Search for Compton-Backscattered Annihilation Radiation from the Galactic Center with OSSE
Abstract
An emission feature near 170 keV, interpreted as Compton-backscattered positron annihilation radiation, has been observed twice by balloon-borne germanium spectrometers from within ~ 15deg of the Galactic Center (Leventhal et al. 1978, ApJ 225,L11; Smith et al. 1993, ApJ 414,165). Upper limits on this feature set by HEAO-3 (Mahoney et al. 1993, A&AS 97,159) and other instruments indicate that it must be transient. A transient backscatter feature, along with unscattered annihilation radiation, was observed from Nova Muscae by SIGMA (Goldwurm et al. 1992, ApJ 389,L79), with a duration of a few hours. The Oriented Scintillation Spectrometer Experiment (OSSE) on the Compton Gamma Ray Observatory is particularly well-suited to search for such a feature. Since its launch in 1991, the OSSE instrument has observed the Galactic center region for ~ 160 days. Its energy resolution at 170 keV ( ~ 24 keV) is comparable to the reported widths of the backscatter peak (12-24 keV), and its 3 sigma sensitivity, ~ 3times 10(-4) photons/cm(2) /s at 170 keV for a 40000 s observation, would easily allow detection of the ~ 1times 10(-3) photon/cm(2) /s fluxes reported by the balloon instruments. We present the results of a day-by-day search of the available data and discuss the statistical compatibility between the OSSE data and the balloon observations.
- Publication:
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American Astronomical Society Meeting Abstracts
- Pub Date:
- December 1993
- Bibcode:
- 1993AAS...18311606S