The Compton Gamma-Ray Observatory was launched on April 5, 1991, carrying the imaging Compton telescope COMPTEL. Since its activation on April 25, 1991, COMPTEL has observed several gamma-ray bursts in its 1-sr field of view. The strongest of these bursts was observed on May 3, 1991. Event data over 0.8 MeV to 30 MeV as well as time resolved spectra over 0.1 MeV to 10 MeV have been recorded. For the first time, a direct single-telescope MeV image of a cosmic gamma-ray burst has been produced. The burst is located at (l,b) = (171.8 deg, 6.4 deg) with a statistical uncertainty (99 percent level) of about 2 deg. The systematic error is about 1 deg, due to the location of the burst near the edge of the COMPTEL field-of-view. Spectral analysis indicates that GRB 910503 is a 'classical' hard burst, with power-law emission up to several MeV, showing 'hard-to-soft' spectral evolution in its light curve.
Astronomy and Astrophysics
European Southern Observatory (ESO)
C. Winkler, K. Bennett, H. Bloemen, W. Collmar, A. Connors, R. Diehl, A. van Dordrecht, J.W. den Herder, W. Hermsen, M. Kippen, L. Kuiper, G. Lichti, J. Lockwood, M. McConnell, D. Morris, J. Ryan, V. Schönfelder, G. Stacy, H. Steinle, A. Strong, B. Swanenburg, B.G. Taylor, M. Varendorff, and C. de Vries, The gamma-ray burst of 3 May 1991 observed by COMPTEL on board GRO. 1992, Astron. Astrophys., v. 255, no. 1-2, pp. L9-L12.