CGRO Cycle 7 Approved Program Abstracts

GRO-97-083 BAND Previous studies of the evolution of gamma-ray burst spectra have generally relied on fitting sequences of spectra. These studies usually were confined to bright bursts and often lacked sufficient temporal resolution. We propose studies wh ich sacrifice spectral resolution for temporal resolution; our two techniques are the crosscorrelations between intensity lightcurves in different energy bands, and the energy correlation of pairs of counts. We wish to: determine whether spectral evolutio n changes during a burst; isolate the spectral evolution on different timescales; and search for short-duration, narrowband emission.
GRO-97-002 BARTHELMY We propose (1) to continue to operate the BATSE Coordinates Distribution Network (BACODINE), (2) to improve the GRB location accuracy of BACODINE & (3) agressively pursue new customers & modify the operation to meet new site-needs. BACODINE is a system that calculates GRB locations from the BATSE telemetry data in real time & distributes those positions to instruments to make multi-band follow-up observations of GRBs in real time -- less than 6 seconds. Our approach allows the making of mu lti-band observations of the GRBs while they are still in progress. BACODINE is providing a new tool for GRB research. The current BACODINE site instruments are setting ever more stringent upper limits at ever short time delays. The recent SAX observation s have shown that near-realtime follow-up observations are critical to counterpart identification. Continued operations will improve the these limits & allow for more counterpart identifications.
GRO-97-070 BASSANI We propose a multiyear project to continue our previous study of all active galaxies in the Piccinotti sample using BATSE. We intend to exploit the Earth occultation technique to search for emission in the 20-100 keV band from these bright galaxies. The sample represents the only unbiased and complete 2-10 keV survey of the sky down to a limiting flux of 3.1x10^(-11) erg/cm2/s. As such this sample has been used to construct the LogN-LogS relation as well as the luminosity function of activ e galaxies in the 2-10 keV band allowing a determination of the AGN contribution to the X-ray background. BATSE data from three years of observations have already been analyzed and here we propose to extend this by adding data after October 95. With the c ontinuous monitoring of this sample, BATSE can record both intensity and spectral information about the brightest objects. Spectral and variability analysis at high energies on these AGN will be performed.
GRO-97-040 BERTSCH The EGRET observations of the June 1991 series of flares provided spectral and temporal measurements of high energy gamma ray emissions up to 1 GeV, lasting hours after the impulsive phase. Spark chamber and energy calorimeter observations provided information on the spectrum of accelerated particles at the Sun, and on their interactions and confinement. We propose a multi-year study to analyze all EGRET data in the calorimeter and all spark chamber data when the Sun flares in the field of view. Targets of Opportunity are requested under specific circumstances outlined in the proposal.
GRO-97-148 BLOEMEN We propose to complete a deep COMPTEL exposure of the Orion/Mon region (2 x 4 weeks) to extend and improve upon our study of nuclear deexcitation lines. This proposal is an update of our Cycle-6 proposal, which was accepted and scheduled ( 9 weeks), but only 5 weeks of good data will become available because of a ToO observation and because of observations during the period of reboost activities in March/April 1997. We wish to reduce the strong asymmetry in the currently available exposure and obtain a set of observations that is less influenced by the Crab. These additional observations, in combination with available data, will allow us to map the complex in narrower energy bands and improve significantly upon our spectral analysis, which is crucial for determining the origin of the emission.
GRO-97-131 BRAINERD We propose a study of whether the BATSE gamma-ray burst E-peak distribution is a consequence of instrumental effects. Resolution of this question is vital for the development of new theories. The proposed study will resolve it by answering these two questions: are the observed E-peak values correct, and is the triggering on a gamma-ray burst sufficiently independent of E-peak to make the observed E-peak distribution an accurate representation of the physical distribution? We will answer th ese questions through the following methods: by folding model spectra through the BATSE DRMs and deriving both the detection efficiency and the observed E-peak as a function of true E-peak; by examining the E-peak distributions found for BATSE bursts dete cted under various triggering criteria; by examining the detection of soft sources such as SGRs and hard sources such as TGFs by BATSE; and by comparing the burst characteristics found by BATSE to those found by Comptel.
GRO-97-133 BRIGGS The BATSE team effort to find lines in GRBs has found 17 significant candidates in 118 bright GRBs. We propose the analysis required to determine the reality of these candidates: when multiple Spectroscopy Detectors observed a candidate, w e will analyze that data for consistency or confirmation; we will evaluate the significance of the candidates considering alternative, reasonable continuum models; and we will evaluate the significance of the candidates considering the large number of spe ctra that were searched. The goal of this project is to determine whether or not low-energy (below 100 keV) spectral features exist in GRBs observed by BATSE. After reaching a conclusion on the reality of the features, we will either set limits on the exi stence of lines or characterize the distribution of line parameters.
GRO-97-229 BUCKLEY Motivated by the recent discovery of a high level of 50-150 keV emission from the BL Lac object Mrk 501 coincident with a period of intense flaring at TeV energies, we propose two weeks of observations of Mrk~501 with the Whipple Gamma-Ray Telescope, OSSE, and the Whipple Observatory's 1.2m optical telescope. We also propose a target of opportunity observation of Mrk 421 when the TeV flux exceeds the flux of the Crab Nebula. The OSSE detection of Mrk 501 and PKS 2155-304, as well as the ha rd X-ray spectrum observed for Mrk 421 in its high state, imply that Mrk 421 will also be detected with OSSE. These measurements should determine whether the apparent extension of the synchrotron emission of Mrk 501 to 100 keV is always present, or only o ccurred as a result of the intense flaring in April 1997, and whether this feature is unique to Mrk 501. Measurements of spectral cutoffs in the OSSE and Whipple wavebands constrain the physical properties of the blazar jets. !
GRO-97-088 CARRAMINANA Among gamma-ray pulsars, PSR B1509-58 is unique, with its gamma-ray spectrum not extending beyond the MeV range. It provides a powerful test for models: the polar cap model naturally predicts a cut at a few MeV, through magnetic photon pro cesses; the outer gap model accomodates MeV emission as a synchrotron component. The fluxes measured by COMPTEL for PSR B1509-58 are particularly constraining and may turn out to be decisive for the physical intepretation. However, partly because of the s carcity of specifically aimed observations, the present signal to noise is still low: the only report from an individual observation comes from the only pointing at less than 10 deg of the COMPTEL axis. We propose to observe PSR B1509-58 for five weeks, t hree of them with the pulsar close to the pointing axis. The resulting data will be analyzed together with archive data, using contemporaneous radio ephemerides.
GRO-97-136 CATANESE We propose to conduct a Target of Opportunity Observation of a nearby X-ray selected BL Lac object with CGRO in coordination with the Whipple gamma-ray telescope and the Rossi X-ray Timing Explorer when the object is in a high state of emi ssion. Fifteen BL Lac objcets, not previously detected by the Whipple telescope above 300 GeV, will be monitored for high state activity by both the Whipple gamma-ray telescope and the RXTE All-Sky Monitor. The ToO would be triggered by observation of a h igh state in the >300 GeV emission as detected with the Whipple gamma-ray telescope, if it lasts for at least a one week period. This technique yielded spectacular results with Mrk 501. By requiring an extended high state before declaring the ToO, the pro bability that a flare will be detected with multiple telescopes is high. Such an observation provides an excellent test of blazar emission models.
GRO-97-075 COE The proposal requests any BATSE data recorded during outbursts from eight Be/X-ray binary systems. Observing time on the Infrared Space Observatory has been aproved as Target of Opportunity observations should any of these systems go in to outburst. Since all these systems are both IR bright and X-ray bright during these outbursts we seek matching data from BATSE. All these systems are also being monitored by us at near-IR and optical wavelengths.
GRO-97-094 COLLMAR The gamma-ray blazar PKS 0528+134 has been previously detected by COMPTEL several times. The source shows evidence for a time-variable MeV-flux and spectrum, and for a correlated spectra-intensity behaviour which was found by a combined an alysis of the simultaneous EGRET and COMPTEL data. During gamma-ray high-intensity (flaring) states observed by EGRET, a "harder" MeV-spectrum is observed than during gamma-ray low intensity (non-flaring) states. The combined, simultaneous COMPTEL/EGRET s pectra indicate these two states as well. The flaring state requires a spectral turnover at MeV-energies, while for the non-flaring state a simple power-law model is sufficient to describe the observed spectra. The observations are consistent with an addi tional spectral component showing up at MeV-energies and above during the gamma-ray flaring states. To further monitor PKS 0528+134, we propose to continue the COMPTEL observations (0.75-30 MeV) with a continous observation of! 4 weeks.
GRO-97-095 COLLMAR We propose to continue the COMPTEL observations (0.75-30 MeV) of the Virgo sky region with a continous observation of 4 weeks. The prime goal is to further monitor the MeV-behaviour of the prominent Virgo blazars 3C 273 and 3C 279 in spect rum and flux to derive informations e.g. on their spectral shapes at MeV-energies, on possible spectra-intensity correlations, on duty cycles of high intensity states, to provide the gamma-ray state for correlations with other wavelength bands, and to par ticipate in collaborating observations on both sources. Both blazars have been detected previously by COMPTEL several times, showing a time-variable MeV-emission. An additional goal is to substantiate the COMPTEL results (detections/indications) on furthe r MeV-emitting AGN sources located in this sky region. For 3C 273 an EGRET observation is proposed as well, to check its gamma-ray state (>100 MeV) in Cycle 7 which was found at record heights in Cycle 6.
GRO-97-152 CONNAUGHTON We propose to undertake a hard X-ray survey of 92 BL Lacertae objects using the source occultation method developed by the BATSE team. A previous study of a sample of Active Galactic Nuclei containing 4 BL Lacertae sources resulted in the detection of 3 of these sources at a greater than 4 sigma significance level, showing BATSE has the sensitivity to detect at least some of these weak X-ray sources. It is proposed to investigate the emission levels and spectra of both X-ray- and radio-sel ected BL Lac objects in an effort to examine hard X-ray differences, if any, between the two classes. Recent results indicate that BATSE is sensitive to certain soft X-ray-detected flares from BL Lac objects on time-scales of days. Detection of strong, ha rd flares in lower energy X-rays (e.g. by RXTE, SAX) will initiate a search for correlated emission in BATSE data.
GRO-97-228 CONNORS The COMPTEL team has been operating a Rapid Burst Response system, in collaboration with BACODINE and NMSU. We have provided 1-2 degree localizations of bright gamma-ray bursts within our field of view within roughly 10 minutes of burst on set. With a change in Instrument Ground Station hardware, we have an opportunity to upgrade our system to enable us to provide localizations within 1 minute of burst onset, under the best conditions. While maintaining our current capability until each upg rade is in place, we propose to: 1) port the current system to the new hardware, with some improvements, to reduce response time to 6-10 minutes from burst onset; and 3) streamline the procedure and software so response time can be as short as 1 minute fr om burst onset. This opens the way for the fastest ground-based telescopes to respond to 1-2 degree localizations while the high energy burst emission is still in progress.
GRO-97-156 COPPI We propose a two-week OSSE observation of the Galactic Black Hole Candidate Source Cyg X-1 as part of a co-ordinated, broad-band observing campaign involving OSSE, SAX, and XTE. The combination of OSSE and SAX, in particular, will yield a unique data set, providing simultaneous spectral coverage from 0.1 keV to over 400 keV with no no energy gaps and fairly good time resolution. Data of this type is crucial for understanding the physical conditions inside the gamma-ray emitting region of C yg X-1 and the relation of this region to the accretion disk of Cyg X-1 as a whole. With such data and the sophisticated emission codes we have developed, we can strongly constrain: (i) the geometry of the gamma-ray emission region, (ii) the origin of the soft photons which are presumably being Compton upscattered to gamma-ray energies, (iii) the presence of electron-positron pairs in this region, and (iv) the presence of a significant non-thermal population of electrons and/o! r positrons.
GRO-97-164 CORDES We propose (1) new OSSE/EGRET pointings for known radio pulsars that are ranked high according to our likelihood analysis on CGRO data; (2) folding of archived and new data using improved radio timing models developed by us; (3) a 3-day OS SE pointing to the Crab pulsar to monitor its pulse shape; (4) A global likelihood analysis on new and archived CGRO data to give a complete picture of spin driven pulsars in gamma-rays; this will include upper bounds as well as detections and will incorp orate radio polarization results that constrain orientation angles relevant to beaming.
GRO-97-231 DANIEL The supernova occurrence rate is a critical factor in the theory of nucleosynthesis. There are important systematic uncertainties in the rates derived from optical surveys, due to absorption and source confusion, such that those rates must be considered lower limits. Those problems are negligible for the gamma-ray emission from the Co-56 which is produced in a supernova explosion. Of the instruments on CGRO, COMPTEL is the most sensitive to this emission as shown by its detection of SN 199 1T. In a standard 14-day observation COMPTEL can detect a type Ia supernova out to about 10 Mpc and other types to about 3 Mpc. We propose to derive a rate or upper limit by searching all COMPTEL observations for Co-56 emission and determining the sensiti vity to such emission from each nearby galaxy in the field of view. To maximize the sensitivity measures must be taken to deal with instrumental activation background, particularly in data from the latter half of cycle three o! r later.
GRO-97-069 DEAN We propose a multiyear project to study a sample of 40 AGNs using BATSE as an extension of two successful CGRO guest investigations by the same team. The sample consists of 22 bright (detectable at 5 sigma or more) and 18 fainter objects. Priority should be given to the bright subset of AGN. The aim of the proposal is to enrich the database of extragalactic objects already detected by BATSE having as a final goal the production of a complete sample of AGN in the 20-100 keV band. The use of this database will both allow statistical studies of the high energy characteristics of AGN and also permit the determination of the LogN-LogS relation and the luminosity function at high energy. Thus measurements in the BATSE energy range will help dete rmine the contribution of AGN to the cosmic diffuse background. Furthermore, spectral and variability information on the brightest sample objects will also enrich our knowledge of the emission mechanisms and the size of the AG! N emitting region.
GRO-97-161 DENNIS We propose to conduct a comprehensive analysis of CGRO solar flare x-ray data. We have assembled for this purpose a team of scientists with expertise at all levels of the analysis process, from instrument characterization to data reduction and interpretation. The objective is to understand electron acceleration and transport in flares, and their relationship to space weather. An additional objective is to develop an early warning system for interplanetary particle events using the BATSE Co ordinates Distribution Network (BACODINE). We also propose to continue providing online access to the BATSE solar flare data for the solar physics community, as we have since launch.
GRO-97-194 DERMER The recently discovered high-latitude e$^+$-e$^-$ annihilation radiation feature towards the galactic center region poses several interesting astronomical questions. These include the sources of the positrons, for example, whether they are created by nucleosynthetic decay processes or black hole production; the mechanisms by which the positrons are transported to high altitudes and annihilate; the implications of these observations on the activity taking place in the central region of the Milky Way; and the relationship between our galaxy and galaxies with starburst or nuclear activity. We propose to examine these questions and produce model annihilation radiation maps which can be fitted to the observations of the galactic diffuse 0.511 M eV annihilation radiation. Studies of the line shape and spatial dependence of the annihilation line and continuum radiation will be made which can be used to analyze OSSE and high-resolution observations of this emission.
GRO-97-195 DERMER This is a renewal proposal to continue archival EGRET analysis of radio-emitting AGNs which have not been reported as EGRET sources. We have developed a new software package for extracting from archival EGRET data counts, exposure, and dif fuse galactic background maps which are suitable for co-adding. We have obtained preliminary results on co-added archival EGRET data of known radio-loud AGNs, selected on the basis of radio-spectral index, classification as a radio- or X-ray selected BL L ac object, and detection in the OSSE band. Other properties and source classes will also be considered. This research tests unification studies of AGNs on the basis of orientation. We will also continue to model spectral and temporal variability of radio galaxies and blazars which can be tested by correlated multiwavelength observations.
GRO-97-096 DIEHL COMPTEL measurements revealed a remarkable feature of 1.809 MeV gamma-ray line emission far away from the inner Galaxy in the Cygnus region: Here a unique calibration of nucleosynthesis models for the candidate 26Al source types appears po ssible, since the morphology and the object population is well known. COMPTEL Observations of the Cygnus region have been taken already, with a total of 41 days assembled from 27 pointings altogether. However, strong background variations between these sh ort observations and the frequently large off-axis angles of the region of interest severly limits the cumulative sensitivity. We propose to perform dedicated observations of the Cygnus region that minimize possible systematic background uncertainties thr ough contiguous observations of the region, but also account for second-order response impacts through systematic 'dithering' of the pointing. With these observations, we expect to separately identify emission from the Cygnus ! superbubble, and foregr
GRO-97-097 DIEHL COMPTEL measurements revealed a remarkable feature of 1.809 MeV gamma-ray line emission far away from the inner Galaxy in the Vela region, where a unique calibration of nucleosynthesis calculation for two of the advertised candidate source types appears possible: If the contribution from the Vela Supernova can be demonstrated to dominate the observed 1.809 MeV signal, core-collapse supernova yield calculations for this object need to reproduce the observed amount of 26Al. Additionally, the nearest Wolf-Rayet star to the Sun at <300pc distance should be at COMPTEL's detection limit if 26Al yield predictions are correct. COMPTEL Observations of the Vela region have been taken already, with a total of 96 days assembled from 10 pointings altog ether. So far, special pointing requests had been ignored, however, severely limiting the cumulative sensitivity due to large off-axis angles. We propose to perform dedicated observations of the Vela region that minimize possi! ble systematic backgrou
GRO-97-212 DINGUS The highest energy emission from gamma-ray bursts is very difficult to produce, especially for cosmological distances. Yet EGRET detects the brightest bursts. The EGRET upper limits as compared to extrapolations of Comptel spectral fits ar e consistent with all bursts having high energy emission. The average spectrum from 30 MeV to 10 GeV is fit by a power law of photon index -1.95+-0.25, and there is no evidence of any high energy cut off. Only 7 bursts have been detected above 30 MeV; how ever, EGRET has measured fluxes and spectra for 20 bursts above 1 MeV. Evidence of longer duration emission is seen in several bursts. Further observations are requested.
GRO-97-105 DIXON We propose to continue our study of high energy (E>30 MeV) Galactic point and diffuse emission via non-parametric (model independent) techniques. Non-parametric techniques provide an important complement to model-based likelihood analyses, yielding detailed spatial information about the flux distribution, and the potential for unbiased point source detection. We approach this study with two types of tools: data denoising, which attempts to remove photon counting noise in favor of statistic ally significant structure, and image reconstruction, which additionally tries to estimate the underlying flux distribution by inverting the instrument response. Further, we continue investigation of the use of overcomplete basis libraries, which, from ou r work in Cycle 6, show the potential for separating point and extended components without recourse to a particular model.
GRO-97-019 DUROUCHOUX GX 339-4 is a unique source, in that it presents behaviors belonging to both persistent and transient sources. Based upon our previous GX 339-4 observations, we propose a multi-wavelength follow up program. BATSE will provide continuous ob servations of the source, which will be correlated with ground based telescope in visible, mm and cm wavelengths.
GRO-97-110 ESPOSITO For many years it has been believed that the acceleration of Galactic cosmic rays is due to the strong expanding shocks fronts associated with supernovae and supernova remnants. Analysis of the EGRET data near the Galactic plane has reveal ed that at least seven supernova remnants are spatially correlated with unidentified EGRET gamma-ray sources and, of these, four have been shown to be consistent with a model of gamma-ray emission due to cosmic ray acceleration by supernova remnants. Thes e four remnants, plus one other, all exhibit 1720 MHz maser emission(OH) and are of the composite supernova remnant type. However, statistical limitations preclude unambiguous identification of the unidentified EGRET gamma-ray sources. We propose for: 1) A Target of Opportunity pointing of EGRET in the event of a Galactic supernova; 2) Non-exclusive data rights to 26 supernova remnants.
GRO-97-247 ESPOSITO The supernova rate in starburst galaxies has been estimated to be on the order of ten to twenty times the supernova rate in our Galaxy. If the dominant acceleration site of cosmic rays are supernova remnants then the cosmic ray density in starburst galaxies should also be proportionally higher. This implies that the diffuse gamma-ray emission from starburst galaxies can be used to directly estimate the cosmic ray density in these objects. Data from EGRET gamma-ray observations of the nearb y starburst galaxies M82 and NGC 253 for CGRO cycles 1 through 4 ( April, 1991 through October, 1995) has been analyzed using point-source likelihood techniques. The results of this analysis are upper limits due to low exposure. Further observations of NG C253 and M82 (increasing the exposure) are required in order to determine the properties of these objects.
GRO-97-135 FINGER We propose a systematic study of accreting X-ray pulsars using BATSE. The full sky will be monitored daily for pulsars with spin frequencies in the 2 mHz to 0.5 Hz range. Quick-look estimates of the fluxes and frequencies for all detectabl e pulsars will be provided on the world-wide web, and refined measurements will be provided in updates to the long-term pulsar histories currently available from the COSSC. We also propose specific studies of the persistent binaries Her X-1 and OAO 1657-4 15, and studies of transient pulsars. This work will be carried out as a collaboration between Caltech and BATSE/MSFC pulsar teams.
GRO-97-189 FINGER An outburst of > 100 MeV gamma-rays from the accreting binary pulsar Cen X-3 was recently reported by Vestrand, Sreekumar and Mori. Their epoch-folding analysis, which used pulse frequency measurements determined by us with BATSE data, sho wed that the EGRET emission was pulsed. We propose a search in archival EGRET data for pulsed emission from other accreting pulsars. For this search we will use pulse timing measurements from BATSE to coherently epoch-fold the EGRET data. We also propose further study of Cen X-3 to see if additional detection can be made, and to see if the pulsed emission is correlated with the torque or flux observed with BATSE.
GRO-97-154 FISHMAN Recent discoveries of extended x-ray, optical, and radio afterglow emission from GRBs raise the possibility that higher energy (hard x-ray and gamma ray) afterglow radiation may also be observable. Relativistic fireball models for GRBs pre dict significant afterglow emission as the expanding fireball interacts with the surrounding medium. It is proposed that four rapid re-pointing, target-of-opportunity observations be made during Cycle 7 of strong GRBs with all instruments of the Compton O bservatory to test this model and others.
GRO-97-044 GEHRELS The sky maps of the 1809 keV line emission obtained by COMPTEL have revolutionized our understanding of the origin of Galactic 26Al. However, a recent measurement performed by the GRIS spectrometer has revealed the existence of a significa nt fraction of the 1809 keV line emission that does not appears in the COMPTEL map. We propose an analysis of the COMPTEL data, taking into account the information from GRIS, to derive a new 1809 keV map that will better account for the "missing" flux. GR IS also detected a surprising broadening on the line which implies that much of the 26Al (>50%) is traveling at velocities of 500 km s-1. This fast 26Al should produce a latitudinal broadening of the 1809 keV line emission. We propose to study the origin and location of this high velocity emission using the new COMPTEL map.
GRO-97-160 GROVE We propose a scheduled, 4-week, OSSE observation of the Crab Nebula to address the following engineering and scientific issues: (1) Cross-calibration with COMPTEL, and (2) calibration of OSSE's pulse-shape discrimination efficiency in the current post-reboost, high-background conditions; (3) Time variability in the total Crab emission below 100 keV and above 1 MeV; (4) Hardening of the spectrum of the total Crab above 1 MeV; (5) Transient narrow lines near 75 keV from the pulsar.
GRO-97-169 GROVE We propose target of opportunity OSSE observations of bright (exceeding 1 Crab) transient emission from X-ray pulsars. Through phase-averaged and phase-resolved spectroscopy, we will address the following issues. (1) Search for complex spe ctral features, such as cyclotron lines and/or the emergence of an underlying hard component. (2) Determine the pulsed lightcurves and pulsed fraction as a function of energy. (3) Determine the spectral and pulse-period evolution through the peak and deca y portion of an outburst. This is a resubmission of an expired GRO Cycle 4-6 multiyear proposal that resulted in the discovery of a 110 keV cyclotron line in A0535+26 and pulsar phase lags durings bursts of GRO J1744--28.
GRO-97-218 HARMON We propose to continue the capability developed by our group, the BATSE Earth Occultation Team at the Marshall Space Flight Center, for the use of BATSE as a hard X-ray/low-energy gamma-ray all-sky monitor. BATSE is the only current instru ment that can perform this function. We will: 1) monitor daily the activity of strong sources in the 20 keV to 1 MeV band; 2) search current and recent data for new or recurrent transients; 3) develop a source catalog covering the first 5 years of occulta tion monitoring; 4) implement a Galactic plane imaging survey; 5) expand access to Earth occultation monitoring data for the astronomical community through the WWW; and 6) focus scientific efforts on the analysis of a sample of objects we detect using our occultation technique.
GRO-97-043 HARTMAN In order to improve our understanding of the physical processes in blazar jets, which can produce the large observed luminosities of high-energy gamma rays, we propose to implement Targets of Opportunity (ToO's) to observe gamma-ray emissi on correlated with exceptionally bright emission in lower frequency bands. The objects selected for consideration either have demonstrated previous bright flares in high-energy gamma rays, or are EGRET-detected and well-monitored at lower frequencies. A t rigger for a ToO could arise from an exceptionally bright and rising state in the optical, IR, or mm/submm band. In addition, we propose that a ToO extension be added to any CGRO blazar observation (regardless of PI) which shows the object to be in a very high gamma-ray state.
GRO-97-018 HARTMANN The first six years of observations by BATSE strongly indicated a cosmological origin of gamma-ray bursts (GRBs). This distance scale has now been demonstrated by a redshift measurement of an optical transient discovered through the accura te X-ray localization of GRB970508 by BeppoSAX. We propose the next step, to further support the distance scale to GRBs by searching for large scale cosmological structures in the large BATSE database. We consider angular and brightness studies. A specifi c high school outreach program would accompany this research effort.
GRO-97-046 HOEFLICH Observations of Type Ia supernovae prior to maximum optical light in the Virgo Cluster can provide a rigorous test of sub-Chandrasekhar models in which an outer layer of helium ignites giving rise to an early intense signal of Ni-56 lines at 0.74 and 0.81 MeV. This translates into one TOO per approximately 3 years. Early detection is critical for this test. Methods to enable the early triggering and to optimize the data collection and analysis are presented.
GRO-97-077 HURLEY Many more counterparts may be needed to obtain a coherent picture of GRBs in the post-BeppoSAX era. To facilitate this, we propose to reduce the sizes of about 80 BATSE burst error circles/year by up to two orders of magnitude by triangula tion with Ulysses, and send the results to the wide astronomical community via BACODINE. We will also triangulate a subset of about 30 strong bursts/year in a completely automated mode, with no operator intervention, with delays as small as half a day. Th e error boxes will be used for a wide variety of projects, from counterpart searches to statistical studies. Finally, we will augment the network by adding the NEAR spacecraft, which should yield a subset of about 50 bursts/year with 1'x10' error boxes. T he above-average estimated cost is due to the fact that this effort directly supports a large number of auxiliary investigations. It is, however, heavily leveraged by JPL support for Ulysses operations. This is a multi-year pr! oposal.
GRO-97-073 IYUDIN The COMPTEL telescope on board the Compton Gamma-Ray Observatory (CGRO) is capable of imaging gamma-ray line sources in the MeV region at a sensitivity of about $10^{-5}$ photons/(cm$^2$s). Among such line emission sources of interest an i mportant place is occupied by the classical nova, which could produce astrophysically significant fluxes of the \na decay $\gamma$-ray line at 1.275 MeV. The nova shell expelled by the thermonuclear runaway should be transparent to 1.275 MeV emission a fe w days after the nova explosion. On the basis of Phase 1 and 2 data COMPTEL derived an average 2 \sig upper limit for any neon-type novae in the Galactic disk of the order of 3 $\times$ $10^{-5}$ \cms (Iyudin et al. 1995). We are shure that we could do be tter, and for that reason we would like to propose ToO observations with COMPTEL for any classical nova with the distance $\le$1 kpc from the Sun, or with the visual magnitude m$_V$ $\le$4.0.
GRO-97-216 JOHNSON We propose scheduled OSSE observations of four blazars, and Target of Opportunity pointings in support of the EGRET multi-wavelength target of opportunity blazar investigations. Of the four scheduled pointings, we propose observations of P KS 0528+134 and 3C 279 in conjunction with the EGRET multiwavelength campaign for these objects and propose scheduled observations of PKS 0208 - 512 and 3C 273. Blazar observations in the OSSE and COMPTEL energy ranges provide the most compelling argument s for beaming from the gamma-ray observations, test models which predict the range of breaks in the spectra and the shape of the spectrum below the break, and test whether soft gamma rays lag or lead the harder gamma rays.
GRO-97-243 JOHNSON We propose multiwavelength X-ray/gamma-ray campaigns for IC 4329A and NGC4388, two archetypical gamma-ray - bright Seyferts of type 1 and 2, respectively, and for NGC 4151, the brightest radio-quiet Seyfert (type 1.5). The determination of their X-ray/gamma-ray spectra will test the unified AGN model (Antonucci 1993 and references therein), according to which Seyfert 1.5s and 2s contain the same intrinsic X-gamma sources as Seyfert 1s but which are seen through an optically thick obscuring torus (e.g., Krolik and Begelman 1988). The obtained spectra will then allow us to study the physical processes responsible for the emission as well as the contributions of Seyfert 1s and 2s to the cosmic X-ray background. The OSSE observations will be a ccompanied by simultaneous observations by XTE and ASCA, which will allow a determination of their X-ray spectra.
GRO-97-034 KAARET Transient episodes of hard X-ray emission from several X-ray bursters have been recently discovered. Hard X-ray emission is an effective diagnostic of thermal and non-thermal processes occurring in accretion disks surrounding weakly magnet ized neutron stars. We propose a target of opportunity observation using OSSE triggered by BATSE detection of a hard X-ray transient from one of five selected X-ray bursters. The OSSE observations will accurately measure the hard part of the spectrum (100 -400 keV) and place strong constraints on theoretical models of hard X-ray emission. This proposal complements our ongoing investigation of bursters with BATSE and a similar TOO program approved for XTE.
GRO-97-098 KANBACH Several unidentified EGRET sources are found with spectral and long term temporal characteristics that resemble those of middle-aged pulsars. Multiwavelength investigations of selected sources (X-ray, radio and optical) reinforce the impre ssion that they are gamma ray pulsars. The nature of these candidates will only be revealed in the future, either through ongoing identification efforts or ultimately through sensitive measurements with the next generation of gamma-ray telescopes. It is t hen of great importance to establish accurate pulsar ephemerides and parameters (eg. age, braking index)using in retrospect the EGRET database. This will only be possible if we maintain a regular sampling of the candidate sources over the times until the objects are identified. We propose to monitor the prime candidates during 1998 to secure the data for future pulsar analyses.
GRO-97-237 KINZER Measurement of the cosmic diffuse gamma-ray background (CGB) is one of the original proposed science goals of OSSE. OSSE provides a capability, unique now and into the forseeable future, to observe this fundamentally important radiation. F ailure to seize the opportunity to use this capability to measure the spectrum and the isotropy of the CGB would be a considerable loss to astrophysics. Brief proof-of-concept tests with OSSE show quite encouraging results. OSSE will be able to confirm an d possibly extend the spectrum in the 50 keV to one MeV range, and to measure any spatial anisotropy in the CGB with a potential sensitivity more than an order of magnitude better than previous work, and adequate to detect the expected anisotropy. The pro posed observation program includes pointed observations in 6 roughly orthogonal directions, two of which are correlated with the cosmic microwave background anisotropy.
GRO-97-238 KINZER Deep OSSE observations of the inner galactic ridge, configured with the long axis of the collimator parallel to the plane, have been made only in Phase 1. This type of observations is essential to understanding the multi-component galactic plane continuum over the 50 keV to 10 MeV range. The existing sparse set of such observations provide a much improved understanding of the spectral and spatial details of this region (e.g. Kinzer et al. 1997a,b,c,). However, many questions are raised by these results which can be answered by deeper collimator-aligned observations. Understanding the several spectral components, which follow two or more different longitude distributions, requires a systematic study of the galactic ridge in both longitude a nd latitude. The requested observations will reasonably complete the on-going multi-year positive longitude observation program for the inner galaxy at 0 deg. latitude, and will complete roughly 25% of on-going multi-year obse! rvation program.
GRO-97-039 KIPPEN An outstanding problem in gamma-ray burst research is the small number of well-localized events. As a result, little is known about the small-scale angular distribution of sources. We propose to accumulate a catalog of more than 500 burst locations, with total "error boxes" < 1 square degree in area, by combining BATSE measurements with Compton/Ulysses timing annuli. The large number and superior accuracy of the combined BATSE/Ulysses locations will allow us to investigate small-angle clus tering (either intrinsic or due to repeating sources) and to search for correlations with catalogs of known objects (e.g., distant galaxies and quasars) with substantially improved sensitivity over any previous, current or planned efforts. In the absence of significant self-clustering or galaxy correlations, we will be able to place constraining limits on burst recurrence scenarios (including time-dependent repetition) and limit the range of possible cosmological source distan! ces.
GRO-97-054 KIPPEN Years of BATSE observations, combined with the recent discovery of counterparts related to distant galaxies, strongly suggest that gamma-ray bursts originate at cosmological distances. Cosmological burst emission models share the common fe ature that they are highly constrained by the spectral and temporal properties of high-energy (~1 MeV and above) gamma rays, where relatively little is known. We propose to use the measurements of BATSE and COMPTEL to investigate in detail the high-energy component of burst spectra and the short time scales over which the high-energy flux varies. The advantage of using BATSE measurements for the bulk of this investigation is that many bursts with high count rates can be studied. COMPTEL will be used to co nfirm the accuracy of the BATSE high-energy measurements.
GRO-97-024 KOUVELIOTOU BATSE has produced a unique database on the bright black-hole candidates Cyg X-1, GX339-4, GRO J0422+32, GRO J1719-24, and GRO J1655-40; new transient black-hole candidates are discovered at a rate of about one per year. We propose to cont inue our successful study of the temporal (fast variability in a frequency domain of 4mHz to 30 Hz) and spectral (20 to 300 keV) behavior of all these sources over a wide range of luminosities and spectral states. Motivated by the fact that the latter thr ee sources are transients, we also propose to expand this study to include temporal analysis of transient sources detected with BATSE in the future. Our studies cover an energy range only barely explored and an unprecedented time span of months to years.
GRO-97-048 KOUVELIOTOU During the first 6 years of its operation, BATSE detected recurrent emission from two of the three known SGR sources, SGR 1900+14 (once) and SGR 1806-20 (thrice). The first reactivation of the latter prompted an immediate, international ca mpaign resulting in the identification of the X-ray counterpart of the source, which also coincides with a compact radio source and a rare type of a very luminous and massive blue star. Its third reactivation initiated a TOO with RXTE, which resulted in t he first unambiguous detection of "bunching" in SGR outbursts in the 2-60 keV energy range. We propose to monitor and analyze SGR emissions for at least 2 years, reconfiguring BATSE to obtain better sensitivity to SGRs. We expect to enable multiple source identifications and lead to a better understanding of the SGR population.
GRO-97-147 KUIPER The binary milli-second pulsar PSR J0218+4232 was detected as a high-energy 5-sigma source in the ROSAT HRI data. Indications for pulsed emission were seen in these HRI- and in archival PSPC data. It was noticed by Verbunt et al. (1996) th at an unidentified EGRET source 2EG J0220+4228 is positionally consistent with the pulsar; a timing analysis of the >100 MeV data yielded intriguing, but inconclusive results with pulsed signifances slightly below the 3-sigma level. A similar timing analy sis using now all available archival EGRET data shows an increased significance, while a phase resolved spatial analysis in broad energy ranges above 100 MeV showed a nice ON-OFF effect in the skymaps. So, 2EG J0220+4228 may be the first milli-second puls ar seen at gamma-ray energies, but further substantiation is needed. Here we ask for a deep EGRET exposure of at least 4 weeks in order to determine the nature of 2EG J220+4228.
GRO-97-190 KUNDU The Sun is an important laboratory for understanding particle acceleration processes which may operate in many other astrophysical contexts. Building on our previous research which has demonstrated that the MeV electrons form a distinct po pulation in solar flares, we propose to continue to compare data taken with CGRO/BATSE, which is primarily sensitive to < 200 keV electrons, with images of very energetic electrons in solar flares obtained using millimeter--interferometer observations. Th e BATSE data supply the time evolution and the energy distribution of the (primarily lower--energy) electrons which produce hard X--rays in solar flares, while the millimeter data supply the same information for MeV--energy electrons. We will study the pr oduction of MeV--energy electrons in solar flares and their relationship to the lower--energy electrons which produce the bulk of the observed hard X--rays, and use the results to constrain particle acceleration theories.
GRO-97-244 KURFESS A small scan-angle dependent background systematic effect has been found in the analysis of OSSE data. The magnitude of this effect is sufficiently small that it does not have a significant impact for standard OSSE observations which use 4 .5 degree background offsets. However, it is a consideration for observations which require larger background offsets (e.g. such as observations of the galactic plane), mapping observations, and observations which require one-sided background offsets. The scan-angle dependent background is due to the non-uniform spacecraft background which is produced by the cosmic ray and trapped particle environments. Following the recent reboost of GRO from a 425 km orbit to a 515 km orbit, the trapped proton environme nt from South Atlantic Anomaly passages has increased by a factor of 3-4. We propose OSSE observations, using unallocated time in the observing program, to calibrate the scan-angle dependent effect in the higher background env! ironment.
GRO-97-119 LAMB Studies of the angular distribution of gamma-ray bursts on small scales can place constraints on repeating and on the clustering of burst sources (and thus on the distance to the burst sources, if they are cosmological). Knowledge of burst positions, and the statistical and systematic errors in them, are crucial to these studies. We have developed a powerful likelihood method that allows us to inter-compare burst positions determined by various instruments. We have used this method to inte r-compare burst positions determined by BATSE and annuli in the current 3rd IPN catalog, and thereby to estimate the systematic error in the BATSE burst positions. We will redo our analysis using annuli in a revised 3rd IPN catalog. We will also inter-com pare burst positions determined by BATSE, COMPTEL, EGRET, Rossi XTE, WATCH-GRANAT, and the 3rd IPN.
GRO-97-060 LEISING This is a request for continuation into Cycle 7 as suggested by the Cycle 6 peer review and endorsed by the CGRO project. Only 3 weeks were actually scheduled and the first was bumped for a target of opportunity. We have assembled all nece ssary tools, include the latest COMPTEL map of 26Al in the region and the ROSAT map of the remnant. We await our first observations. We strongly request that the full complement of 10 weeks be carried out. Recognizing the difficulty of scheduling, we are willing to wait into Cycle 8 for this to be completed. Basically, our goals were and are to confirm the detection of 26Al emission from the Vela direction and to determine whether this 26Al is indeed from the Vela supernova explosion, to extend the measur ement of the compact nebular continuum to \sim1 MeV, and to improve the measurement of the Vela pulsar light curve and spectrum.
GRO-97-061 LEISING This multi-year Cycle 4 proposal was approved through 1999 and rated ``outstanding'' by that peer review. We resubmit this Target of Opportunity proposal to remind the CGRO project of the ToO criteria and to request funding if and when the se observations are carried out. No funding was required at the time of submission, but it is requested now as direct project funding for science analysis by these investigators as instrument team members is no longer available. We wish to keep the ToO cr iteria and requested observations as they originally were. Briefly, we proposed extensive observations of suitably nearby supernovae with the OSSE and COMPTEL instruments to further understand the nature and details of supernovae of Types Ia, II, IIb, and Ib.
GRO-97-062 LEISING This multi-year Cycle 4 proposal was approved through 1999 and rated ``outstanding'' by that peer review. We resubmit this Target of Opportunity proposal to remind the CGRO project of the ToO criteria and to request funding if and when the se observations are carried out. No funding was required at the time of submission, but it is requested now as direct project funding for science analysis by these investigators as instrument team members is no longer available. We wish to keep the ToO cr iteria and requested observations as they originally were. Briefly, we propose observations of suitably nearby classical novae with the OSSE and COMPTEL instruments to clarify the nature of the outbursts of both carbon-rich and neon-rich types.
GRO-97-187 LIANG In Cycles 4, 5, and 6, we have been performing spectral fitting and theoretical studies of the SGR bursts, and multiwavelength observations and modeling of the highly unusual quiescent counterparts from the millimeter through the infrared. We propose to continue this program in Cycle 7. We will use the data from the Cycle 6 bursts from SGR 1806-20 to perform detailed fitting with our Compton and synchrotron burst models. We request non-exclusive data rights to the BATSE data from any new b ursts in Cycle 7 from any of the SGR for our burst modeling program. We have, and/or will shortly obtain, impressive new high resolution near infrared spectra, complete far infrared spectra, and imaging at a number of wavelengths that we will use to clari fy the relationship of the multiple components to the source of the bursts of gamma rays.
GRO-97-208 LIANG This is a Compton Cycle 7 Guest Investigator proposal for the renewal of Cycle 6 grant NAG 5-3840. It concerns the modeling, analysis, and interpretation of gamma-ray burst (GRB) continuum spectral evolution data obtained by BATSE. This pr oject is an ongoing collaboration between Rice University and the BATSE instrument teams. Following the major developments of this past year, we will focus in Cycle 7 on spectral evolution properties that may bear on the multiwavelength (radio to X-ray) b ehaviors of GRBs and their afterglows, and also put potential constraints on their emission mechanisms and distance scale. This is the core research project of the group at Rice.
GRO-97-163 LINGENFELTER We propose to make a thorough analysis of the new, much more extensive COMPTEL, EGRET and OSSE data from the Orion-pointed observations of Cycles 5 and 6, using the Monte Carlo simulation programs,which we used to analyze the earlier data from Phase 1 and Cycle 4. Thorough analysis of this new data is essential in order to resolve the spacial distribution of the emission region and the spectral shape of the emission features, which in turn will enable us to much more tightly constrain the required energy spectrum and abundances of the energetic particles and also the ambient medium in which they are interacting and distinguish between possible emission processes and accelerated particle sources.
GRO-97-252 MACOMB While over 150 sources emit gamma-rays above 100 MeV, the nature of the gamma-ray sky above 1 GeV is less well understood. A catalog of gamma-ray sources based on photons with energies greater than 1 GeV has been developed from 4.5 years o f EGRET observations. Twenty six sources have identifications with objects seen at other wavelengths. Thirty are unidentified with nine of the 30 being new sources. There is some evidence among the unidentified sources for two luminosity classes. We propo se to extend our study of GeV gamma-ray sources using further archival EGRET data. A search for transient sources, variability analysis and spectral studies will be the new emphasis.
GRO-97-123 MALLOZZI The BATSE detectors have recorded the first observations of an unexplained terrestrial phenomenon: brief, intense flashes of MeV photons. These events, known as terrestrial gamma-ray flashes, must originate at altitudes above 30 km to be o bserved by the orbiting detectors. Approximately 65 events have been observed in the past six years. The most likely origin of these high-energy photons is bremsstrahlung from relativistic electrons from high altitude electrical discharges above thunderst orm regions. We propose to continue observations of temporal and spectral properties for production and publication of a catalog of these events. Temporal correlations with radio observations made at Palmer Station, Antarctica and spatial correlations wit h satellite images of thunderstorm regions near GRO during these events will be investigated, enabling verification and testing of proposed theoretical models of the atmospheric processes believed to be responsible for these u! nique observations.
GRO-97-009 MATTOX We propose to continue our study of the Geminga pulsar with a cycle 7 exposure. The unique contribution of Geminga to the study of pulsar emission mechanisms and spin-down demands ongoing observations by EGRET to refine its pulse ephemeris and improve the statistics of its pulse profile and phase-resolved spectra. A cycle 7 observation is crucial to a better understanding of the timing noise behavior of Geminga. This bears upon two very interesting questions: 1. A braking index of 17 +/- 1 is found through a coherent analysis of the 24 yr baseline provided by EGRET, COS-B, and SAS-2 observations. 2. The EGRET timing residuals appear to have a sinusoidal modulation that is consistent with a planet of mass 1.7/sin i M_earth orbiting Geminga at a radius of 3.3 AU. This cycle 7 exposure alone cannot possibly confirm the planetary hypothesis. However, it could serve to disprove it.
GRO-97-221 MATZ Recent observations of post-burst soft X-ray emission by BeppoSAX have demonstrated the importance of such detections both for counterpart searches and for understanding the physics of GRBs. The rapid decay of the flux (1/t or faster) make s prompt measurements critical. OSSE has the capability to respond very rapidly (<2 min) to burst positions calculated by BATSE on-board GRO. This is by far the most prompt pointed response by a high energy instrument (compares to ~6.5 hrs minimum with SA X). We propose to continue the operation of the BATSE/OSSE rapid burst response for 1--2 events/month with at least 12 hr observations of each burst. This will overlap with any SAX pointed response and is consistent with the known duration of soft X-ray e mission. A 12 hr slew produces no significant sensitivity decrease in the scheduled observations and requires no special or additional mission operations resources. We also propose to analyze any events serendipitously observe! d in the OSSE FOV.
GRO-97-223 MATZ After six years of successful operation in orbit, OSSE has surveyed a large fraction of the important hard X-ray point sources. Most future observations of hard X-ray sources can now be performed by XTE and SAX, enabling OSSE to be used fo r observations that it can do uniquely well. One of the most critical of these is the mapping of diffuse galactic continuum emission. With its high sensitivity and large but well defined field-of-view, OSSE has the capability of mapping the diffuse galact ic continuum over the energy range 0.05-1 MeV. Mapping techniques have been developed and applied to OSSE data which can achieve resolutions of up to ~1-2 deg. This proposal, a continuation of an approved Cycle 6 proposal, requests a sequence of observati ons which will be used to generate maps of the diffuse galactic continuum emission over the longitude range ~10-55 deg. These observations will provide improved sensitivity to diffuse emission over all previous and currently p! lanned missions.
GRO-97-220 MCCOLLOUGH We propose coordinated hard/soft X-ray, IR, and radio observations of the relativistic jet source Cyg X-3 in association with our monitoring and accepted observing programs with other spacecraft and observatories. Continuous daily monitori ng of Cyg X-3 has been done for over a decade in the radio and for over 6 years in the hard X-ray by BATSE on CGRO. Recent studies show a remarkable set of relationships between the hard X-ray, soft X-ray, and radio which are related to the formation of r elativistic jets in this system. BATSE LAD occultation data will be used for the hard X-ray component in this study.
GRO-97-236 MCCOLLOUGH We propose to finish the survey of the hard x-ray/gamma-ray emission from Supernova Remnants (SNRs) using BATSE occultation data started in cycle 5 and continued in cycle 6. The ability of BATSE to continuously monitor the entire sky allow s for a uniform study of a large group of objects measured with the same instrument and sensitivity. From 45 remnants surveyed 5 are detected and 11 remnants show possible emission and are still being analyzed. When finished we will have created a hard x- ray/gamma-ray emission catalog of SNRs from the BATSE data and where possible will differentiate between the various types of hard x-ray/gamma-ray emission seen from the SNRs. Equally important will be the establishment of upper limits for SNRs which do n ot show any emission. Particular effort will be taken to create spectra for the SNRs detected.
GRO-97-031 MCCONNELL We have recently generated the first all-sky map at 2.2 MeV using COMPTEL data from the first five years of the CGRO mission. The purpose of this effort was to search for sources of unshifted neutron capture radiation, as one might expect in certain binary accretion scenarios. Although generally featureless, the maps do show one point-like feature (provisionally designated as GRO J0332-87) at a significance level of ~4 sigma. There is no obvious counterpart to this source, based on standar d scenarios for 2.2 MeV emission. We therefore propose to obtain further observations to confirm the presence of this source using both OSSE and COMPTEL during cycle 7. In parallel with this effort, we also propose to continue work using archival COMPTEL data to refine our 2.2 MeV analysis methods (especially with regards to background modeling) and to incorporate additional data from later observations not included in the present analysis.
GRO-97-072 MCCONNELL Although observations of soft X-ray transients with CGRO have provided a wealth of information about the hard X-ray emission of these sources, observations of spectra near 1 MeV are limited. Based on experience with Cyg X-1, such observati ons would be valuable in our efforts to understand the high energy spectrum. Even a single significant datapoint near 1 MeV, when combined with lower energy data, could prove useful (c.f., GRO J0422+32). COMPTEL is capable of providing such data. Unfortun ately, past COMPTEL observations of XRTs are limited in number, and often so limited in exposure that no detection was possible. We propose long exposure observations with COMPTEL (perhaps in a low threshold mode) of any new XRT which becomes visible duri ng cycle 7 and which is likely to be detected by COMPTEL. We also propose to continue the analysis of archival COMPTEL data incorporating recent improvements in data analysis, especially with regards to spatial structures in t! he data.
GRO-97-053 MESZAROS Progress in understanding Gamma Ray Bursts is crucially dependent upon a close interplay between increasingly specific analyses of the data, including new multiwavelength observations, and increasingly realistic physical models which addre ss these data. We propose to calculate the spectral variability of internal shock models of GRB, and to compare the calculated light curves and spectral/temporal correlations with the available gamma-ray data. Building upon our succesfull fireball aftergl ow model, we will also follow the development of the fireball into its late stages, up to months after the event, and investigate the time behavior and variability of the emission at X-ray, optical and radio wavelengths. The predicted observational signat ures will be contrasted to the data from the various relevant experiments.
GRO-97-078 MITROFANOV We propose a large project to perform comprehensive studies of generic signatures of flux and energy spectral variability of gamma-ray bursts from the 4B and later BATSE data bases. The basic signatures will include the Average Emissivity Curves, Average Normalized Profiles and Average Energy Spectra both for the total burst sample and for different sub-samples selected by peak flux or duration. These signatures will be compared among the various samples to resolve any significant differen ces between them. Monte Carlo modeling will be used to exclude any biases from the average signatures and to make robust estimations of the significance of differences between them. Both model independent and model dependent transformations will be develo ped and applied to the observed signatures of bursts in order to characterize the "typical emission" in the co-moving frames of their emitting sources. Any effects requiring distance-dependent source evolution will be identifi! ed.
GRO-97-014 MUCH A prerequisite for a broad energy study with CGRO is the assessment of the absolute calibration uncertainty of the CGRO instruments or at least relative calibration between the instruments. A cross calibration of the instruments can be per formed by selecting suitable objects on the sky. Experience from previous analysis has shown that a dedicated calibration observation is required for this purpose. Therefore we propose a 4 week Crab observation where instrument configuration and pointing direction is optimized to allow proper cross calibration. This observation will help to resolve the inconsistency in the OSSE-COMPTEL cross calibration above 1 MeV. It is emphasized that instrument calibration issues, and therefore the results of this ana lysis, can impact many scientific conclusions.
GRO-97-049 MUKHERJEE We propose to carry out observations of PKS 0528+134 with EGRET, correlated with observations at longer wavelengths, to examine short time scale variations (1 to 3 days), which can be detected by EGRET only during bright flares. Such multi wavelength studies will help us to understand better the processes by which gamma-rays are produced in blazars. PKS 0528+134 has shown one of the highest fluxes in previous EGRET observations and exhibits extreme variations in its flux history. In the 199 3 March observations, PKS 0528+134 was seen to flare in gamma-rays by EGRET, with a flux level that was comparable to the Crab pulsar. We also propose to study the correlation between the spectral index and the flux of PKS 0528+134, during a flare.
GRO-97-176 MURPHY We have applied new techniques for analyzing intense solar flares to the OSSE data obtained from the 1991 June 4 solar flare to obtain new information about the accelerated-particle spectra and composition and about the ambient plasma at t he flare site. We propose to apply these same techniques to the three other large 1991 June flares that were well-observed by OSSE (June 6, 9 and 11) and, if funding permits, to other weaker flares. Among the specific areas of analysis we wish to study ar e: continuous ion acceleration vs. trapping; accelerated-particle composition, spectrum and directionality; electron vs. ion energetics; temporal variability of the ambient material composition; the photospheric 3He/H ratio; existence of pre- and post-fla re energetic ions; and flare-plasma temperature and density as deduced from the positron annihilation line and 3-gamma continuum.
GRO-97-005 NEMIROFF All known types of objects at cosmological distances have been seen to undergo a gravitational lens effect except GRBs. Given even conservative cosmological distance estimates for about 2100 BATSE detected GRBs through Cycle 7, there is ab out a 25 percent chance of finding a gravitational lens effect caused by the known galaxy field. Precise timing information for GRBs carries enhanced information about the lens masses as well as general cosmological parameters. Our search for lensing, how ever, also encompasses a search for a cosmological abundance of dark matter from the scale of 1E-15 to 1E9 solar masses, including a planetary mass range unavailable to other methods. Previous CGRO lens searches led by the PI have yielded interesting publ ished limits and software that can be used in a Cycle 7 search. In addition to continuing past searches, we propose adding a ``real time" search designed to catch lens candidates within a week of being detected.
GRO-97-125 NOLAN The unidentified EGRET source 2EG J1835+5919 is bright and well localized. There is no convincing evidence for variability. It has never been observed well by EGRET. We propose further observations to settle the issue of variability, to im prove the search for pulsations, and to archive data in case it is discovered to be a pulsar by observations in another wavelength band.
GRO-97-082 NORRIS Recent detections of apparent gamma-ray burst (GRB) counterparts in optical and radio wavebands strongly favor the cosmological distance scale, at least for some GRBs, opening the possibility of GRBs serving as cosmological probes. But: GR Bs manifest great diversity; moreover, there are the possibilities of a luminosity distribution and evolution of average GRB characteristics with cosmic time. Given the sparse information at longer wavelengths for some time into the future, the ONLY viabl e approach to constraining GRB diversity, e.g., as a function of peak flux, necessarily involves use of GRB data. We will address the fundamental question of degree of GRB (non)uniformity by applying our automated pulse-fitting algorithm to determine micr o and macro GRB temporal/spectral characteristics as a function of GRB peak flux, thereby constraining the use of GRBs as cosmological probes.
GRO-97-150 OTTERBEIN We propose to observe the ultraluminous blazar S5 0836+710 with EGRET in the gamma-ray regime and at other wavelengths. S5 0836+710 shows pronounced outbursts of its flux in the high energy regime (optical/x-rays/gamma-rays) most probably related to variations at lower frequencies (radio/mm) and to the ejection of new jet components. In addition, short term gamma-ray variability is indicated during states of lower activity. Previous multifrequency studies of blazars showed that a variety o f quite different models is capable to explain the overall spectrum of the objects. Crucial tests to these models ask for time delay mapping of the outbursts throughout the spectrum. Dense sampled observatons in frequency and time settle stringent constra ints on the models.
GRO-97-199 PACIESAS We propose to produce a comprehensive set of catalogs of BATSE gamma-ray burst spectra that will be of general use to the astrophysical community. The catalogs will make use of the wide range of BATSE data types and allow convenient access to deconvolved spectra and corresponding model functional fit parameters with various combinations of time and energy resolution. The catalogs will be made conveniently accessible via the World Wide Web and will be updated regularly as new burst data com e in.
GRO-97-183 PARK We propose to search for simultaneous gamma-ray burst(GRB) optical counterparts using a wide-field-of-view telescope system that is connected to the Gamma-ray Coordinate Network (GCN). LOTIS (Livermore Optical Transient Imaging System) is an automated telescope system that views a 17.6 x 17.6 deg field of view, is sensitive to Mv ~14 and responds to a burst trigger within 10 sec. The system has been operating since Oct. 1996 and has recorded many GCN triggers, some while the bursts were st ill in progress. We propose to further enhance this system to be sensitive to Mv ~ 16 and construct a 50 cm aperture system that matches the new GCN notices with smaller errors (LOCBURST and RXTE triggers). A simultaneous detection and the production of t he realtime GRB light curves will greatly enhance our understanding of GRB physics.
GRO-97-121 PENDLETON Recently we have identified two types of pulses in gamma-ray bursts (GRBs) that exhibit significantly different luminosities. Emission pulses in GRBs that show a marked lack of fluence above 300 keV appear to be 10 times less luminous than emission pulses with high energy flux. Some bursts show both types of pulses indicating that one source object is capable of producing both types of emission. We propose to perform detailed studies of the admixture of these pulses in GRBs to refine our a bility to detect cosmological signatures in the burst data, and to provide observational characterization of GRB emission that will be important for theoretical modeling.
GRO-97-126 PENDLETON Recent developments in burst counterpart identification makes the rapid production and distribution of accurate burst locations particularly important. We propose to implement some of the location algorithms from the Hunstville location co de LOCBURST in the BACODINE location code so that locations with 2 degree accuracy can be produced within 10-20s of the burst trigger for around 30 bursts per year. These locations will allow automated search projects to perform deep searches of burst loc ations at other wavelengths while the longer bursts are still in progress.
GRO-97-202 PERLMUTTER Despite reports of gamma-ray burst (GRB) related optical transients (OTs), the origin of GRBs remains unknown. To understand the physics of GRBs, further observations by all types of instruments are indicated, requiring rapid, accurate GRB positions. This project probes a new region of parameter space in the search for GRB images and positions by making sensitive (V>17.7 mag in 10 sec) optical measurements during gamma-ray emission and after. Our instrument, the Automated Patrol Telescope (APT; a wide-field, rapid pointing, 0.5 m aperture, CCD instrument), has already responded to GRBs 970326.6 and 970329. On receipt of a BACODINE alert, the APT interrupts its observations and acquires images starting ~ 20 sec after the GRB trigger. Rapid, automated reduction provides OT coordinates up to several hours before Sax, increasing critical setup time for other specialized observations, and providing independent alerts to compliment and verify Sax results.
GRO-97-036 PETROSIAN We propose to test the cosmological models for GRBs using their logN-logS relation and distributions of durations and spectra. Most previous analyses have dealt with some measure of peak flux, but models and recent multiwavelength observat ions indicate that the fluence is a more fundamental parameter. We have developed methods to account for the detection bias of BATSE fluences. We propose to compare the LogN-LogS distributions of the peak flux and the fluence and their correlations with b urst duration and spectrum. Our preliminary results show some paradoxical behaviors and indicate that by this method, especially with the inclusion of spectral biases and dispersions, we can provide answers to some important question: Is the total energy or the peak luminosity a standard candle? What are the relations of this standard with the durations and spectra? Are there two populations of GRBs with different durations and spectra?
GRO-97-087 PETROSIAN We propose to analyze BATSE and EGRET data on solar flares to test the stochastic acceleration model of the the impulsive phase, where plasma waves or turbulence arising from the energy release process play a major role. We have shown that this model can explain the details of the spectral deviations from a simple power law of two electron dominated flare. The scattering by the turbulence can also trap the particles in the acceleration region giving rise to bremsstrahlung X-rays observed b y YOHKOH from these regions. Combining these observations, not necessarily on the same flares, we can further constrain the model. We also propose to use the same model for acceleration of protons and compare the combined bremsstrahlung and nuclear line e mission spectra observations when the emission is not dominated by electrons. The large dynamic range provided by combined BATSE and EGRET data is crucial and can provide strong constraints on the model parameters.
GRO-97-168 PHLIPS We propose a target of opportunity observation of Cygnus X-1 with OSSE and COMPTEL when it becomes very weak as measured with BATSE, while at the same time not increasing its low energy X-ray flux, as measured by the All Sky Monitor (ASM) on RXTE. We consider this to be the definition of the state of Cygnus X-1 when enhanced MeV emission was detected during the HEAO-3 mission. Until the launch of RXTE, there was no way to differentiate between the source going in the known X-ray high, gamm a ray low state, and a potential rare state of X-ray low, gamma ray low emission. The observation would be contemporaneous with an XTE target of opportunity observation and possibly USA observations. The primary goal of this proposal is to confirm the exi stence of the MeV emission if the source goes in the defined state. By acquiring simultaneous spectra over the X-ray and gamma ray band, a data set would be available to test models of MeV emission and other black-hole models.!
GRO-97-111 PREECE Roughly 15% of bright gamma-ray bursts exhibit excess low-energy emission, based upon spectral fits of time-averaged BATSE Spectroscopy Detector data. We propose to determine the detailed time behavior of this excess. This can be done with BATSE archival and Cycle 7 data, by performing a series of spectral fits throughout the time history of bursts showing an excess. We wish to determine whether or not the X-ray component exists independently of the gamma-ray spectral history. The answer t o this question has direct bearing on the verification of theoretical burst emission mechanisms that have been recently proposed.
GRO-97-209 PURCELL OSSE is the only operating satellite instrument with the capability for studying the detailed distribution of galactic positron annihilation radiation. Recently, an asymmetry in the latitude distribution of the 511 keV line has been report ed based on mapping and modeling results using data from OSSE, SMM and TGRS. This exciting result, which was the product of a multiyear effort to develop mapping capabilities using the OSSE instrument, shows an enhancement of 511 keV line emission extendi ng up to ~7-10 deg above the GC. Another weak enhancement near (-9,-5) is also suggested. A better determination of the positron source requires an improved understanding of the distribution of the annihilation radiation. The proposed observations will: 1 ) better determine the size, shape, centroid and flux of the nuclear bulge component, 2) constrain the latitude width of the plane component, 3) more optimally study the latitude asymmetry, and 4) improve the sensitivity to ot! her enhancements.
GRO-97-214 PURCELL OSSE is the only operating satellite instrument with the capability for studying the detailed distribution of galactic positron annihilation radiation. Recently, an asymmetry in the latitude distribution of the 511 keV line has been report ed based on mapping and modeling results using data from OSSE, SMM and TGRS. This result, which was the product of a multiyear effort to develop mapping capabilities using the OSSE instrument, shows an enhancement of 511 keV line emission extending up to ~7 10 deg above the GC. The exact morphology of this ''fountain'' is not yet known and it is not clear if this feature is directly associated with activity in the GC region, although it is interesting to note that similar asymmetries are seen in radio map s. The proposed observations will: 1) better determine the location, morphology and flux of the enhancement, 2) provide a dataset from which a spectrum of the enhancement can be generated, and 3) significantly improve on curre! nt maps of the GC region.|
GRO-97-113 RAMATY We propose a new determination of the photospheric He-3/H based on the time dependencies of the 2.223 MeV line and prompt nuclear deexcitation lines. Using this method, the photospheric He-3 abundance was determined previously from SMM/GRS data. Since then longer duration and more precise OSSE data became available from the 1991 June 4 flare. In addition, we have updated the nuclear cross sections and the Monte-Carlo codes, and placed constraints on the various factors that could affect th e determination. Our proposed work will lead to a much more accurate determination of the photospheric He-3 abundance, greatly improving on the commonly employed approach which assumes that the photospheric He-3/He-4 equals the solar wind value for this r atio. The photospheric He-3 abundance is a key parameter in the study of galactic evolution, and has major implications on cosmological models as well as on the problems of the solar wind and solar flare particle acceleration.!
GRO-97-213 RAY We propose to make a two-week observation of the bright, extremely variable, high-mass X-ray binary system 4U 1700-37 with the OSSE instrument. We will conduct simultaneous X-ray observations with the USA Experiment aboard ARGOS. We will f it the hard X-ray spectrum above 50 keV to look for a spectral cutoff, absorption lines, and spectral variability with greater sensitivity and spectral resolution than previous observations. The concurrent X-ray observations will also make it possible to measure the temporal correlation between the hard and soft emission and better distinguish between spectral models. We will also perform a sensitive search for pulsations taking into account the measured orbital parameters of the system. We hope to shed s ignificant light on the nature of the compact object in 4U 1700-37, and the origin of its aperiodic flaring behavior.
GRO-97-144 ROBINSON We propose coordinated hard/soft X-ray, IR/optical and radio observations of the Galactic superluminal jet sources GRS 1915+105 and GRO J1655-40 in association with our accepted ASCA, HST, ISO, RXTE, SAX, VLA, VLBI and other ground-based p rograms. Continuous daily monitoring of these sources in radio, soft and hard X-ray bands has only existed since Nov. 1996 and permits observing outbursts from their initial states, determined by BATSE and/or radio flares, back to temporary quiescence. Th ese remarkable objects provide, due to proximity and much shorter dynamical timescales, relative to AGN, an exceptional opportunity to study jet formation, ejection and propagation into highly relativistic jets. As important, these systems provide probes of accretion and high energy radiation exceptionally close to their suspected black hole primaries. BATSE LAD occultation data will be used together with near-face-on pointings of GRS1915+105 to any one of the 8 BATSE SDs.
GRO-97-217 RYAN One of the principlal goals of the COMPTEL mission is to study the Cosmic Diffuse Gamma Radiation. A preliminary CDG spectrum has been reported earlier. The preliminary results suggests a lower spectrum than pre-COMPTEL estimates. Our goal is to derive the spectrum with finer energy bins and investigate any possible spectral features. We want to decrease the error bars by analyzing additional data and study the continuity of the COMPTEL spectrum with higher and lower energies.
GRO-97-227 RYAN We propose to continue and refine our studies of microflares using BATSE LAD data. We use an automated search algorithm to detect smallest X-ray bursts. We have searched the archival data for bursts into 1994. The output of this search is a microflare database that can be made public. With improvements in our search algorithm and our choice of selection criteria to exclude spurious events and with the new result that events are not fully accounted for in the BATSE low-energy channel (R. Sc hwartz, priv. comm.), we propose to reprocess the entire BATSE solar microflare database. This will result in a more uniform and predictable response among detectors to identify solar events and will also result in a better sensitivity for small flares. I t is important to start this process soon to catch up before the onset of solar maximum.
GRO-97-063 SCHOENFELDER A principal objective of the COMPTEL instrument is to study the large-scale Galactic emission, both diffuse and from discrete sources, and in both continuum and lines. Full sky images based on Cycle 1-5 data have already shown that the Gal actic plane is detected with high significance. The accuracy and reliability of these analyses depend on deep and uniform exposure coverage of the sky. The combined exposure and quality of data from Cycles 1-6 is extremely non-uniform even in the Galactic plane, especially considering angles near enough to the COMPTEL pointing axis which have the best quality for imaging analysis. We therefore propose a comprehensive set of pointings designed to yield a minimum effective exposure of 30 days within 20 degr ees of the Galactic plane for angles up to 25 degrees from the COMPTEL pointing axis.
GRO-97-177 SHARE One of the most startling discoveries made by the Compton Observatory has been the detection by COMPTEL of 3 - 7 MeV emission from the Orion Nebula. The emission appears to be spatially extended and its spectrum suggests some form of broad ened line emission, especially near 4 MeV. As the implications of this discovery have significant impact on several areas of astrophysics, it is essential that another experiment confirm the detection. Previous OSSE limits are consistent with the COMPTEL fluxes for an extended source. The OSSE spectra also exhibit a weak (1.4 sigma) line feature near 4 MeV with an inferred flux consistent with the COMPTEL observation. We propose a six-week OSSE exposure for each of the next three years, concentrating on a broad ridge of emission suggested by COMPTEL, in order to confirm the emission. We also suggest an alternative, and possibly more sensitive, approach for detecting the broad 4 MeV line that can be applied to all observations.!
GRO-97-179 SHARE The Sun is embarked on Cycle 23 and its activity will rise markedly over the next year. OSSE is the most sensitive spectrometer in orbit for making nuclear line and continuum measurements. We propose a plan for making comprehensive observa tions of the Sun during this new Cycle. We propose that OSSE observe the Sun on the X-axis for all observing periods without an approved X-axis target, that are compatible with the Z-axis observation. Under this proposal we anticipate that OSSE will have Solar exposure for up to 30% of the observing periods in the next few years. We also propose a Solar Target Of Opportunity with two levels of response: 1. OSSE slews to the Sun in response to a BATSE Solar trigger when it lies within 15 degrees of the tra ns-scan plane; 2. The Sun becomes an OSSE X-axis target when the probability of a GOES X-class flare during the next 48 hours exceeds 20%. This is a multi-year proposal with a cost of up to $70K/year, dependent on the number o! f solar observations.
GRO-97-012 STEINLE In this joint proposal by all CGRO instrument teams, a target of opportunity observation lasting four weeks with all four CGRO instruments is proposed to measure the spectrum of the nearest active galaxy Centaurus A in a state of strong ga mma-ray emission. Observations of Cen A in the whole energy range covered by CGRO at such a historically common, high intensity level, which has not been observed by CGRO so far, would provide greatly improved observation precision. They would provide tes ts of hypotheses concerning intensity-dependent spectral evolution which were advanced to explain the low and intermediate intensity level observations made so far with CGRO. A similar proposal had been accepted for Cycle 6, but Cen A did not brighten abo ve the threshold set.
GRO-97-155 STRICKMAN The presence of a hard X-ray tail from the bright low-mass X-ray binary Sco~X-1 has long been a source of controversy. We have recently detected a hard X-ray tail from Sco~X-1 using OSSE on CGRO. We now propose to study the behavior of thi s tail in more detail with a longer OSSE observation, performed in conjunction with a multiwavelength campaign. We plan to learn more about the morphology of hard X-ray variability from Sco X-1 and how it correlates to behavior at other bands. Using this information, we will interpret the data in the light of a number of models that currently predict hard X-ray emission from low-mass X-ray binaries.
GRO-97-153 SVENSSON ASCA observations show that the Seyfert 2 galaxy, the Circinus galaxy has a very flat 2-10 keV spectrum indicating a possible dominance of a reflection component. Estimates of the expected OSSE-flux show that the Circinus galaxy should be at least as bright as the Seyfert 1 IC 4329A, and possibly as bright as the second brightest Seyfert, NGC 4945. The Circinus galaxy has never been observed at energies > 10 keV. Being expected to be one of the brightest Seyferts in the hard X-ray, this ga laxy lends itself for detailed spectral studies. We possess unique tools to make physical (rather than empirical modelling) of broad band X/gamma spectra of Seyferts.
GRO-97-085 TAVANI Recent EGRET detections of unidentified variable gamma-ray sources near the Galactic plane opened a new field of investigation. We propose to study new gamma-ray transients with no % apparent radio-loud blazar-like counterparts (GRTs) loca lized near the Galactic plane. The nature of these sources (Galactic vs. extragalactic) and the mechanism of high-energy emission is currently unknown. We request non exclusive EGRET, COMPTEL and BATSE data rights for all GRTs of gamma-ray flux above 10** {-6} ph./cm**2/sec within +/- 30 degrees of Galactic latitude, and exclusive data rights for the first two GRTs in Cycle 7. EGRET quicklook analysis will be used to trigger rapid follow-up multiwavelength studies. We will request a GRO TOO observation in case EGRET detects a new GRT of flux above 2 x 10**{-6} ph./cm**2/sec.
GRO-97-059 THE Cycle 1 to Cycle 3 COMPTEL measurement has shown that its 1.157 MeV gamma-line sensitivity is 3-4x more sensitive than the instrument previously used to measure the Galactic Ti44 line flux. This improved sensitivity means that COMPTEL can probe the decays of Ti44 133 yrs further back in time than the SMM and HEAO 3 or probe distance 2x deeper to put a strong constraint on the analysis of the SN rate and Ti44 yield. This sensitivity will be further improved with the data from Cycle 1 to Cyc le 6. We propose to produce the maximum likelihood map of Ti44 line from Cycle 1-6 COMPTEL archival data and analyze it with Monte Carlo simulations. Combining this gamma-ray data with the six historic supernova recorded in the last milenium, the Ti44 yie ld, and the best available Galactic extinction model, we will be able to produce sets of parameters that represent the best of the given constraints.
GRO-97-027 THOMPSON In order to extend the life of EGRET, the gas in the spark chamber was allowed to deteriorate more than was originally planned for the nominal two year Compton Observatory mission. Gamma ray events are lost because the pattern recognition software and analysis rules are not optimized for the poorer quality data. By developing improved software and changing the rules used by the data analysts, we can recover a significant fraction of the lost events, allowing improved statistics for detecti on and study of sources. These changes can help all users obtain maximum scientific return from the EGRET data.
GRO-97-030 THOMPSON EGRET has measured the high-energy characteristics(E $>$ 10 MeV) of a number of gamma-ray bursts, principally those bright bursts appearing in or near the EGRET telescope field of view. In some cases, the high-energy emission has been obse rved to last as long or longer than the emission observed by BATSE. EGRET has collected spectra in the energy range of 1 MeV to 200 MeV that have been combined with observations from other instruments to yield spectra spanning up to four orders of magnitu de in energy. We propose to continue analyzing the archival EGRET data from gamma ray bursts, concentrating on bright bursts far outside the EGRET field of view.. The 1-200 MeV spectra will be studied for temporal trends within a burst. This study should double the number of gamma-ray bursts with measured high-energy emission.
GRO-97-057 TUELLER During a wide FOV (~100 degrees) drift scan observation on a balloon flight from Alice Springs Australia in Oct. 1995, the Gamma Ray Imaging Spectrometer (GRIS) detected (4.6 sigma) a strong source (>1 x 10-3 photons cm-2 s-1) of 511 keV g amma-ray line radiation from the Galactic plane near 280 longitude. This source has about the same intensity as the well-known Galactic center source, but it has not been previously observed. This new configuration of GRIS was designed to look for edges i n the cosmic diffuse background and provides very limited information on the position of the source. We propose an OSSE observation exactly analogous to the succcessful Galactic center mapping campaign of cycle 6 to map this bump in 511 keV emission from the plane.
GRO-97-253 VALINIA We propose to study the hard X-ray/soft gamma ray diffuse emission from the galactic plane via simultaneous RXTE/OSSE observations. The diffuse spectrum of the central region of the plane (i.e. +/-- 40 deg) in the energy interval 10 keV-10 MeV is not well understood, and the origin of the emission still remains unknown. Candidate radiation mechanisms are inverse Compton scattering, non-thermal electron bremsstrahlung, non-thermal emission from supernova remnant shells, or even thermal brem sstrahlung from hot plasma. The contribution of each component still remains uncertain. Via simultaneous observations with RXTE (fov: 1 deg FWHM), we will be able to subtract sources from OSSE's spectrum. This will allow us to: 1) simultaneously measure t he diffuse spectrum from 2 keV to 10 MeV and constrain the power law shape of the continuum spectrum, 2) set a lower limit to the latitude extension of the emission in this energy band, and 3) determine the origin of the emiss! ion.
GRO-97-010 VAN PARADIJS We propose to continue our analysis of the BATSE data base on the Bursting Pulsar GRO J1744-28. Our results so far include measurements of peak fluxes and fluences for all ~ 3000 bursts detected during the 1995/6 outburst, determination of persistent and integrated burst spectra, and a detailed analysis of the pulse phase delay during these bursts. We propose to extend these analyses to include the 1996/7 outburst. For the combined data base of ~ 5400 bursts we propose to examine burst spe ctral evolution, pulse phase spectra, and irregular variability in the bursts.
GRO-97-013 VAN PARADIJS We propose to make a joint spectral analysis of GRBs in the BATSE data base (both those triggered on board, and untriggered bursts found by a later analysis of the BATSE data base) which are located within the field of view of the SAX WFCs . The very broad-band spectral coverage obtained this way for for GRBs will allow us to test physical models of GRB spectra, improve the search for cyclotron lines by better defining the spectral continuum, and investigate the relation between the spectra l softening seen in many GRBs and their recently discovered low-energy afterglow.
GRO-97-025 VAN PARADIJS We propose to continue our search of the BATSE data base for events that did not lead to an onboard burst trigger. We have developed a complete off-line trigger search and analysis system which we have used to examine 580 days of data. We have submitted to The Astrophysical Journal a manuscript which describes our procedures and gives results from a search of 345 days of data. T
GRO-97-158 VESTRAND We propose, in collaboration with the groups operating the three leading TeV gamma-ray telescopes in the Southern Hemisphere, a campaign to simultaneously observe Cen X-3 in x-rays and MeV, GeV, and TeV gamma-rays. We request a 3-week EGRE T/COMPTEL observation of Cen X-3 during late March and early April 1998 in order to make MeV/GeV gamma-ray measurements simultaneously with scheduled TeV observations. The broad-band dataset from our campaign will constitute a unique database for modeling high-energy processes in x-ray binaries and will have an important impact on our understanding of accretion-powered pulsars. We also request access to EGRET/COMPTEL data gathered for a list of likely XRB sources that we have been monitoring since Cycle 4 .
GRO-97-206 VESTRAND We propose EGRET/COMPTEL observations as part of a campaign, in collaboration with groups operating the leading TeV gamma-ray telescopes in the Southern Hemisphere, to simultaneously observe the archetypical x-ray-selected BL Lac, PKS 2155 -304, in MeV/GeV and TeV gamma-rays. The gamma-ray observations will be supported by simultaneous satellite observations at x-ray/UV energies and by ground-based observations at radio, IR, and optical wavelengths. These measurements of PKS 2155-304, one o f the most well-studied objects in the extragalactic sky at x-ray and lower energies, will provide a key test of the ``reunification'' hypothesis for BL Lacs and, given its distance (z=0.116), uniquely probe the intergalactic infrared radiation field. We also propose new COMPTEL measurements of the prototype for ``MeV Blazars''---PKS 0208-512. The observations will allow us test for the 10-30 MeV excess we detected during Cycle 5 and to better constrain the duty cycle for outb! ursts of MeV emission.
GRO-97-093 VON MONTIGNY We propose to observe two TeV sources (Mrk~421 and Mrk~501) with the EGRET instrument for three weeks each and simultaneously with the new generation of \vCerenkov telescopes as well as with an optical telescope at Calar Alto providing opt ical polarization measurements. Both sources show a very interesting spectral and temporal behaviour in the high energy $\gamma$-ray range. From these observations we expect an improved understanding of the production mechanisms for the high energy radiat ion from BL Lac objects. The new \vCerenkov telescopes will have an energy threshold below 50 GeV and should be operational in early 1998. Therefore, we anticipate good spectral coverage with GeV/TeV instruments during Cycle 7 of the CGRO mission.
GRO-97-240 WAGNER The optical identification of gamma-ray bursts discovered by BATSE and reported by BACODINE using the Lowell Observatory Near-Earth Object Search (LONEOS) 58 cm Schmidt telescope and mosaic CCD camera is proposed. The LONEOS system images 10 square degrees of the sky to 22nd magnitude. Images will be obtained to a limiting magnitude of 22 (2-sigma) and covering 6 x 6 deg centered on the BACODINE position. Identification of optical counterparts will be based on variability, as observed prev iously in the transients of GRB 970228 and 970508, by comparison with images obtained 24-48 hours after the first images. Potential optical counterparts will be reported back through BACODINE for monitoring and measurement of their optical light curves. E xtensive ground-based facilites are available for detailed follow-up studies of LONEOS optical GRB candidates.
GRO-97-112 WASSERMAN The time histories of gamma ray emission from GRBs and SGRs will be investigated, in particular, to search for evidence of periodicities in their emission. BATSE Time-Tagged Event (TTE) data will be used in a Bayesian framework that has be en successfully applied to X-ray data.
GRO-97-065 WEIDENSPOINTNER A principal goal of COMPTEL is to study the Cosmic Diffuse Gamma Ray Background (CDG). Knowledge of the energy spectrum and the spatial inhomogeneity of the CDG may provide constraints on models that attribute the CDG to a truly diffuse or igin or to the integrated emission of unresolved point sources. The galactic north and south pole regions are of prime importance for the analysis of the inhomogeneity of the CDG because of the low galactic diffuse emission and the presence of only a few point sources. The exposure coverage of the galactic south pole region is significantly lower and far more inhomogeneous than at the galactic north pole. Four observations, with a total duration of only 8 weeks, would result in a homogeneous exposure cove rage of the galactic south pole with a depth comparable to that at the galactic north pole. This would significantly improve the analysis of the inhomogeneity of the CDG as well as of the galactic diffuse emission.
GRO-97-137 WILSON The value of actively monitoring the full sky for outbursts of accretion-powered pulsars has been considerable. During Cycles 1--6 we discovered 4 new accreting pulsars using continuously available 1.024 s data. We propose to produce and o perate a similar monitor for sources with ~64ms - 2s pulse periods, by scheduling 31 ms accumulations which favorably view the galactic plane. Sensitivities of 35 mCrab in 20 -- 50 keV can be obtained for 1/4 of the galactic plane on a daily basis. Likely objects detectable in this period range are Be-transient systems, long-period HMXRBs, GRO J1744-28 - like objects, and radio pulsars.
GRO-97-004 WINKLER We propose to analyse and interpret gamma-ray burst data using both, "single burst detector" data and "double-scatter" telescope events, from the COMPTEL instrument on board the Compton GRO. The main goal of our proposal is to continue our on-going analysis (following accepted Phase III to Cycle 6 proposals) of the constantly increasing sample of GRB's observed by COMPTEL in the MeV range. In particular, we propose to study spectral continua, investigate evidence of their time variability, analyse time histories and derive precise burst locations. Burst locations will be used to support identification of counterparts and to investigate the nature of potential repeating sources. Another important objective is to search the constantly increa sing sample of spectra for evidence of emission and/or absorption features, and high energy cut-offs. This search will be performed using data from both modes (burst detectors and telescope), combined to allow joint fits from ! 300 keV to 30 MeV.
GRO-97-118 ZHANG We propose to renew our cycle 6 proposal, to continue daily monitoring of and searching from the archival data for the hard X-ray emission from X-ray bursters using BATSE. We have discovered hard X-ray emission above 50 keV from several X- ray bursters in the previous cycles. It is now established that X-ray bursters can also produce hard X-ray emission, strikingly similar to that from black hole X-ray binaries. Studying the similarities and differences of these two classes of systems is an integral part of our investigation. We have also been carrying out correlated investigations with XTE, SAX and OSSE. Our on-going monitoring program has already triggered our TOO observations with XTE and SAX. These broad band investigations are expected to improve significantly our understanding of the nature of hard X-ray emission from these systems.
GRO-97-MIN KINZER This is a proposal to use all (or any) of the Cycle 7 Observing Opportunity viewing periods to significantly improve the rather sparse OSSE data base for measuring the OSSE detectors' scan-angle background dependences. This scan-angle background dependence is an important systematic error for OSSE non-standard observations. It can be corrected if the energy and angle dependences can be determined with sufficient accuracy. These correction factors have by now been determined to first order, but a larger data base, particularly at scan angles away from the Z axis and the X axis, are critical to accurately determining the relevant corrections for each detector. Available measurements of this scan angle dependence are clustered at scan angles around the X and Z axes because of the standard two-source observing modes of OSSE. Just a few additional measurments at angles well-separated from these axes could make a great improvement in the scan-angle dependence corrections. These scan-angle dependent background corrections are important considerations for such high-priority objectives as mapping the galactic plane, where essentially all of the observations are non-standard.