Publication Date:
2011-08-24
Description:
The Gamma Ray Imaging Spectrometer (GRIS) was flown on balloons over Alice Springs, Australia on 1992 April 26 and May 7. A full Galactic center transit (about 12 hr) was achieved on both flights with the instrument working normally. The electron/positron annihilation line was detected on both flights. The line fluxes and line widths were found to be (7.7 +/- 1.2) x 10 exp -4 and (8.9 +/- 1.1) x 10 exp -4 photons/sq cm per sec and 1.3 +/- 0.7 and 3.6 +/- 1.0 keV, respectively. These results are compared to each other and earlier (1988) GRIS results to produce suggestive evidence for source variability. Near-contemporaneous OSSE/CGRO Galactic center observations indicate that the GRIS results cannot be due solely to a single point source like IE 1740.7-2942 within a few degrees of the Galactic center. The GRIS 1992 results represent the first time that successive high-resolution balloon measurements have been achieved on a time scale of days.
Keywords:
ASTROPHYSICS
Type:
Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 405; 1; p. L25-L28.
Format:
text
