possible correlations between spectral
shape (e.g. spectral break position) and intensity, to determine the
duty cycle for the high intensity states of AGNs, to determine the
luminosity distribution of AGNs at MeV-energies, and to determine the
contribution of unresolved AGNs to the cosmic diffuse background
radiation.  In addition, it is proposed to search for MeV-emission
from those EGRET detected AGNs, which occasionally show very soft
high-energy gamma-ray spectra. The data rights from these objects are
requested, if they fall into the COMPTEL field-of-view, because
observations are requested by other proposers for other purposes.

44Ti Detected Supernova Remnant in Galactic Centre Region

The COMPTEL detection of the 300 year-old Cas A supernova remnant
confirmed 44Ti being created at the predicted yields in core collapse
supernovae. In addition to this source, COMPTEL has detected a
candidate supernova remnant in the Galactic centre region through its
1.157 MeV ensssion from radioactive 44Ti with its ~70  year decay
time. This is the first discovery of a previously unknown recent
Galactic supernova through gamma-rays. This newly discovered supernova
remnant at its position of 1=356, b=-10 is a unique opportunity to
study the exceptional nature of these events: The theoretical
expectations of a few supernova remnants in the Galaxy being visible
in 44Ti radiation may now approach confirmation. Therefore we propose
specific observations of this region to determine the location and
extent (from imaging with better statistics), and the age (from 1.157
MeV line position and width).  Such results will enable a more
confined search for counterparts in other spectral regimes, to study
the peculiarities of 44Ti producing supernovae. Two pointings at
slightly different offsets from the source are proposed to assess
systematic uncertainties.

26Al Emission from Supernova Remnants

The COMPTEL image of the Galaxy in 1.809 MeV emission from radioactive
26Al shows a ridge of emission along the plane of the Galaxy, with
several additional distinct emission features. COMPTEL has identified
the Vela supernova remnant as one of the apparent emission features
far off the Galactic centre region, establishing proof that core
collapse supernovae play a major role as Galactic 26Al sources.  The
ROSAT all-sky X-ray survey has revealed a significant number of
previously unknown supernova remnants, detected by the X-ray emission
from an extended shell heated by their interaction with ambient
interstellar medium. A preliminary correlation of the COMPTEL 1.809
MeV map with supernova remnant positions shows that for a large
fraction of the 1.809 MeV emission features suernova remants are found
in the vicinity. We propose to select candidate regions to clarify
such association. The prime regions selected for observations comprise
confined regions of 1.809 MeV emission, correlated to enhanced diffuse
X-ray emission, and located in areas of the sky with weak exposure
from phases 1-III.

26Al Emission Structure along the Galactic Plane

The COMPTEL image of the Galaxy in 1.809 MeV emission from radioactive
26Al shows a ridge of emission along the plane of the Galaxy, with
several additional distinct emission features. The classical models
for the 26Al sources in the Galaxy predict smooth emission models
rather than irregular emission, although the distribution models are
not settled. COMPTEL has identified the Vela supernova remnant as one
of the apparent emission features far off the Galactic centre region.
We aim to clarify the details of this and other apparent emission hot
spots in the COMPTEL image. We propose observations for specific
confined emission features with sharp gradients as opposed to extended
diffuse features. We have selected the most luminous and most
concentrated `hot spots' in the COMPTEL image; OSSE mapping of these
features provides an independent view with different systematics. We
propose observations for the emission features in the Vela region, at
the steep falloff in the first quadrant (l ~31 deg), at the bright
l~345 deg spot, in the Puppis region at l~237 deg, close to the
Galactic Centre, and in the Carina region.

Analysis of Clustering and Repeating of Gamma-Ray Bursts

Recently, we have found evidence that gamma-ray burst sources repeat
multiple times, on a time-scale of months.  If true, this
significantly constrains the range of allowed models and strongly
favors a Galactic origin.  Given the importance of these implications,
it is clearly imperative to test the repeating hypothesis further.
First, we will analyze the BATSE data using the second- and
third-nearest neighbour statistics as well as the nearest neighbour
statistic.  Second, we will use counts-in-cells and higher-order
correlation functions to probe the repeating signal and understand the
crucial effects of positional errors.  Third, we will use maximum
likelihood to find the fraction of burst sources that have repeated
and the distribution of burst brightnesses for the repeating sources.

Analysis and Modeling of Cyclotron Lines in the

The existence of harmonically spaced lines in the spectra of some
bursts and the success of the cyclotron scattering model in explaining
them is the strongest evidence that some gamma-ray bursts are
galactic, rather than cosmological, in origin.  Given the importance
of this implication, it is imperative to test the cyclotron line
hypothesis further. This we propose do.  First, we will continue our
development of rigorous statistical methods based on Bayesian
inference that address the key problems of establishing the existence
of spectral lines and of deterrnining the best-fit values and credible
regions for the physical parameters describing them.  Second, we will
continue the search for lines in the BATSE spectral data, using these
methods.  Extensive simulations and joint fits to the data from three
BATSE Spectroscopy Detectors (SDs) for burst GB930506 emphasize the
crucial importance for line detection of maintaining the SD gain
settings at the highest practical values (7-8 x nominal).  Third, we
will continue our assessment of the consistency of the Ginga and
Compton observations.  Fourth, we will develop the cyclotron line
model further, and exploit our experience in analyzing Ginga gamma-ray
burst data to confront the model with data from BATSE, if lines are
found.  

MONITORING HIGH-ENERGY EMISSION FROM TIME VARIABLE UNIDENTIFIED EGRET SOURCES

We propose Cycle 4 EGRET observations and BATSE monitoring of time
variable EGRET sources (UESs) near the galactic plane. The nature of
these sources is currently unknown and information provided by BATSE
will greatly help in the interpretation of these sources. We plan to
study the long time scale behavior of the hard X-ray emission from
time variable UESs by the standard Earth occultation and imaging
methods. We aim to discover possible periodicities and correlations
between hard X-ray and gamma-ray emission. Our program is relevant for
the study of a galactic population of binary compact objects emitting
time variable gamma-rays because of orbital modulation or time
variable circumbinary environments.  

GRS 1915+105: A SUPERLUMINAL SOURCE IN THE GALAXY

Using the VLA in the A configuration Mirabel and Rodriguez (1994)
detected one-sided radio jets coming out from the hard X-ray source
GRS 1915+105.  They have identified condensations moving at a rate of
0.02 arcsec/day which at the distance of the source implies motions at
1.2 +/-0.1 the speed of light. We propose a study of correlated radio
and gamma-ray observations to: 1) model the evolution of the
outbursts, 2) infer the nature of the source from its spectral
characteristics, and 3) search for pulsed emission.  No special
funding is requested to carry out this research.