EGRET UPPER LIMITS ON THE HIGH-ENERGY GAMMA-RAY EMISSION OF X-RAY NOVAE

摘要

We report EGRET upper limits on the high-energy γ-ray emission of three X-ray novae: 4U 1543-47, GRO J0422+32, and GRO J1655-40. The implications of these upper limits are discussed. GRO J1655-40 is of particular interest because it has been identified as a superluminal radio source. Unfortunately, the radio flux was low during the EGRET observation. If the jet power inferred from the peak of the radio emission existed at the time of the EGRET observation, our EGRET upper limit implies that the fraction of jet power emitted as EGRET γ-rays is less than 12%. We speculate upon the origin of the radio emission, and discuss the implications for the production efficiency of GeV γ-rays.