Imaging Hard X-Ray/Gamma-Ray Observations of the Galactic Center Region

Recent imaging hard X-ray fr-ray observations have highlighted the energetic activity near the Galactic center. The Caltech Gamma-Ray Imaging Payload (GRIP) observed the Galactic center region in 1988 April and again in 1989 April, at energies from 30 keV to 10 MeV. The source 1El740.7-2942 was shown by our measurements, from the 1988 observation, to be the dominant Galactic center source in the energy range 35-200 keV /1/. We present preliminary results on the spectrum of lEl740.7-2942 for the 1989 observation. The question of source variability is of particular interest since lEl 740.7-2942 has been observed to exhibit short term time variability on time scales of days, with the appearance of a hard excess of emission above 200 keV /2/. Recent observations by GRANAT /3/ have shown that the source lEl 7 40. 7-2942 transitioned into an extended "low" state in early 1991.