CGRO Cycle 8 Approved Program Abstracts

GRO-98-001 Mattox, John We propose to use EGRET in cycle 8 to continue to time the rotation of the Geminga pulsar. This observation is very important for the following reasons: 1. Even with EGRET's reduced sensitivity, this observation will serve to ``qualify'' t he precise ephemeris we have developed with SAS-2, COS-B, and 1991-1997 EGRET data for continuing use. 2. The EGRET timing residuals for 1991-1997 appear to have a sinusoidal modulation that is consistent with a planet of mass 1.7/sin i M_earth orbiting G eminga at a radius of 3.3 AU. The cycle 8 exposure alone cannot possibly confirm the planetary hypothesis. However, it could serve to disprove it. 3. A braking index of 17 +/- 1 is found through a coherent analysis of the 24 yr baseline provided by 1991-1 997 EGRET, COS-B, and SAS-2 observations. The cycle 8 observation together with the pending June 2-16 cycle 7 EGRET observation will help to distinguish if this is a manifestation of timing noise, or a reflection of the spin
GRO-98-003 Steinle, Helmut In this joint proposal by all CGRO inument teams, a target of opportunity observation with all four CGRO inuments is proposed to measure the spectrum of the nearest active galaxy Centaurus A in a state of ong gamma-ray emission. O bservations 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 tests of hypotheses co ncerning intensity-dependent spectral evolution which were advanced to explain the low and intermediate intensity level observations made so far with CGRO. Similar proposals have been accepted for previous cycles, but Cen A did not brighten above the high threshold set.
GRO-98-004 Iyudin, Anatoli 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 sens itivity 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 aophysically 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 few 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 o f the order of 3 $\times$ $10^{-5}$ \cms (Iyudin et al. 1995). We are confident that we could do better, 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-98-005 van Parajijs, Jan We propose to finish 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 ~5500 bursts detected during the two outbursts of the source, determi nation of persistent and integrated burst spectra, and a detailed analysis of the pulse phase delay during these bursts. We propose to finish this project with detailed studies of burst spectral evolution, and pulse phase spectroscopy and irregular variab ility within the bursts, for the whole sample of 5500 bursts.
GRO-98-008 Catanese, Michael We propose a Target of Opportunity Observation of a nearby X-ray selected BL Lac object with CGRO in coordination with the Whipple Observatory gamma-ray telescope and the Rossi X-ray Timing Explorer when the object is in a high emission st ate. Fifteen BL Lac objects, not previously detected 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 high state in the >300 GeV e mission as detected with the Whipple gamma-ray telescope, if it lasts for at least one week. This technique yielded spectacular results with Mrk 501 in 1997. By requiring an extended high state before declaring the ToO, the probability that a flare will b e detected with multiple telescopes is high. Such an observation provides an excellent test of blazar emission models. We submitted a very similar proposal in Cycle 7 that was accepted but so far has not been initiated.
GRO-98-009 Iyudin, Anatoli The discovery by COMPTEL of the $^{44}$Ti line emission at 1.16 MeV from the youngest known galactic SNR Cas A has opened a new window for the investigation of SNR properties. This discovery also shows a way that could help to uncover miss ing remnants of young galactic SNe that might have occurred some hundreds years ago and to improve our knowledge of the Galactic SN rate from the past few hundred years. Contrary to other wavelengths, in the gamma-ray band the Galaxy is almost transparent , so that otherwise obscured supernovae remnant may be detectable up to Av~10+3 in the gamma-ray line emission. The direct way to complement historical observations of the galactic SNe is to detect them by their $^{44}$Ti line emission. Finding more SNR v ia their 44Ti line emission is important not only for the global SN rate determination, but also provides an excellent diagnostic of the still poorly understood SN explosion mechanism itself.
GRO-98-013 Hurley, Kevin We propose to use BATSE data, in conjunction with data from the Ulysses and Near Earth Asteroid Rendezvous spacecraft, to localize ~1 burst every 5 days throughout Cycle 8. For those cases where only BATSE and Ulysses observe an event, the resulting error box will consist of an annulus ~5' wide by several degrees long on average. When NEAR also observes the burst, we can get ~1'x20' error boxes in the best cases. We expect ~4 bursts/month to be observed by these 3 spacecraft. We will make our results available to the wide community both by circulating them via the Global Coordinates Network, and by posting them on our web site.
GRO-98-014 Thompson, David 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 changing the software and analysis rules, we can recover a significant fraction of the lost events, allowing improved statistics for detection and study of sources. These change s can help all users obtain maximum scientific return from the EGRET data.
GRO-98-017 Bloemen, Hans We propose to complete a deep COMPTEL exposure of the Orion/Monoceros region (3 x 3 weeks). This proposal is an update of our Cycle-6 and Cycle-7 proposals, for which 8 weeks of observing time could not be scheduled. Two weeks were lost du e an AGN ToO observation and the reboost in 1997. We wish to reduce the ong asymmetry in the currently available exposure and obtain a set of observations that is less influenced by the Crab. The study of emission from the Orion/Monoceros region may be ongly influenced by this exposure asymmetry because it produces a large gradient in the inumental background in the region of interest.\ \ Recent studies show that at least part of the emission previously seen from Orion is due to inumental back ground lines. Therefore, the observations proposed here are of crucial importance now to study emission at the lower flux level.
GRO-98-019 Bertsch, Dave EGRET observed a series of four large flares in June 1991 and showed that gamma rays were emitted by the Sun to over 2 GeV and the emission persisted for over 8 hours. The observations indicate protons and electrons were produced with spec tral indices of about 3, and that continual or episodic acceleration with efficient storage was required. In view of the important new information on solar flare cosmic ray production and storage processes afforded by the early mission observations, and t he expectation that other large flares will add new insights, we propose to analyze all Phase 8 solar flares that occur in the field of view of EGRET, and to investigate all flares that are detected in the energy calorimeter. A target of opportunity is re quested under specific circumstances.
GRO-98-020 McConnell, Mark 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 of any new XRT which becomes visible during cycle 8 and which is likely to be detected by COMPTEL. We also propose to continue the analysis of archival COMPTEL data from previous XRT events, some of which show evidence for detectable emission.
GRO-98-021 McConnell, Mark We have previously generated the first all-sky map at 2.2 MeV using 5 years of data from CGRO/COMPTEL. Although generally featureless, the map does show one source (GRO J0332-87) at a significance level of ~4 sigma. One possible counterpar t is RE J0317-853, a unique DA white dwarf star with both an unusually high temperature (~50,000 K) and an unusually ong magnetic field (~340 MG). We speculate that the 2.2 MeV emission arises through some type of flaring process, although the exact me chanism remains unclear. For Cycle 7, we were awarded two weeks of observation time with both COMPTEL and OSSE that will take place in June, 1998. Meanwhile, we have been made aware of an unpublished observation of a 6 cm radio flare from RE J0317-853 tha t provides further evidence for episodic activity. We therefore propose to repeat the COMPTEL/OSSE observations of this region during cycle 8, regardless of the results from the cycle 7
GRO-98-022 Weidenspointner, Georg A principal goal of COMPTEL is to study the Cosmic Diffuse Gamma Ray Background (CDG). Knowledge of the energy spectrum and the spatial homogeneity of the CDG may provide conaints on models that attribute the CDG to a truly diffuse orig in 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 CDG because of the low galactic diffuse emission and the presence of only a few point sources. The expo sure coverage of the galactic south pole is significantly lower and far more inhomogeneous than at the galactic north pole. Three observations with a total duration of only 11 weeks would result in a homogeneous coverage of the galactic south pole with a depth comparable to that at the galactic north pole. This would significantly improve the analysis of the energy spectrum and the homogeneity of the CDG, as well as of the galactic diffuse emission.
GRO-98-023 Schoenfelder, Volker A principal objective of the COMPTEL inument is to study the large-scale Galactic emission, both diffuse and from discrete sources, and in both continuum and lines. The presence of other components is however likely, and it is a princip al goal to identify correctly the aophysical origins of the observed emission. In addition full sky mapping using the entire COMPTEL database provides a global picture of the steady discrete sources and is important for identifying potential new candia te sources. The accuracy and reliability of these analyses depend on deep and uniform exposure coverage. The combined exposure and quality of data from Cycles 1-7 is extremely non-uniform even in the Galactic plane.. We therefore propose a comprehensive s et of pointings designed to yield a more homogeneous coverage of the Galactic plane.
GRO-98-025 Sreekumar, Para The spark-chamber tracker of EGRET has traditionally been used to examine photons that arrive within 30 deg of the central pointing axis (z-axis). However, the inument is capable of detecting events incident at even larger angles. Thoug h the effective area is significantly reduced, it is not negligible. Since the raw data from EGRET retains photons beyond 30 deg, it can be used to monitor and study extremely bright sources over a much larger region of the sky. Using events with directio ns upto 50 deg from the central pointing direction, allows an increase of ~3 in the total sky coverage during the first 4.5 years of the CGRO mission when the average EGRET detection efficiency was high and the inument was configured to operate in the full FOV mode. The most exciting promise of this analysis is in the new capability to detect previously unknown large flares from gamma-ray point sources and to generate new data for duty cycle studies.
GRO-98-027 Hernanz, Margarita Detection of gamma-ray emission from classical novae, in the range between 30 and 511keV, would provide a crucial test of the thermonuclear runaway (TNR) model. This emission is a result of the annihilation of positrons, emitted by some ra dioactive nuclei (such as 13N and 18F) synthesized during the TNR; it has short duration and is produced before the optical maximum. Therefore, it can only be analyzed "a posteriori", once the nova has been discovered optically. The capability to observe all the sky, together with its high sensitivity in the low-energy range, make BATSE an ideal inument to detect this emission. In this proposal we suggest a systematic search in BATSE background data (for nearby novae that have exploded since CGRO launc h) for emission in the range 30-511keV, as well as an analysis of the new novae during the upcoming cycle. Data analysis techniques that have been applied for BATSE observation of 511keV transients of short duration will be ap
GRO-98-028 Kouveliotou, Chryssa BATSE has produced a unique data base 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 (i) to complete our study of Cug X-1 and GRO J0422+32 with the analysis of triggered and single sweep data from these sources (ii) to continue 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 future outbursts of the four transient sources over a wide range of luminosities and spectral states, and (iii) to expand this study to include new transient sources detected with BATSE in the future. Our studies cover an unprecedented t ime span of months to years.
GRO-98-029 Leising, Mark We propose CGRO/OSSE observations in Vela to confirm the COMPTEL detection of 44Ti line emission from that region, to test whether the possible SNR G266.2-1.2 is the source of that emission, and to help determine better the flux in the gam ma-ray lines. We request eight weeks of OSSE exposure to achieve these objectives.
GRO-98-030 Nemiroff, Robert 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 2500 BATSE detect GRBs through Cycle 8, there is abou t a 30% chance of finding a gravitational lens effect caused by the known galaxy field. A null detection limits the maximum average redshift of a GRB and even cosmological parameters. Previous searches provided interesting limits on models that indicate h igh GRB redshifts, and, assuming even conservative redshifts, on the cosmological constant. Lens searches may be indicating something definitive about GRBs, and useful about our universe. We propose to continue our search for a cosmological abundance of d ark matter ranging from 1E-15 to 1E12 solar masses. Previous CGRO searches led by the PI have yielded methodology and software than can be used in a Cycle 8 search.
GRO-98-031 van Paradijs, Jan We propose to make a joint spectral analysis of GRBs in the BATSE data base which are located within the fields of view of either the SAX WFCs or the ASM on RXTE. We have already developed the software necessary for the proposed analysis a nd we recently received data for two SAX and one ASM burst. The very broad-band spectral coverage obtained this way will allow us to test physical models of GRB spectra, determine the number and energy diibution of spectral breaks, improve the search f or cyclotron lines by better defining the spectral continuum, test whether X-ray tails are a seperate emission component or result from spectral evolution of the main component, and investigate the relation between the spectral softening seen in many GRBs and their recently discovered low-energy afterglow.
GRO-98-032 The, Lih, Sin The COMPTEL detection of Ti44 1.157 MeV line flux of (4.8+-0.9)e-5 ph/cm**2/s in the Cas A SNR is an exciting discovery of CGRO. Gamma ray observations of Cas A provide the unique opportunity to measure the synthesis and ejection of a spec ific isotopes from the innermost part of a single supernova. However, the situation regarding the line flux and therefore the Ti44 mass synthesized appear to be unsatisfactory with OSSE and HEXTE have not been able to confirm the COMPTEL's detection. We p ropose a twelve week OSSE 4-detector Cas A observation to obtain at least 3sigma detection of Ti44 decays with a flux of 4.2e-5 ph/cm**2/s in the 68 & 78 keV and 1.16 MeV lines. We will combine all OSSE data with Cas A data from HEXTE measurements expecti ng at the end a 1sigma uncertainty in the flux of ~9e-6 ph/cm**2/s or ~5e-5 Msun in the mass of Ti44.
GRO-98-034 Steinle, Helmut We propose to monitor the Sun approaching the solar maximum during two long duration observations, each lasting 6 weeks. We limit our data request to the solar data (from COMPTEL, EGRET OSSE) that are needed to analyze the gamma-ray and ne utron emission of up to three solar flares, which occur during each of those observation periods, leaving a wealth of solar data to other proposers. The pointing of CGRO during those two observations will be such, that two regions on the sky will be obser ved which have so far not been observed with dedicated pointings, thus completing the COMPTEL all-sky-survey. COMPTEL will observe the two regions continuously, whereas the EGRET spark chamber will be switched on only if major flares occur and OSSE will b e moved to view the Sun in such cases. By combining solar observations and the completion of the COMPTEL sky-survey, the best use of CGRO time is made during these long observations.
GRO-98-039 Diehl , Roland COMPTEL 1.809 MeV measurements have shown an image of 26Al source regions along the plane of the Galaxy, where the inner Galaxy clearly dominates the all-sky 26Al emission. But more interesting new features have been discovered, in particu lar substantial emission from regions not in the inner Galaxy. The inner Galaxy and bulge may not dominate the Galactic 26Al production as much as expected initially. Localized source regions more nearby may provide an important clue to contributions from secondary sources. COMPTEL's images show promising features in the anticenter region at low significance and intensity, which are typically indicative of extended emission. Those may be nearby emission regions associated with the prominent molecular clou ds of Cepheus, Perseus, and Taurus. We propose to improve exposure in this region far away from the confused inner-Galaxy region, and hence more plausibly identified with source regions of rather
GRO-98-044 Collmar, Werner The detection of gamma-ray emission from blazars by the CGRO experiments has provided new and important insights in the emission processes of blazars in general. It is believed that in blazars the non-thermal continuum from X-ray to gamma- ray energies is due to Comptonisation of soft photons by relativistic jet electrons. However many questions remain unanswered, e.g. the nature of the soft photons, time correlations between different high-energy wavebands. We propose simultaneous gamma-ra y and X-ray observations of selected, time-variable gamma-ray blazars (3C 273, 3C 279, PKS 0528+134) to simultaneously determine their high-energy properties. Especially to investigate the relationship between soft X-rays, hard X-rays and gamma-rays by co mparing measurement covering different X- and gamma states. Such multifrequency observations should be carried out as long as functional gamma-ray detectors are still in operation.
GRO-98-045 Diehl, Roland The COMPTEL 1.809 MeV measurements have shown substantial emission from regions far away from the inner Galaxy, the Vela and Cygnus regions: Here a unique calibration of nucleosynthesis models for the candidate source types appears possibl e, since the morphology and the object populations in those regions are known to much better precision than in the inner Galaxy. In particular, a limit on 60Fe emission could conain SNII versus WR stars. For Cycle-7, a largely identical proposal was ac cepted, yet only 14 out of the requested 56 days of observation were scheduled. We propose to perform dedicated observations of the Cygnus region. We expect to separately identify emission from the Cygnus superbubble, and foreground WR stars, and be able to assess the Cygnus region nucleosynthesis history from 26Al conaints as combined with other recent observations of the region, e.g., in CO and X rays.
GRO-98-046 Grove, Eric We propose broadband TOO observations of the black hole candidate GX339-4 in the X-ray high/soft state. High-sensitivity gamma-ray observations of this source have never been made in this spectral state. The broadband spectral studies will determine physical processes in the source, which we will contrast with our recent studies of simultaneous Ginga/OSSE observations of GX339-4 and Cyg X-1 in the X-ray low/hard state. OSSE observations alone will measure or set a lower limit on the break energy of the gamma-ray power law expected in the high/soft state.
GRO-98-047 McConnell, Mark We have recently generated the first consistent broad-band spectrum of Cyg X-1 using contemporaneous data from COMPTEL, BATSE and OSSE, thus providing a valuable cross-calibration of these three experiments. This gives us the confidence to proceed with generating additional broad-band CGRO spectra. Of particular interest is the nature of the spectrum near 1 MeV, for which COMPTEL data is most useful. In producing broad-band spectra, the COMPTEL statistics can be increased considerably by r elaxing the requirement for contemporaneous OSSE data and using only COMPTEL and BATSE data. For this purpose, we can use BATSE spectra generated with both standard occultation analysis and with the JPL-EBOP analysis. We propose to generate such broad-ban d spectra for various spectral states of Cyg X-1. These data would provide useful input to theoretical models for the broad-band emission and perhaps offer some insight as to the nature of the
GRO-98-048 Grove, Eric We propose target of opportunity OSSE observations of bright (exceeding half Crab) transient emission from X-ray pulsars. Through phase-averaged and phase-resolved spectroscopy, we will address the following issues. (1) Search for complex spectral 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 d ecay portion of an outburst. This is a resubmission of an expired GRO Cycle 4-6 multiyear and Cycle 7 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-98-052 van Paradijs, Jan We propose to continue our search of the BATSE data base for gamma ray bursts (GRBs) and other transients that did not lead to an onboard burst trigger. We have developed a complete search and analysis system which we have used to examine 2200 days of data. The resulting preliminary catalog of untriggered events contains 906 GRB candidates, 13 likely bursts from SGR 1806-20 and/or SGR 1814-13, 2405 solar flares, and 318 low-energy (25--50 keV) events of unknown origin. Our off-line search is sensitive to GRBs with peak fluxes lower by a factor of 2 than can be detected with the onboard burst trigger in its usual (5.5 sigma, 50--300 keV) configuration. This research will increase the number of GRBs detected with BATSE by 40--50 percent and it will provide a catalog of transients of unknown origin. The catalogs we produce will be made available to the public via the World Wide Web.
GRO-98-054 Thompson, David We propose to continue analyzing both archival and new gamma-ray burst spectra using the EGRET NaI (TASC) detector, sensitive in the range 1 to 200 MeV. Because the TASC is omnidirectional, bursts can be detected far beyond the nominal EGR ET field of view; preliminary analysis indicates that the wide-angle analysis doubles the number of bursts that EGRET can detect at high energies. The 1-200 MeV spectra will be studied for temporal trends within a burst and will be combined with data from other inuments to produce broad-band spectra.
GRO-98-055 Hartman, Robert To improve understanding of physical processes in blazar jets, which can produce large observed luminosities of gamma rays, we propose Targets of Opportunity (ToO's) to observe gamma-ray emission correlated with exceptionally bright emissi on in lower frequency bands. The objective of this work is to determine the time delay of correlations between short-term (~day) variations in different bands, and thus to limit possible emission mechanisms. The objects selected for consideration either h ave demonated previous bright high-energy gamma ray flares, or are EGRET-detected and well-monitored at lower frequencies. A ToO trigger could arise from an exceptionally bright and rising state in either the optical or submm band. In addition, we prop ose 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. In that case, we propose to share the ToO extension data with the PI for the sche
GRO-98-056 Strickman, Mark 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. For CGRO Cycle 7, we proposed to study the behavior of this tail in more detail with a longer OSSE observation, performed in conjunction with a multiwavelength campaign. Although highly rated, scheduling difficulties prevented implementation of this program. Hence, we are reproposing our plan to l earn more about the morphology of hard X-ray variability from Sco X-1 and how it correlates to behavior in 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 l ow-mass X-ray binaries.
GRO-98-057 Meegan, Charles Population studies of gamma-ray bursts are sensitive to trigger biases in the BATSE burst catalog. Conflicting conclusions about these biases have been published. We propose to perform a more complete study of trigger biases arising from i numental effects, including the effects of triggering on statistical fluctuations (the peak counts bias) and the bias against "slow risers". We will examine Malmquist biases to clarify the assumptions on which they are based. The goal of the proposal i s to provide more accurate efficiency corrections and to enable users of BATSE data to understand how the various biases may affect their analyses.
GRO-98-060 Wilson, Colleen We propose to do a pulse timing study of the long period accretion powered X-ray pulsars 4U 1145--619 and A1118-619. We will develop an algorithm which will improve the sensitivity for long period pulsars of the existing pulsed monitor by reducing systematic effects produced by Earth occultations of bright sources and bright Vela X-1 pulses. With this improved sensitivity we will search for previously undetected outbursts from both sources and analyze known outbursts. We will generate puls e profiles and histories of pulse phase, frequency, and intensity. We will search for pulse shape changes during outbursts for both sources and among outbursts for 4U 1145--619. For both systems, we will attempt an orbital analysis and search for correlat ions between torque and intensity.
GRO-98-061 Dingus, Brenda We request the equivalent of approximately one week of EGRET viewing time to study the highest energy emission from gamma-ray bursts. EGRET will turn on the spark chamber tracking detector for 10,000 seconds upon receipt of a BATSE generat ed trigger of a bright burst within 40 degrees of the EGRET axis. This mode of operation has been used since Cycle 5 with a current average rate of one BATSE trigger every 17 days. All recent COMPTEL burst detections have been observed by EGRET with this trigger. For all bursts with spectra determined by COMPTEL, EGRET fluxes and upper limits show no evidence of any high energy cut off. The average spectrum measured by EGRET is as hard as measured by COMPTEL. Improved spectra and temporal evolution studie s are planned with archival analysis of EGRET spark chamber events which do not pass gamma-ray cuts but are clearly associated with bursts.
GRO-98-067 Kippen, R. Marc The ability to localize gamma-ray bursts is one of BATSE's greatest engths. Unfortunately, BATSE locations currently lack the precision needed for counterpart searches and investigations of small-angle properties. A significant part of this imprecision is due to the fact that the localizations are approximated by circular "error boxes." We propose to study and implement an improved characterization that would more closely preserve the true asymmetrical nature of BATSE burst localization s, thereby reducing systematic errors. The improved characterization will be provided for all past and future BATSE GRBs, and will be incorporated into the BATSE Rapid Burst Response system for use in rapid counterpart search efforts. A particularly impor tant aspect of our investigation is that it will improve the locations of weak bursts. BATSE is currently the only inument capable of studying such events.
GRO-98-073 Ulmer, Mel Pulsars are highly magnetized, rotating neutron stars, and although they were discovered over 25 years ago, we still do not understand how pulsars shine and why some pulsars are bright gamma-ray sources. This proposal this to continue the search for hard X-ray/gamma ray emission from isolated known radio pulsars. This proposal is to apply this search to archival data only. These results will be used to derive models for the gamma-ray emission from isolated pulsars. The models will include the dependence of the radio pulsar beaming direction toward the earth derived from polarization measurements. We will also delimit the beam width and beam intensity by using the the statistics of how many pulsars are detectable versus how many were observ ed.
GRO-98-078 Paciesas, William We propose to continue our Cycle 7 project to produce and maintain a comprehensive set of catalogs of BATSE gamma-ray burst spectra that will be of general use to the aophysical community. The catalogs will make use of the wide range of BATSE data types and allow convenient access to deconvolved spectra and corresponding standard model functional fit parameters with various combinations of time and energy resolution. The catalogs will be delivered to the CGROSSC for dissemination, and w ill be updated regularly as new burst data come in.
GRO-98-079 Brainerd, Jerome We propose a continuation of the study of whether the BATSE gamma-ray burst E-peak diibution is a consequence of inumental effects, and whether the true diibution of E-peak has a characteristic value of approximately 200 keV. In r esearch conducted under CGRO Cycle 7 funding, we derived the BATSE burst trigger efficiency as a function of E-peak for different trigger energy ranges. Under the current proposal, we will determine the systematic error in deriving E-peak, examine the eff iciency of BATSE to detect soft sources such as SGRs and hard sources such as TGFs, compare the burst characteristics derived by BATSE to those derived by Comptel, and compare model diibutions of E-peak with the observations to place limits on the intr insic E-peak diibution.
GRO-98-081 Pendleton, Geoffrey We consider several distinct models for the production of gamma-ray bursts at cosmological distances. All of these models are capable of producing spectra with significant high-energy emission, as well as spectra where the high energy emis sion is suppressed. However, these models predict distinctly different correlations between several spectral observables during periods of rapid high-energy spectral evolution. We propose to identify a population of emission peaks in GRBs that exhibit spe ctral transitions from significant emission above 300 KeV to a marked lack of high energy flux. We will then perform spectral fits to contiguous intervals spanning the emission peaks to quantify the evolution of spectral parameters across the peaks. The r esulting ensemble of high-energy spectral evolution data will be compared to the model predictions to see which is preferred by the data.
GRO-98-085 Kanbach, Gottfried We propose to observe PKS 0208-512 for 3 weeks with EGRET, COMPTEL and OSSE. PKS 0208-512, a bright, isolated high-energy blazar, was observed previously only twice in the central field of view. It shows ong variability, the high-energy spectra are hard and show evidence of shape variations with intensity up to a spectral break at 4 GeV. COMPTEL detected PKS 0208-512 with a ong spectral excess at 1-3 MeV in several epochs ('MeV-blazar'). OSSE has not yet observed the source. Measurem ents at a new epoch will shed light on two competing models which try to explain the multi-component spectra: (1) a blue shifted, broadened annihilation line from a relativistic pair plasma superimposed on a Compton continuum, or (2) multiple Comptonisati on components from differently energized particles. Both models lead to distinct predictions for the spectral components' shape, variation, and correlation.
GRO-98-088 Mukherjee, Resmi The proposal requests EGRET and COMPTEL data rights for the blazar PKS 0528+134 if an observation of the galactic anticenter region is made by EGRET. Such an observation may be scheduled for EGRET calibration purposes. We propose to monito r PKS 0528+134 to check for gamma-ray flares. If PKS 0528+134 is found to be flaring, we propose to request a target of opportunity extending the EGRET observation by a week. In the event of a gamma-ray flare in PKS 0528+134, the observations may provide us with the last opportunity to study short time scale flux variations correlated with observations at longer wavelengths.
GRO-98-091 Preece, Robert This project will examine the detailed behavior of the gamma-ray burst low-energy continuum, by analyzing a large sample of bright archival and Cycle 8 events, using joint spectral fits between the BATSE Spectroscopy Detector discriminator and LAD high energy resolution data. We wish to determine if there exists a separate class of `low energy' bursts in the population of low E_peak events, as suggested in observations by Ginga. With the improved statistics available in this study, these m ay be found to be merely an extension to the already well-determined log-normal diibution of E_peak. Another outcome will be to determine the existence of an additional continuum feature in the form of a second, low-energy break. At the same time, we e xpect to complete the Cycle 7 project investigating the time-resolved spectroscopy of the X-ray excess that was previously found in 15% of all bursts.
GRO-98-094 Finger, Mark We propose a systematic study of accreting pulsars using BATSE. The full sky will be monitored daily for pulsars with spin frequencies between 2 mHz and 0.5 Hz. Her X-1 will be monitored during Main High states. Quick-look estimates of the flux and frequencies of all detectable pulsars will be provided on the world-wide web, and refined measurements will be provided in updates to the long-term pulsar histories and databases currently available through the Compton Observatory science suppor t center. We propose in-depth studies of transient pulsars, Her X-1, Cen X-3, OAO 1657-415, and Vela X-1.
GRO-98-096 Zhang, Shuang We propose to conduct a comprehensive multiwavelength campaign of the peculiar candidate black hole binary system GX339-4, which has displayed four spectral states (off, low, high and very high), and is capable of producing multiple hard X -ray outbursts with relatively short intervals. An unusual optical/X-ray anti-correlation was also observed from it, similar to that seen in the superluminal jet source GROJ1655-40. Recently a radio jet-like feature was also seen from it. It is thus an id eal laboratory for studying these important aophysical issues: transient source outbursts, hard X-ray production, spectral state transitions, and radio emission, including jet formation. The proposed observations consist of: a) long term radio, optical , X-ray and hard X-ray monitoring; and b) TOO observations of OSSE (gamma-ray), ATCA and VLBI (radio).
GRO-98-097 Connors, Alanna We propose to maintain and continue to upgrade the ongoing Rapid Burst Response (RBR) program of COMPTEL, CGRO's MeV-range imaging telescope and transient spectrometer. We provide 1-2 degree localizations (as well as MeV light-curves) with in a few to 45 minutes after burst onset for one burst every few months. These act as triggers for prompt repointing of other high energy satellites, in concert with BATSE-RBR and sometimes RXTE/ASM or IPN positions; as well as for ground-based observatio ns. Theories of gamma-ray burst and afterglow emission are still poorly conained. Near real-time multi-wavelength observations can help distinguish which physical mechanisms are key. We emphasize that these are possible, with the help of these RBR syst ems. Not only at high energies, but optical/IR - from the burst itself or directly after, not the delayed afterglow tail - may be detectable ~minutes after burst onset by systems either on-line now or soon during the
GRO-98-101 Harmon, B. Alan The Earth Occultation Team (EOT) at Marshall Space Flight Center routinely performs all-sky monitoring and detection tasks for the Burst and Transient Source Experiment (BATSE). The current effort includes monitoring $\sim$100 ong hard X-ray/low energy gamma ray sources in the 20 keV$-$2 MeV energy range with the Large Area Detectors, and occasional detection and characterization of new or unusual transient behavior. Beyond the quick-science analysis activities of the EOT, we propose to enhance several aspects of this work during Cycle 8: (1) Continue production of a source catalog paper, (2) continue expansion of Web access to Earth occultation monitoring information, (3) refine the galactic plane imaging technique, and (4) initiate ge neral improvements to the monitoring capability.
GRO-98-102 Fishman, Gerald We propose to continue an approved Cycle 7 Guest Investigation to re-point CGRO as a Target of Opportunity (ToO) in response to ong gamma-ray bursts. The Cycle 7 ToO has not yet been carried out. Even though the proposal was rated outst anding (4.65), only one observation was approved, out of four requested. In the past year six additional x-ray afterglows have been detected from gamma-ray bursts. In addition, there have been theoretical models published (cf. Bottcher; Vietri) that predi ct high-energy, delayed gamma-ray burst emission from proton synchrotron radiation and pion decay. In one model, the flux estimates are within an order of magnitude of the EGRET sensitivity. In view of the large model uncertainty and EGRET's detections of delayed emission from at least two GRBs, the prospects are moderate for a positive ToO observation. Thus, we believe that there is new justification to continue this investigation with three additional ToOs.
GRO-98-103 Perlmutter, Saul BATSE has the potential to provide an order of magnitude more OTs than are currently being discovered with the BeppoSax satellite. With such a large sample of OTs, the diibution of properties would challenge current models, and the brig hter and longer OTs would likely permit breakthroughs with low-noise spectra, detailed host studies, polarimetry, etc. BATSE/GCN alerts also permit the study of optical emission on time scales approaching that of GRBs. We will tap these potentials with ou r 5deg field telescope & CCD, which already respond automatically to GRBs. Our automation for nightly operation is nearly complete, and our sensitivity to previous OTs is already demonated. We expect to provide 20-41 images of GRB positions, yielding ~ 5-10 OT discoveries/year. More than 5 positions will be imaged/year within 20 sec of gamma emission with V>17.7 mag sensitivity in 10 sec. Continued GRO support will yield discoveries starting Sept.-Dec. 98.
GRO-98-104 Stacy, J. Gregory Data-analysis software tools have been developed by the CGRO/COMPTEL inument team to produce all-sky maximum-likelihood maps using data acquired over the entire CGRO mission. We propose to exploit this new capability to produce a more complete set of COMPTEL maximum-likelihood all-sky maps, using improved inument-response functions and refined event-selection criteria. With these all-sky maps we intend to extend our ongoing study of the properties of active galaxies and other known a nd candidate gamma-ray sources lying at high Galactic latitudes. Our scientific objective is to derive the global properties of such gamma-ray sources in the medium-energy gamma-ray regime, and to provide cumulative fluxes or limits in the COMPTEL energy range for all high-latitude sources of general interest. These time-averaged results will also be compared with source studies for individual CGRO viewing periods carried out by us
GRO-98-105 Zhang, Shuang We propose to renew our cycle 7 proposal to continue daily monitoring and search archival data for hard X-ray emission from X-ray bursters using BATSE. For cycle 8, we also propose to include all X-ray bursters discovered with the SAX/WFC. We have discovered hard X-ray emission above 50 keV from several X-ray bursters in previous cycles. It is now established that X-ray bursters can also produce hard X-ray emission that is ikingly 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 obse rvations 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-98-107 Tavani, Marco We iterate for Cycle 8 our approved program for TOO observations of new gamma-ray transients in the Galactic plane approved for Cycle 7. We propose to study new gamma-ray transients (GRTs) with no radio-loud blazar-like counterparts locali zed 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, OSSE, COMPTEL and BATSE data rights for all GRTs of gamma-ray flux above 1xE(-6) ph./cm**2/s within +/- 30 degrees of Galactic latitude, and exclusive data rights for the first GRT detected during Cycle 8. EGRET quicklook analysis will be used to trigger rapid follow-up multiwavelength studies. We will request a GRO TOO observ ation in case EGRET detects a new GRT of flux above 2 x E(-6) ph./cm**2/s.
GRO-98-108 McConnell, Mark We propose to analyse and interpret gamma-ray burst (GRB) data using both the telescope mode data and the single detector burst mode data from COMPTEL. Collectively, these data span the energy range from 300 keV up to 30 MeV. The first goa l of our proposal will be to perform a standard analysis for each significant GRB event seen by COMPTEL. This includes GRBs that are registered by the telescope mode data as well as GRBs that are registered only in the burst mode data. We would also defin e a set of standard data products (including deconvolved photon spectra) that, for each detected GRB event, would be made available via the COMPTEL GRB Web Page. The second goal of our proposed program will be to perform more detailed studies of selected GRB events. This would represent a continuation of past GRB studies by the COMPTEL team.
GRO-98-112 McCollough, Michael We propose a target of opportunity observation (ToO) of a major flare of the relativistic jet source Cyg X-3. We will obtain data from BATSE, OSSE, and COMPTEL throughout the observation. This will give us coverage from the hard X-ray to t he soft gamma-ray for the entire ToO. In addition, during the radio flare we will obtain hard gamma-ray measurements from EGRET. These observations will be triggered based on hard X-ray and radio monitoring observations.
GRO-98-116 Kouveliotou, Chryssa During the first 7 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 third reactivation of the latter source initiated a TOO with RXTE, which resulted in the first unambiguous detection of a ongly magnetized (B>1E14 G) pulsar associated with an SGR, which ongly supports the magnetar model for SGRs. We propose to continue our succesful SGR project by: (i) a search for evidence for Global Seismic Oscillations following SGR bursts in the BATSE data, and (ii) combining the spectral data from BATSE and the RXTE/PCA to make a detailed time-dependent spectral analysis of SGR events.
GRO-98-118 Barthelmy, Scott We propose (1) to continue to operate the BATSE Coordinates Diibution Network (BACODINE), (2) to improve the GRB location accuracy & (3) aggressively pursue new customers & modify the operation to meet the customer's needs. BACODINE (no w part of GCN) is a system that calculates GRB locations from the BATSE telemetry data in real time & diibutes those positions to inuments to make multi-band follow-up observations of GRBs in real time (less than 6 seconds) while the GRBs are still bursting. The SAX observations have shown that near-realtime follow-up observations are critical to counterpart identification. The growing & improving ensemble of BACODINE site inuments are setting ever more ingent upper limits at ever shorter time delays. BACODINE facilitates observations in the time domain shorter than are possible with the SAX locations. Continued operations will improve these limits & allow for more counterpart identifications.
GRO-98-120 Mitrofanov, Igor The concept of emission time tau50 is suggested, as a complementary temporal parameter to the classical parameter of duration T50. It is defined as time of emission of 50\% level. We perform the test of the bimodality of bursts using tau50 and study the diibutions of tau50 and duty cycle tau50/T50 for different intensity groups of bursts. Parameters tau50*, Ep* are also implemented for each burst, as emission time measured at spectral peak energy and peak energy measured along correspon ding emission time. Using these parameters and the product (tau50* x Ep*), as the cosmological invariant, we test effects of hardness/duration/intensity correlation. The hypothesis is checked that emitters have standard diibutions at different red-shif ts. The luminosity dependent properties are studied in comoving frames. The evolutionary effects of emitters at different red-shifts are also investigated.
GRO-98-124 Briggs, Michael Current cosmological models for the origin of gamma-ray bursts place even the brightest bursts at redshifts affected by spatial curvature. Consequently, cosmological signatures such as spectral redshifting should be apparent even among the brightest bursts, the bursts which fall on the brightness diibution's -3/2 power law component. Under the revised cosmological interpretation, the -3/2 power law is not due to a homogeneous diibution of sources, but rather to a balence between an e volving source density and cosmological spatial curvature. We propose to use BATSE data to determine whether the hardness-intensity trend observed between the brightest and dimmest bursts continues among the brightest bursts.
GRO-98-127 Dixon, David Recent work has indicated that the diibution of Al26 is perhaps not as clumpy as shown in Maximum Entropy maps of COMPTEL 1.8 MeV data (Kn\"odlseder 1997). We propose to continue this study, using wavelet techniques to make improved map s and statistically quantify the smoothness of the Al26 diibution as seen by COMPTEL.
GRO-98-128 Matz, Steven By using a rapid slewing response system to promptly (10--100s after trigger) observe burst positions calculated on-board GRO by BATSE, the OSSE inument has discovered persistent gamma-ray burst emission >100 keV with power-law decays. These detections demonate OSSE's unique capability to extend the study of burst afterglows to the primary energy range of the burst itself, and to times near to the trigger. We propose to continue the operation of the rapid response system and analysis of these slew observations (1--2 events per month) as well as any serendipitous burst detections (0.5--1 events per month). These observations, combined with data at other wavelengths, will form a more comprehensive picture of the afterglow phenomenon, a nd conain current models of burst and afterglow production.
GRO-98-130 Liang, Edison The discovery of a new SGR 1814-13 and the announcement of periodicities in SGR 1806-20 and SGR 1900+14 has focused attention on these highly unusual sources. In Cycles 4-7 we have been performing spectral fitting and theoretical studies o f the SGR bursts seen by BATSE, and multiwavelength observations and modeling of the highly unusual quiescent counterparts from the millimeter through the infrared. We propose to continue both these projects in Cycle 8. We request non-exclusive data right s to the BATSE data from any new bursts in Cycle 8.
GRO-98-131 Liang, Edison This is a Compton cycle 8 Guest Investigator Proposal for the renewal of cycle 7 grant NAG 5-3840. It concerns the analysis and modeling of gamma-ray burst (GRB) continuum spectral evolution data obtained by BATSE. This project is an on-go ing collaboration between Rice University and the BATSE inument teams. Following the major developments of this past year, we will focus in cycle 8 on GRB spectral evolution properties that bear most on the multiwavelength (radio-X-rays) behavior of GR Bs and their afterglows, and potential conaints on the different cosmological scenarios. This is the core research project of our group at Rice.
GRO-98-132 Matz, Stephen With its high sensitivity and large but well defined field-of-view, OSSE is the only operating satellite inument with the capability of mapping the detailed diibution of diffuse galactic positron annihilation radiation and continuum emission 0.05--1 MeV. Mapping techniques developed under previous proposals can achieve resolutions of up to ~1--2 degrees using OSSE data. These techniques, applied to data from OSSE, SMM, and TGRS, have led to the discovery of an unexpected asymmetry in the galactic latitude diibution of the 511 keV annihilation line. This proposal, which is a continuation of an approved Cycle 7 proposal, requests a sequence of observations which will be used to 1) complete the mapping of the diffuse galactic emissio n over the longitude range ~10--55 and 2) extend the uniform mapping data to the other side of the disk, -55 < l < -10. These observations will provide improved sensitivity to diffuse emission over all previous and currently p
GRO-98-133 Connaughton, Valerie Observations of X-ray, optical and radio counterparts to gamma-ray bursts hours to days after the initial GRB event have helped confirm the cosmological origin of the bursters. Recent afterglow measurements have concentrated on emission wh ich is softer than that seen during the prompt GRB. The most spectacular delayed emission prior to GRB 970228, however, came from the EGRET detection of photons 5400 seconds after BATSE GRB 940217, including one photon of energy 18 GeV. Following the EGRE T result, and suggestions that shocks from GRBs may be sites for cosmic ray acceleration, we propose here to explore afterglow emission at energies of hundreds of GeV with the Whipple Observatory. We plan to perform observations of 3 well-localized GRBs w ith coverage of several hours over a period of at least 2 days each. We hope to involve other ground-based high-energy experiments to provide a continuous time-line for the observations.
GRO-98-134 Connoughton, Valerie We propose to continue our hard X-ray survey of 87 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 deection 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- se lected BL Lac objects in an effort to examine hard X-ray differences, if any, between two classes. We propose also to investigate a recent claim that X-ray selected BL Lacs fall into two categories, one of which should only be seen in hard X-rays as a fla ring source. Recent analysis has shown that BATSE can detect flares from these sources on time-scales of days, so that an examination of the variability of our X-ray selected sample should be a good test of this theory.
GRO-98-137 Phlips, Bernard We propose an observation of the black hole candidate Cygnus X-1 with OSSE and COMPTEL. Many such observations have already been made, but more time is needed if one is to accurately determine the high energy spectrum between 0.5 and 2 MeV . The detailed shape of the fall off of the spectrum near 1 MeV might be one of the few measurements available to discriminate between the various classes of black hole models currently in favor. The models are currently not very conained at high energ ies because of the limited statistics available of simultaneous times with OSSE and COMPTEL. Since the INTEGRAL continuum sensitivity near 1 MeV will be similar to OSSE and COMPTEL, a deep observation of Cygnus X-1 really should be performed in the out ye ars of the CGRO program.
GRO-98-138 Phlips, Bernard 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 ASM on RXTE. We consider t his to be the definition of the state of Cygnus X-1 when enhanced MeV emission was detected during the HEAO-3 mission. Until RXTE, there was no way to differentiate between the source going in the known X-ray high, gamma ray low state, and a potential rar e state of X-ray low, gamma ray low emission. The observation would be contemporaneous with an RXTE ToO and possibly USA observations. The primary goal of this proposal is to confirm the existence of the MeV emission if the source goes in the defined stat e. 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. This is a resubmission of an approved cycle 7 proposal.
GRO-98-139 Kuiper, Lucien Surprisingly, recent improved COMPTEL timing studies of PSR B1509-58 using a combination of Cycle 1 to 6 observations shows that pulsed emission is detected up to at least 10 MeV. Above 10 MeV a significant source consistent in position wi th the pulsar is detected in spatial analysis. Timing analysis in the 10-30 MeV energy range, however, yielded a modulation significance of only $\sim 2\sigma$ with indications for a new pulse (near phase 0.85) in a phase region showing no ucture at lo wer energies. Timing analysis in the adjacent 30-100 MeV EGRET energy range shows similar indications. Here we propose to observe PSR B1509-58 with COMPTEL for a total duration of 6 weeks. In combination with the analysed Cycle 1-6 and unanalysed Cycle 7 data this should be sufficient to clarify the emission properties of PSR B1509-58 above 10 MeV.
GRO-98-140 Vestrand, W. Thomas We propose to continue our successful search for sporadic gamma-ray emission from X-Ray Binary Systems (XRBs). Our preliminary analysis of COMPTEL data suggests that GX 339-04 is a source of MeV emission during hard x-ray outbursts. To con firm the potential detections, we propose refined analysis of archival COMPTEL data as well as a ToO campaign of joint OSSE/COMPTEL and RXTE observations that would be triggered by a BATSE detection of an intense hard x-ray outburst. We request a short, one-week, EGRET observation of Cygnus X-3 to test further the controversial claims for variable GeV emission from the system. We also request access to any additional EGRET/COMPTEL data gathered for a list of likely XRB sources that we have been monitoring since Cycle 4.
GRO-98-141 Johnson, W. Neil To date, the most accurate spectra yielding the most useful physical information about the radiative processes in Seyfert galaxies are provided by multiwavelength, multi-satellite simultaneous observations. The launch of AXAF will provide us with greatly improved X-ray data, but a meaningful interpretation of these data will be greatly enhanced by extending the observations to the highest possible energies. To that end, we propose multiwavelength X-ray/gamma-ray campaigns involving the CGR O OSSE and RXTE, to be conducted simultaneously with AXAF. Our targets, IC 4329A, NGC 4388, and NGC 4945 (all in the GTO programs or proposed by us in the AXAF GO program) are archetypical gamma-ray-bright Seyferts of type 1 - 2; and NGC 4151 is the brigh test radio-quiet Seyfert (type 1.5). The resulting X-ray/gamma-ray spectra will test the unified models of AGN, and will allow us to study the physical processes responsible for the emission.
GRO-98-143 Ryan, James We propose to conduct CGRO-wide ToO observations of the Sun as we approach solar maximum, requesting up to two such ToOs during Cycle 8. Each ToO would be triggered by NOAA solar activity forecasts. The only other CGRO solar ToO (June 1991 ) yeilded many important new discoveries and we can expect additional insights from any future ToO observations. The focus of this proposal is first to obtain data from large X-class gamma-ray emitting flares, but also to acquire data from smaller events that would also occur during these observations. We request all solar-related data for COMPTEL, OSSE and BATSE from these observations. These data would be jointly analyzed with those from EGRET obtained through a separate, but similar, ToO proposal. The inument operating modes would be optimized (based on past experience) for solar flare measurements. Despite GI data rights, data and results would be made available to other users as soon as possible via the World
GRO-98-144 Kazanas, Demos We propose a combined spectral-temporal analysis of the black hole candidates Cyg X-1 and GX 339-4 as well as a possible future X-ray transient with particular emphasis in the Fourier ucture of the lags between different energy bands. W e have argued that such an analysis can provide, in addition to the Thomson depth and the electron temperature of the hot corona, also its size and radial density ucture. Earlier observations by Ginga and RXTE have hinted for different density uctur es at different epochs (timing states). Our goal is to confirm these results and search for correlation between these timing states and the well known spectral states of these sources in the OSSE energy band too.
GRO-98-145 Dermer, Charles We propose to search for nuclear and starburst activity in the nearby infrared luminous merger NGC 6240 using gamma-ray observations with the OSSE inument. This source is an example of a class of ultra-luminous (> 10^11 L_Sun) far-infra red galaxies (ULIGs) that emit the bulk of their radiation at far-infrared wavelengths. ULIGs are among the most luminous objects in the universe, and provide important clues to the process of galaxy formation and the origin of nuclear activity in galaxie s. Because ULIGs are obscured by gas and dust, the detection of buried active nuclei from some of these systems may only be possible with gamma-ray detectors. Recent ASCA observations show variable X-ray activity in NGC 6240; thus its nuclear origin could be confirmed with OSSE observations.
GRO-98-148 Kroeger, Richard We propose Target of Opportunity observations with OSSE of bright transient sources believed to be black hole candidates. Previous observations of such transients with OSSE have resulted in the elucidation of two gamma-ray spectral states of BHC emission that correspond to X-ray spectral states (Grove et al. 1997, 1998). Long TOO observations increase the likelihood of observing spectral state transitions, which are known to have occurred in at least four BHCs.
GRO-98-149 Kurfess, James Purcell et al. (1997) recently reported an asymmetry in the galactic latitude diibution of the 511 keV annihilation line showing an enhancement extending to ~7-10 deg. above the galactic center region. During CGRO cycle 7, OSSE observat ions were undertaken of the "Fountain" region to better determine the location, diibution, morphology and flux of the positive latitude enhancement. Preliminary results from the cycle 7 observations exhibit the same high latitude excess. It is not yet clear whether or not this this feature is directly associated with activity in the galactic center region, although similar latitude asymmetries are seen in radio maps of the GC region. OSSE is the only operating satellite inument capable of studying t he detailed diibution of this radiation. We propose cycle 8 observations observations to extend the coverage of the GC region to negative latitudes, to determine the extent of the asymmetry and to help clarify the origin of
GRO-98-150 Hunter, Stan It has been 400 years since the last supernova within our Galaxy. The closest supernova during modern times was SN1987A at a distance of 160,000 ly in the Large Magellanic Cloud. Supernovae, one of the most energetic aophysical phenomen a known (possibly second only to gamma-ray bursts) and their associated expanding remnants have long been thought to be the accelerator, and possibly the source, of Galactic cosmic rays. Supernovae are also the birthplace of neutron stars, and, for a mass ive progenitor, a black hole. We propose a pointed, target-of-opportunity observation with the EGRET inument toward any Galactic supernova occurring during Cycle 8. The high-energy gamma-ray data obtained from this observation, when combined with other multi-wavelength observations, would lead to a deeper understanding of this phenomenon.
GRO-98-151 Murphy, Ronald OSSE has made fundamental contributions to flare science including the following: accelerated ions contain more energy than electrons; the accelerated alpha/proton ratio is high; processes at >10 MeV have time scales as short as 0.1 s; and the composition of the ambient plasma may change during the flare. Continued progress in flare science requires increased solar exposure which can only be achieved by dedicated observations of the Sun. If no X-axis target with higher scientific priority is selected, we propose that the Sun be designated the OSSE secondary source (X- axis). We further propose to maximize OSSE solar exposure by requesting that the Cycle 8 viewing plan be optimized so that the Sun is positioned within 10 deg of the X-Z plan e whenever possible, allowing OSSE to slew to the Sun in response to a BATSE trigger. This proposal complements two other proposals requesting CGRO-wide solar observations on the Z axis with both dedicated and Target-of-Opport
GRO-98-155 Kinzer, Robert Measurement of the cosmic diffuse gamma-ray background (CGB) is one of the original science goals of OSSE. OSSE provides a capability, unique now and into the forseeable future, to observe this fundamentally important radiation. As outline d in the initial multi-year proposal submitted and approved in cycle 7, a large data base collected over the full range of background parameter space is needed to be able to isolate the cosmic diffuse flux from other locally produced backgrounds. The curr ent proposal is for the second year of that multi-year proposal to acquire an adequate data base to measure both the spectrum and isotropy of this radiation. Preliminary results from the first portion of the Cycle 7 observations are encouraging, and confi rm the expectations of the proof of concept measurements made prior to cycle 7. The inument is able to perform the complex and extended large-offset observations using two types of shutter; results confirm the two different
GRO-98-156 Dennis, Brian We propose to continue providing easy on-line access to the BATSE solar flare data at Goddard's Solar Data Analysis Center. Our facility contains a continuously updated archive of all BATSE solar flare data since launch together with an ex tensive package of data analysis software. It is used extensively by the solar physics community for scientific analysis of the X-ray observations themselves, for correlative analysis with observations at other wavelengths, and to identify times of hard X -ray flares. The requested funding will be used for three part-time people - a data technician to continue logging BATSE data and recording flares, a programmer for software support, and CoI Richard Schwartz to provide science support.
GRO-98-157 Vestrand, W. Thomas We propose a Compton Observatory ToO program, in collaboration with groups operating the leading TeV gamma-ray telescopes in the Northern and Southern Hemispheres, to simultaneously observe the gamma-ray properties of TeV gamma ray emittin g Blazars during intense x-ray flares. Our targets are four, highly variable, X-Ray-Selected BL Lacs that are known TeV gamma-ray emitters: Mrk 421, Mrk 501, PKS 2155-304, and PKS 2005-489. The gamma-ray observations will be supported by simultaneous sate llite observations at x-ray energies and by ground-based observations at radio and optical wavelengths. The observational campaign will be triggered by the detection of a major x-ray outburst from one of the objects with the All-Sky Monitor on RXTE. The C ompton Observatory measurements, in conjunction with our multiwavelength campaign, will help resolve some of the important puzzles associated with blazar phenomenology.
GRO-98-158 Macomb, Daryl The second EGRET catalog and supplement list 98 sources of high-energy gamma-rays of unknown origin. Little is known about these sources despite their importance to gamma-ray aonomy. We propose to explore the low-energy gamma-ray behavi or of six of these sources using the OSSE and COMPTEL inuments. We have used some simple criteria to identify several candidate sources and have used the calculated high-energy spectra to extrapolate down into the low-energy gamma-ray range. Each of th e six candidates is likely to be detected by OSSE and possibly by COMPTEL. Extending the observations of these sources to lower energies is an important step in addressing the characteristics of this class of gamma-ray source.
GRO-98-161 Valinia, Azita We propose to determine the scale height of the Galactic diffuse emission in the hard X-ray/soft gamma ray band via simultaneous RXTE/OSSE observations. To understand the origin of the diffuse emission, determination of its scale height is necessary since comparison of the measured value with that expected from candidate radiation mechanisms (e.g. inverse Compton scattering, non-thermal electron/proton bremsahlung) will provide a testbed for the different scenarios of the origin of the emission. These observations need to be simultaneous so that hard discrete sources (many of which are variable) can be detected via the small fov and hard X-ray sensitivity of RXTE. Their contribution can then be estimated and subtracted from OSSE's spect rum. This proposal builds on our cycle 7 investigation where we performed simultaneous RXTE/OSSE observation of the Galactic plane at zero latitude.
GRO-98-164 Miller, H. Richard We propose an OSSE observation of the X-ray bright Seyfert 1 galaxy Akn 120, to be conducted simultaneously with our approved RXTE pointing. These observations will yield one of very few truly simultaneous X-ray/gamma-ray spectra for Seyfe rt 1s. This is extremely important due to the highly variable nature of these objects. The resulting well-determined X-ray/gamma-ray spectrum will allow a precise measurement of the reflection component already detected in the Ginga data, but the extended bandpass will measure the high-energy cutoff (and a possible non-thermal component) and to compare it with those found for other Seyfert 1 galaxies.
GRO-98-166 Ryan, James We propose to conduct spectroscopic analyses of COMPTEL solar flare data and to use those results to analyze individual flares. We can now deconvolve complex solar flare spectra from both our telescope and our burst spectrometer inument s within COMPTEL, using a Maximum Entropy method. We wish to explore other Bayesian methods and to deconvolve spectra jointly for both COMPTEL and OSSE inuments in a rigorous fashion. The photon fluxes derived in this manner can be used to analyze flar es that exhibit anomalously soft proton spectra. We have contructed a photospheric, analytical, neutron transport model that can be used effectively for low energy neutrons. The 2.223 MeV line from thermal neutron capture in the photosphere can be combine d with the results of low-threshold-energy line fluxes (e.g. 20Ne) to derive the proton spectra. These proton spectra, if soft enough, can carrry far more energy than energetic electrons in flares.
GRO-98-168 Kinzer, Robert Simply configured deep observations of the galactic plane toward the center with OSSE provide a direct means for mapping the diibution of 511 keV and positronium continuum positron annihilation components in both latitude and longitude. This basic method provides a direct mapping approach which can well-measure the shape of the galactic bulge and ridge. It has a considerable sensitivity advantage over other techniques because it uses both the half-MeV line and the ~4.5 times more intens e positronium continuum fluxes rather than just the line flux. The current sparse data set of properly configured and deep measurements shows a sharp central bulge which is best characterized as a ~24 deg.FWHM Gaussian bulge in longitude with an ~25% cent ral discrete source contribution. The current proposal is for deep ''basic'' observations in crucial regions at 5 deg., 355 deg,, and 335 deg. longitudes where no credible measurements currently exist.
GRO-98-169 Esposito, Joseph For many years it has been believed that the acceleration of Galactic cosmic rays is due to the ong 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 non -exclusive data rights to 21 supernova remnants.
GRO-98-997 PUBLIC ToO This is a requested target of opportunity observation of XTE J1550-564 based upon RXTE monitoring of this source.
GRO-98-998 Unowned This is an observation, usually involving OSSE, which has been scheduled because no other proposed source currently fits into this slot.
GRO-98-999 Instrument teams This observation of the CRAB PULSAR is a calibration observation.