The Locations of Gamma-Ray Bursts Measured by COMPTEL

The COMPTEL instrument on the Compton Gamma Ray Observatory is used to measure the locations of gamma-ray bursts through direct imaging of MeV photons. In a comprehensive search, we have detected and localized 29 bursts observed between 1991 April 19 and 1995 May 31. The average location accuracy of these events is 1.25\arcdeg (1$\sigma$), including a systematic error of \sim0.5\arcdeg, which is verified through comparison with Interplanetary Network (IPN) timing annuli. The combination of COMPTEL and IPN measurements results in locations for 26 of the bursts with an average ``error box'' area of only $\sim$0.3 deg$^2$ (1$\sigma$). We find that the angular distribution of COMPTEL burst locations is consistent with large-scale isotropy and that there is no statistically significant evidence of small-angle auto-correlations. We conclude that there is no compelling evidence for burst repetition since no more than two of the events (or $\sim$7% of the 29 bursts) could possibly have come from the same source. We also find that there is no significant correlation between the burst locations and either Abell clusters of galaxies or radio-quiet quasars. Agreement between individual COMPTEL locations and IPN annuli places a lower limit of $\sim$100~AU (95% confidence) on the distance to the stronger bursts.Comment: Accepted for publication in the Astrophysical Journal, 1998 Jan. 1, Vol. 492. 33 pages, 9 figures, 5 table

Relaxation of Radiation Effects on the Optical Transmission of Polymers

Changes in optical transmission of polymers over time were studied to determine the factors contributing to relaxation of defect states induced by intense radiation doses. Samples of low density polyethylene (LDPE), polyether ether ketone (PEEK), polypropylene (PP), and polyimide (PI) received doses up to 500 MGy from an 8 MeV electron accelerator. These doses were intended to simulate long-term exposure of common spacecraft materials in geosynchronous orbit. Features and absorption edges in ~250 nm to 1000 nm UV to IR transmission spectra can be related to energies associated with various defects previously observed in these highly disordered materials. Recent work has suggested that such radiation-induced defect states are sensitive to atmospheric exposure and that the radiation-induced effects would begin to relax. Upon prolonged exposure, the material would return to its original state. These findings have called in to questions the usefulness of many previous studies of radiation effects on spacecraft materials. After irradiation, transmission spectra were collected as soon as the samples were exposed to oxygen and water vapor in the atmosphere. Between irradiation and the time data collection began, the samples were stored in anaerobic environments. The spectra were collected periodically over several weeks in order to allow for accurate comparisons and to determine the relation rates and final equilibrium states

Monitoring the Low-Energy Gamma-Ray Sky Using Earth Occultation with GLAST GBM

Long term all-sky monitoring of the 20 keV – 2 MeV gamma-ray sky using the Earth occultation technique was demonstrated by the BATSE instrument on the Compton Gamma Ray Observatory. The principles and techniques used for the development of an end-to-end earth occultation data analysis system for BATSE can be extended to the GLAST Burst Monitor (GBM), resulting in multiband light curves and time-resolved spectra in the energy range 8 keV to above 1 MeV for known gamma-ray sources and transient outbursts, as well as the discovery of new sources of gamma-ray emission. In this paper we describe the application of the technique to the GBM. We also present the expected sensitivity for the GBM

The MeV spectra of gamma-ray bursts measured with COMPTEL

The past decade has produced a wealth of observational data on the energy spectra of prompt emission from gamma-ray bursts. Most of the data cover the energy range from a few to several hundred keV. One set of higher energy observations comes from the Imaging Compton Telescope COMPTEL on the Compton Observatory, which measured in the energy range from 0.75 to 30MeV. We analyzed the full 9.2 years COMPTEL data to reveal the significant detection of 44 gamma-ray bursts. We present preliminary results obtained in the process of preparing a final catalog of the spectral analysis of these events. In addition, we compare the COMPTEL spectra to simultaneous BATSE measurements for purposes of cross-calibration

The MeV spectra of gamma-ray bursts measured with COMPTEL

The past decade has produced a wealth of observational data on the energy spectra of prompt emission from gamma-ray bursts. Most of the data cover the energy range from a few to several hundred keV. One set of higher energy observations comes from the Imaging Compton Telescope COMPTEL on the Compton Observatory, which measured in the energy range from 0.75 to 30MeV. We analyzed the full 9.2 years COMPTEL data to reveal the significant detection of 44 gamma-ray bursts. We present preliminary results obtained in the process of preparing a final catalog of the spectral analysis of these events. In addition, we compare the COMPTEL spectra to simultaneous BATSE measurements for purposes of cross-calibration