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 observations 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. Unfortunately, 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 9 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.
We propose to maintain and continue to upgrade the on-going Rapid Gamma-Ray Burst Response (RBR) program of COMPTEL, CGRO's 1-30 MeV imaging telescope. This largely automated system is capable of broadcasting 1-2 degree localizations of MeV-bright GRBs that take place within the ~1 steradian FoV of COMPTEL. These broadcasts are made via the GCN network to a world wide network of observers covering the entire elecromagnetic spectrum. These broadcasts can be made within ~8 minutes of the burst trigger under good conditions (c.f., GRB 980124) or within ~45 minutes for those events that require some level of manual intervention (c.f., GRB 980329). The resulting MeV light-curves and location contours are posted both to the WWW and to an anonymous ftp site. We are currently upgrading the RBR system with the goal to provide a response time in the range of 2-4 minutes. Past experience indicates that the RBR system can provide useful results on 3-5 bursts per year.
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 important 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 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 of 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.
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 ideal laboratory for studying these important astrophysical 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).
We propose (1) to continue to operate the BATSE Coordinates Distribution Network (BACODINE), & (2) agressively pursue new customers and modify the operation to meet the customer's needs. BACODINE (a subsection of GCN) 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 (<6 sec) while the GRBs are still bursting. The ROTSE contemporaneous detection of GRB990123 using a BACODINE location has proven the viability & effectiveness of BACODINE at even shorter time delays than the SAX-based follow-up observations. Continued operations will allow for more counterpart identifications and increase our understanding of GRBs.
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 emission in lower frequency bands. The objective of this work is to quantify the time delay of correlations between short-term (~day) variations in different bands, and thus to place limits on possible emission mechanisms. The objects selected for consideration have demonstrated previous bright GeV gamma ray flares. A ToO trigger could arise from exceptionally bright and rising in the optical flux; 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. In that case, we propose to share the ToO extension data with the PI for the scheduled observation.
We propose to continue the work of the 3rd Interplanetary Network, which now includes BATSE, Ulysses, and the Near-Earth Asteroid Rendezvous missions, among others. About 1 burst is detected and triangulated by two spacecraft every 4 days, and about one burst/week is detected and triangulated by 3 widely separated spacecraft when NEAR is recording data. The latter error box areas are often comparable to or smaller than those of the BeppoSAX WFC. The data on GRBs and SGRs will be circulated via the GCN, placed on our web site, and published in catalog form. We will also add Mars Surveyor Orbiter 2001 to the IPN. This effort continues to support a large community of scientists (60 to date) who request IPN data for special projects, often requiring special formats and/or data processing. Hence the 'Service Proposal' aspect.
In this joint proposal by all CGRO instrument teams, a target of opportunity observation with all four CGRO instruments is proposed to measure the spectrum of the nearest active galaxy Centaurus A in a state of strong gamma-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 tests of hypotheses concerning 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.
Detection by COMPTEL of the ~ 700 year-old optically unobserved supernova remnant confirmed $^{44}$Ti viability to uncover hidden Galactic supernova remnants. Published results on the $^{44}$Ti line emission from RX J0852-4622 are based on the observations performed with COMPTEL before second CGRO reboost. Unfortunately, very few observations were performed with the pointings close enough to the position of RX J0852-4622. This certainly has affected the quality of our spectral and imaging analysis of this exciting object. We propose to perform dedicated observations of the GROJ0852-4642 region that minimize possible systematic background variations, yet provide a source exposure at several aspect angles, hence reducing response inaccuracies. A special aspect of this proposal is to determine the extent of the statistical background fluctuations impact on the resulting spectrum of the RXJ0852-4622/GROJ0852-4642.
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 analysis rules are not optimized for the poorer quality data. By changing the rules used by the data analysts, we can recover a significant fraction of the lost events, allowing improved statistics for detection and study of sources. These changes can help all users obtain maximum scientific return from the EGRET data. We propose to continue an event recovery program for viewing periods chosen by a survey of the CGRO user community.
We propose a Target of Opportunity Observation of a nearby X-ray selected BL Lac object with CGRO in combination with the Whipple Observatory gamma-ray telescope and the Rossi X-ray Timing Explorer when the object is in a high emission state. 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 emission 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 be detected with multiple telescopes is high. Such an observation provides an excellent test of blazar emission models. We submitted very similar proposals in Cycles 7 and 8 that were accepted, \ but so far the ToO criteria have! not been met.
Localizations and redshifts of several GRBs when combined with their logN-logS relation show a strong influence of the dispersions of the intrinsic properties, while claims for time dilation or hardness-flux correlations point to cosmological signatures. We propose to investigate the intrinsic versus cosmological signatures of GRBs using the distributions of-and the correlations between-the parameters describing their strengths, pulse profiles and spectra. A bias free determination of these distribution requires the knowledge of data truncations. We have developed methods for determining this for any measured quantity, some of which may suffer from complex truncations. We have also developed methods to account for these complexities. The results will be useful in setting limits on models, determining the cosmological evolution, and the designs for future missions.
As a continuation of an accepted Cycle 8 proposal, 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 9 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 may be found to be merely an extension to the already well-determined log-normal distribution 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.
We propose simultaneous COMPTEL, OSSE and RXTE observations of the gamma-ray source GRO J0516-609, which is the second MeV blazar candidate after PKS 0208-512. The science goals of the proposed observations are to determine the spectrum at hard X-ray / soft gamma-ray energies, where the spectral shape is yet basically unknown, to test for hard X-ray / soft gamma-ray variability in flux and spectral shape, and to identify the counterpart of GRO J0516-609.
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 support center.
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 results from the annihilation of positrons, emitted by some radioactive nuclei (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 instrument to detect this emission. A systematic search in BATSE background data is under way and we ask now for a renewal proposal in order to continue it, as well as to analyze the new novae during the upcoming cycle. Data analysis techniques previously applied for BATSE observation of 511keV transients of short duration and occultation observations that have been optimized for this study will! be used.
COMPTEL's 26Al map shows that the extended 1.809 MeV emission in the Vela region peaks at l~267 . A unique calibration of nucleosynthesis models for the 26Al source types is possible here, recently-revised distances being ~250pc only: 11000 year-old Vela Supernova should validate core-collapse supernova yields, g2 Velorum should be detectable from Wolf-Rayet 26Al predictions. Additionally, a newly discovered X-ray remnant and its possible 44Ti radioactivity hold promises for unique constraints. Previous Observations of the Vela region (41 days, 33 pointings) are mostly at large aspect angles (17 at >25 ). Ignoring special pointing requests limited the cumulative sensitivity. We propose dedicated observations of the Vela region to effectively double the exposure. The proposed systematic 'dithering' of the pointing axis will help that previous data can be analyzed with better sensitivity, effectively adding value beyond the additional observation time requested h! ere.
We propose a detailed temporal and spectral analysis of BATSE Gamma-Ray Burst (GRB) tails to search for signatures of the early high-energy afterglow as predicted in the internal/external shock fireball model. Recently it has been suggested that the forward external shock is capable of producing emission in the BATSE energy range that decays as a simple power law and whose spectrum evolves according to the cooling synchrotron spectrum. We model the temporal behavior with a power law function and characterize the spectral evoultion by modeling the spectra with a smoothly broken power law. In addition we apply a model-independent Color-color diagram (CCD) technique to identify spectral evolution trends in accordance with the evolution of the synchrotron spectrum. We are especially motivated by GRB980923, for which strong evidence exists for an early high-energy afterglow not unlike the afterglow properties observed at lower energies of afterglow GRBs.
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 spectral 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 the expectation that other large flares will add new insights, we propose to analyze all Phase 9 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 requested under specific circumstances.
The nature of the unidentified gamma-ray sources remains an important open question after eight years of CGRO observations. We have found a new unidentified source with unusual properties -- a steep spectrum in the EGRET energy range, a strong spectral flattening in the COMPTEL range, and some evidence of time variability. There have been no useful OSSE observations of this source. In order to characterize this source more fully, we propose the first OSSE observations and additional COMPTEL observations, along with continued archival analysis of COMPTEL and EGRET data.
We propose to continue our project - sucessfully started in CGRO Cycle 8 - of simultaneous Gamma-ray and X-ray observations of selected, time-variable blazars. The main goal is to simultaneously determine their high-energy properties, with emphasis on the relationship between X-rays and Gamma-rays (e.g. correlation between spectral slope in X-rays and the Gamma-ray intensity). It can be achieved by comparing source measurement covering different intensity and spectral states in X- and in Gamma-rays. A first set of such simultaneous measurements has already been obtained in Cycle 8. With OSSE and COMPTEL we want further monitor the longterm behaviour of these sources to derive improved informations on their emission characteristics at high energies like duty cycles, time and spectral variability. Such informations are crucial for our understanding of the emission processes in blazars, and e.g. for estimates about their contribution to the extragalactic Gamma-ray! background.
We propose coordinated optical/UV/gamma-ray observations of BL Lacertae covering the entire range from optical frequencies to TeV gamma-ray energies, using the OM and the EPIC of XMM, RXTE PCA and HEXTE, CGRO OSSE and COMPTEL, and the HEGRA and CAT Cherenkov telescopes. Science goals of our observations are to constrain the high-energy cutoff of the low-frequency component of the broadband spectrum of BL Lacertae, to measure the hard X-ray spectrum and its turnover towards MeV energies, and to provide for the first time a truly simultaneous measurement of the high-energy component of its spectrum up to TeV energies, potentially posing strong constraints on currently popular emission models for blazar-type AGNs.
During the first 8 years of its operation, BATSE detected recurrent emission from two of the three known SGR sources, SGR 1900+14 (twice) and SGR 1806-20 (thrice), and discovered the first new SGR in more than 18 years, SGR 1627-41. The most recent reactivations of the two known sources initiated TOOs with RXTE, which resulted in the unambiguous detection of strongly magnetized (B>1E14 G) pulsars associated with each SGR, which strongly supports the magnetar model for SGRs. The discovery of SGR 1627-41 initiated a TOO with BeppoSAX, which led to the discovery of a persistent X-ray counterpart. We propose to continue our succesful SGR project by: (i) reporting the existence and emission properties of any new SGRs, (ii) performing detailed statistical studies of SGR burst temporal and spectral properties, (iii) investigating the evidence for hard emission from SGRs and (iv) searching for evidence of Global Seismic Oscillations following SGR bursts in the BATSE data.
We propose a deep OSSE observation of the black hole candidate LMC X-1 in Compton Cycle 9, in conjunction with RXTE observations. The goal is to pin down the nature of the spectrum above 100 keV, to construct a broadband spectrum, and to study its short term spectral variability. The result will be useful for discriminating competing accretion disk models of persistent black hole X-ray sources.
Due to the rare opportunity to observe the strong activity of GRS 1915+105, our cycle 8 approved six week CGRO/OSSE observation of Cas A SNR was cut to three weeks. The goals of the Cas A observation is to confirm the COMPTEL detection of Ti44 gamma-line flux from the Cas A supernova remnant with a 3sigma detection, extend the range of the detected hard X-ray continuum to a higher energy, and possibly to detect the cut-off energy of synchrotron emission of accelerated electrons near shock fronts in Cas A. We propose a nine week OSSE 4-detector Cas A observation to obtain a 3sigma detection of Ti44 decays with a flux of 3.3e-5 ph/cm**2/s in the 68 & 78 keV and 1.16 MeV lines.
We propose to use COMPTEL and OSSE to measure gamma-ray lines and hard X-ray continua to clarify the mechanisms, nucleosynthesis, and dynamics of sufficiently nearby supernovae. The requested observations vary from single early tests of a specific hypothesis, for relatively distant SN Ia, to extensive observations lasting months for Galactic events. We define the Target of Opportunity criteria in terms of distances, and convert these to observable quantities where possible.
We propose CGRO/OSSE observations in Vela to confirm the COMPTEL detection of 44Ti line emission from that region, to test whether the possible X-ray supernova remnant RX J0852-46 is the source of that emission, and to help determine better the flux in the gamma-ray lines. These data will also help to answer the question whether the 1.8 MeV signal from that region is concentrated in that remnant. We request eight weeks of OSSE exposure, two of which should be obtained in Cycle 8, to achieve these objectives.
We propose to observe the next classical nova of each class, CNO-rich and Ne-rich, which is convincingly at a distance less than 2 kpc. We will observe with OSSE for 3--4 weeks during the first month after outburst to search for 478 keV gamma-rays from 7Be decay and for a total of 4 weeks with both OSSE and COMPTEL at roughly six months after outburst. This latter observation is to search for 22Na decay photons at 1275 keV (and associated positron annihilation photons) when the entire ejected shell is quite thin to gamma-rays.
The final report of the latest Astrophysics Senior Review indicated that the extended CGRO mission was, in part, motivated by the recognition that "CGRO will be an important observational tool during the upcoming solar maximum." COMPTEL provides unique capabilities for studying both 0.1-30 MeV solar flare gamma-rays and 20-200 MeV solar flare neutrons. With the next solar maximum expected to take place during Cycle 9, it is imperative that we maximize our exposure to the Sun during this time. Long, uninterrupted exposures to the Sun offer many advantages over the use of ToO s. Our proposal provides several means of achieving prolonged solar exposures with COMPTEL (as well as OSSE and EGRET) while, at the same time, providing useful non-solar data. The principle part of our proposal is to observe the Sun during three 6-week observations that also provide improved all-sky coverage for COMPTEL. In addition, we propose several strategies for further solar observati! ons during Cycle 9.
Gamma-ray bursts observed by BATSE have a surprisingly narrow distribution of Epeak, where Epeak is the energy at the peak of the nu-Fnu energy spectrum. It is been suggested that the intrinsic Epeak distribution is actually much broader, but that a Malmquist-like bias reduces the BATSE trigger efficiency for hard bursts. We propose to test models of the intrinsic Epeak distribution by a search for bursts that trigger on BATSE discriminator channel 4, which is sensitive to photons above 300 keV.
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 about 110 strong hard X-ray/soft gamma-ray sources and occasional followup/characterization of new or unusual transient behavior with the Large Area Detectors in the 20 keV to 2 MeV energy band. Beyond the quick-science analysis activities of the EOT, we propose to: (1) develop a real-time transient search algorithm to be placed at GSFC, (2) apply a new physical background model to improve monitoring sensitivity, and (3) refine the imaging technique.
We propose to use BATSE SD, LAD, RXTE/ASM data to construct a 1-50 keV light curve of the LMXB Sco X-1. The level of activity in this system dramatically increases with energy. Using the combined dataset this phenomenon will be investigated. Other correlated episodes of high energy activity will also be identified and quantified. This type of study is unique. It has never before been possible to study a LMXB over the energy and temporal range that will be done here.
The reported detection of variable gamma-ray emission from a small number of active galaxies with the CGRO/COMPTEL instrument has been cited as evidence for a potential new class of AGN: ``MeV Blazars.'' Their emission properties appear distinct from those associated with the many high-energy blazars catalogued by the EGRET instrument. Since their announced detection during the early phases of the CGRO mission, however, none of these objects has been redetected with any significance, implying a short duty cycle for such active MeV behavior. Here, we propose to revisit the question of MeV emission from the two original MeV-blazar candidates. We will employ the latest COMPTEL analysis software, event-selection criteria, background models, and response functions in a comprehensive reanalysis of all available archival data. Our objective is to more firmly establish or reject the claim of MeV emission from these objects.
The giant outbursts of GeV emission observed from some blazars pose a significant challenge to our understanding of blazar emission mechanisms. Unfortunately, the giant outbursts of GeV emission from blazars are not always predictable from observations in other energy bands. We propose a ToO program to search the sky for intense outbursts of GeV emission which optimally utilizes EGRET spark chamber gas and has minimal impact on the CGRO observing schedule. Specifically, we request 1-day activation of the spark chamber for no more than 14 CGRO high galactic latitude pointings when EGRET is nominally scheduled to be turned off. Our tests on recent EGRET data indicate that a 1-day snapshot can unambiguously detect bursts out to nearly 15 degrees from the CGRO pointing direction when the >100 MeV flux exceeds 10^-6 cm^-2 s^-1. If a major outburst is detected, a follow-up multiwavelength campaign will be conducted to follow the burst development.
We propose to improve the accuracy of the BATSE locations automatically generated by LOCFAST in near real-time. These locations are disseminated over the Internet as part of the GRB Coordinate Network (GCN). The BATSE location software of the GCN has recently been upgraded, creating the program LOCFAST. The program used for generating the catalog locations, LOCBURST, has proven capabilities---in the first 7 years of operation 317 GRBs were located with accuracies (statistical and systematic) of 2.5 degrees or better. We have identified six areas in which LOCFAST can be improved. The proposed improvements to LOCFAST (and LOCBURST) include a more accurate spectral model and the generation of elliptical error boxes. We aim to provide locations of better accuracy in near real-time with the goal of increasing the probability of prompt counterpart detections.
We propose to continue our Cycle 8 project to produce and maintain 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 standard model functional fit parameters with various combinations of time and energy resolution. The catalogs will be disseminated via the World Wide Web, and will be updated regularly as new burst data come in.
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 the 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.
This is a Compton cycle 9 Guest Investigator Proposal for the renewal of cycle 8 grant NAG 5-7980. It concerns the analysis and modeling of GRB continuum spectral evolution data obtained by BATSE. This project is an ongoing collaboration between Rice University and the BATSE instrument teams. Following the major developments of these past two years, we will focus in cycle 9 on X- and gamma-ray spectral evolution properties that are most relevant to the multiwavelength (radio - X-rays) behavior of GRBs and their afterglows, and critical tests of the different emission models. This is the core research project of our group at Rice.
The bimodal nature of the GRB duration distribution shows that there are two classes of GRBs: short and long. Many studies have shown that short GRBs have higher hardness ratios than long GRBs--we propose to better characterize the differing spectral properties of short and long bursts by a high-resolution spectral analysis of the short events. Such studies have not yet been conducted because of two difficulties: short GRBs have low fluences and most spectral analyses have used datatypes unsuited to the analysis of short events. We shall overcome the first difficulty by summing many events. We shall use the only suitable BATSE datatype, the time-tagged events from the Spectroscopy Detectors. These STTE data provides high spectral and temporal resolution coverage extending to several seconds before and after the trigger time.
We propose a multiwavelength X-ray/gamma-ray campaign for NGC 4151, the brightest radio-quiet Seyfert 1.5. The determination of its intrinsic spectrum will test the unified AGN model, according to which Seyfert 1.5s contain the same intrinsic source as Seyfert 1s but seen through an obscuring medium. Continuing monitoring of NGC 4151 is also likely to reveal changes of the flux level in that source, which have been observed in the past, but not yet by OSSE. The OSSE observation will be accompanied by simultaneous observations by XMM (proposed) and XTE and SAX (to be proposed). The resulting precise determination of the broad-band spectrum will allow us to determine the geometry of the source together with radiative processes responsible for production of X-rays and gamma-rays.
We propose to conduct CGRO-wide ToO observations of the Sun as we approach solar maximum, requesting up to three such ToOs during Cycle 9. Each ToO would be triggered by NOAA solar activity forecasts. The only other CGRO solar ToO (June 1991) yielded 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 instrument 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 Wide We! b.
The general method developed to measure the CDG emission (Kappadath 1998) is now a proven alternative method for analyzing other sources of diffuse emission in COMPTEL data. The goal of this proposal is to continue our CDG analysis effort and to extend the technique to other sources of diffuse radiation. Specifically, we propose (1) to independently measure the diffuse spectrum of the inner Galaxy using the CDG analysis technique; (2) to investigate the origin and isotropy of the CDG emission by computing and comparing the CDG spectrum from independent pointing directions; and (3) to measure the albedo atmospheric gamma-ray emission.
The Compton attenuation theory of gamma-ray bursts has successfully passed three observations tests: the correct fit of observed spectra, the correct prediction of an x-ray excess, and the correct derivation of gamma-ray burst redshift values. We propose to continue testing the model. This will be done in several ways. First, we will fit the model to time-series of burst spectra. Second, we will fit the model to very broad spectral ranges by combining BATSE data with data from BeppoSAX and Comptel. Third, we will derive the redshifts of burst seen optically by fitting the gamma-ray spectrum, comparing the gamma-ray redshift to the optical redshift. Fourth, we will model the E-peak distribution expected for the theory and compare the model to the observations.
In 1998, the observation of a giant periodic flare with a hard peak from SGR 1900+14, the discovery of a new SGR 1627-41, and the association of these sources with slowly rotating possibly highly magnetized neutron stars have radically expanded our knowledge about the soft gamma-ray repeaters. In previous cycles we have been performing spectral fitting and theoretical studies of the SGR bursts seen by BATSE. As part of this effort, we have been generating light curves and spectra using simple models. This past year, we realized these would be very useful for the community as a whole, to save them reprocessing all the bursts to find ones that are particularly interesting. 1998 saw an unprecedented activity from three sources, and there are now over 200 BATSE SGR triggers. Here we propose to complete and publish our catalog of BATSE bursts. We propose to put this on the WWW, and continually update it. We request non-exclusive data rights to the BATSE data from any new bursts in Cycle 9.
We propose to make a joint spectral analysis of GRBs in the BATSE database which are located within the fields of view of either the SAX WFCs or the ASM on RXTE. The very broad-band coverage obtained this way will allow us to test physical models of GRB spectra, determine the number and energy distribution of spectra breaks, test whether X-ray tails are a separate emission component or result from spectral evolution of the main component, and investigate the relation between the spectral softening seen in many GRBs and GRB afterglows.
Using a rapid slewing response system to promptly observe burst positions calculated on-board CGRO by BATSE, the OSSE instrument has discovered persistent emission >100 keV with power-law decays from several gamma-ray bursts. This demonstrates OSSE's unique capability to extend the study of burst afterglows to the primary energy range of the burst itself, and at times near to the trigger (10--100 s). 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, and provide a strong test of the blastwave models and the internal/external shock paradigm.
We propose the `Pure Physical Parameterization' Project (the P^3 project), which will characterize the temporal and spectral properties of 800 bright BATSE GRBs. Both instrumental and cosmological redshift effects will be removed from the characterizations. To remove the detector properties we will deconvolve the observed count rate time histories into light curves and spectra of photons by robust and non-biased procedures. To bypass the effects of cosmological redshifting, we will base the energy bands and time intervals used for the deconvolutions on physical features present in the light curves and photons spectra themselves. To constrain the properties of emitters, we will compare temporal and spectral signatures of intensity groups of the 800 bursts with a reference sample of events with known redshifts. We will test models of emitters with and without evolution by using appropriately de-redshifted signatures of bursts.
One of the most energetic astrophysical events is the supernova explosion. Since the advent of space based instrumentation the nearest supernova event to be observed has been SN 1987A in the Large Magellanic Cloud (50 kpc). A Galactic supernova would provide an unprecedented observational opportunity for modern space and ground based instruments and a preferred target of opportunity for the Compton Gamma Ray Observatory. We anticipate that observations of a galactic supernova would occur simultaneously across the entire spectrum from radio through gamma rays (including OSSE and COMPTEL) and would continue for several years. The scientific return from multi-wavelength observations of a Galactic supernova would lead to a deeper understanding of this astrophysical phenomenon. We request that an EGRET Target of Opportunity be declared if a supernova event occurs within the Milky Way Galaxy and that repeated observations be performed.
EGRET has observed the highest energy emission from a gamma-ray burst. We request to continue observing GRBs with EGRET by using BATSE trigger to activate the EGRET spark chambers about once per month. We will also continue analyzing spectra above 1 MeV from the EGRET TASC. These high energy observations will be essential to place in perspective the contemporaneous observations of Milagro, a new TeV observatory ideally suited to making even higher energy observations of gamma-ray bursts. MILAGRO is operational 24 hours a day with a field of view of > 1 sr, unlike other ground-based TeV gamma-ray detectors with 5-8% duty factors and a few square degrees field of view. The fluence sensitivity of MILAGRO is as low as a few times 10^-7 ergs/cm2 for a 1 sec burst from zenith.
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 spectral and pulse-period evolution through the peak and decay portion of an outburst. This is a resubmission of an expired GRO Cycle 4-6 multiyear, Cycle 7, and Cycle 8 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.
We propose the combined spectral and temporal analysis of the black hole candidates Cyg X-1, GX 339-4 as well as a possible future X-ray transient source, with particular emphasis on the structure of the time lags between different energy bands, as a function of the Fourier period of variability. We have argued that such an analysis can uncover the radial density strcture of the hot corona responsible for the production of the high energy radiation through the Comptonization process. Our goal is to search for correlations between the density structure of the hot coronae with other parameters of these systems, e.g. their spectral states.
Positron annihilation radiation from the galactic center region was discovered nearly 30 years ago. Most observational results have related to the 511 keV line emission associated with positron annihilation. The OSSE instrument on CGRO has provided the first maps of the 511 keV emission, and the discovery of a surprising excess at positive galactic latitudes above the center of the Galaxy. Most of the annihilation emission is in a 3-photon continuum below 500 keV. Mapping this emission is of importance in order to confirm the features in the 511 keV maps and to study the annihilation sites through the ratio of the line to continuum emission. The continuum analysis is more difficult because of complications in the spectral fits from the diffuse galactic gamma ray emission from cosmic ray interactions, and from discrete sources. We propose the first efforts to map the positronium continuum emission.
We propose Target of Opportunity observations with BATSE, OSSE and USA 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 corresponds with X-ray spectral states. Long TOO observations give the highest sensitivity for emission above 511 keV -- which is difficult to explain in the X-ray high, soft state -- and increase the likelihood of observing spectral state transitions, which are known to have occurred in at least four BHCs. State changes are still not well studied in gamma rays.
OSSE observations at galactic l=95 found a spectrum similar to the diffuse emission from the GC region but reduced by a factor of 4. The OSSE data could not distinguish between diffuse emission and contribution from a number of point sources. BeppoSAX recently observed the galactic plane at l=95 to disentangle the origin of this high-energy excess, and clearly detected (10 sigma) emission in the PDS (15-100 keV). MEDS data (2-10 keV) showed that no single point source is responsible for the detected emission which is, thus, truly diffuse. The origin of the emission, thermal vs. non-thermal is then raised. To further these studies, three additional 50000-second Beppo-SAX observations observations have been approved for the AO3 period, to be conducted simultaneously with OSSE. We request OSSE observations to support these correlative observations.
We propose to simultaneously observe the bright Seyfert I ESO141-G55 with BeppoSAX and OSSE to measure its high energy spectrum and constrain the high energy spectral cut-off. This object is selected based on its flat spectrum and high flux in the 2-10 keV band (F > 1e-11 erg cm-2 s-1), assuring a good signal-to-noise ratio up to 200 keV. The main goal is to measure the high energy cut-off as expected in this class of AGNs. The precise detection of the cut-off energy, so far published for only three sources, is crucial for our understanding of the emission processes occurring in the innermost region of Seyfert galaxies.
Mrk 231 is a low ionization broad absorption line QSO, an ultraluminous infrared galaxy, and (as indicated by its tidal tails) may be influenced by galaxy interactions or merging. After correcting for extinction, the central nuclear source of Mrk 231 is revealed to be one of the intrinsically brightest nearby AGNs. An OSSE dectection of Mrk 231 would provide insights into several aspects of AGN phenomenology: It would substantiate the universality of the existence of quasi-isotropic X-gamma emission from AGNs over a wide range of luminosities. It would help us understand the ionization state and hence the dynamics of the broad absorption line region by allowing us to infer the underlying X-ray spectrum. Lastly, and perhaps most significantly, an OSSE detection would support the hypothesis that AGNs are created in galaxy interactions and would point towards low ionization BAL QSOs as a population of newly formed AGNs.
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.
OSSE mapping of the galactic 511 keV positron annihilation radiation has detected strong bulge emission, weak disk emission, and an enhancement of emission at positive latitudes. We propose to observe the inner portion of the Galactic Plane -38 deg < l < 38 deg for 28 weeks during Cycle 9, significantly improving OSSE observations of the weak disk emission along the inner radian of the Galactic Center (GC) region. Establishing the longitudinal profile of this emission will permit comparison with maps at other wavelengths and give insight into the sources and annihilation sites of Galactic positrons. The proposed observations have been coordinated with the OSSE solar team and the COMPTEL team, to permit all three observing plans to be simultaneously achieved. By having the S/C x-z plane follow the Sun along the ecliptic, Cycle 9 provides an excellent opportunity to substantially improve OSSE exposure along the galactic plane.
We propose a broad, flexible program to provide at least 63 weeks of OSSE Solar access during CGRO Cycle 9 which covers the peak of Solar Cycle 23. Using previous OSSE solar-flare data, we have made fundamental contributions to flare science in areas such as ambient abundances, accelerated-particle energetics, and, most recently, the composition of flare-accelerated particles. With the extensive solar coverage proposed, we can achieve our goals of providing OSSE flare data to the solar community, analyzing new flare data, supporting HESSI after its expected launch in 2000, and making coordinated observations with other instruments such as Yohkoh and ACE. This can be accomplished by a combination of observing strategies including designated observations, 1-hour responses to BATSE solar triggers, and solar Targets of Opportunity. We give examples of how considering the solar position when scheduling celestial observations can help achieve this goal.
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 measure the isotropy and spectrum of this fundamentally important radiation over the energy band between 40 keV and ~1 MeV. As outlined in the initial multi-year proposal accepted 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. Observations at a minimum of six orthogonal directions are needed to measure its isotropy. One of the basic observations in Cycle 7 (in the apex direction of the cosmic microwave background radiation) was bumped by a ToO observation. The observations proposed here include that observation. Together with scheduled Cycle 8 observations, the proposed observations will complete the minimal data set.
Late light curves of Type Ia supernovae suggest that a fraction of the positrons produced in $^{56}$Co decays escape the ejecta and annihilate on longer timescales. The confirmation of this escape lies in the detection of 511 keV annihilation radiation from a Type Ia SNR. Two nearby SNRs, SN 1006 and the Lupus Loop, have been suggested to be the remants of Type Ia SNe. The smaller remnant, SN 1006, is located within the larger Lupus Loop, making both remnants observable as a single target for OSSE. We propose to use OSSE to observe the Lupus Loop/SN 1006 region for 4 weeks in cycle 9 to detect 511 keV line emission with 4$\sigma$ confidence. This delayed annihilation, if observed, would contribute to the study of SN explosion physics, the use of SNe as standard candles and the physical interpretation of 511 keV maps.
We propose a comprehensive search for transient sources of gamma-ray emission above 100 MeV. While the 3rd EGRET catalog lists 271 sources, most of these are either steady sources or very bright in a single CGRO viewing period. Using data above 1 GeV, we have discovered many new sources which are seen weakly in more than one viewing period. We will extend our work to energies above 100 MeV to look for similar sources which are transient on the timescale of weeks. A large increase in gamma-ray transients is expected based on our 1 GeV results. A further search for variability on shorter timescales will also be pursued.