Evidence for Postquiescent, High-Energy Emission from Gamma-Ray Burst 990104

It is well known that high-energy emission (MeV-GeV) has been observed in anumber of gamma-ray bursts, and temporally-extended emission from lower energygamma rays through radio wavelengths is well established. An important observedcharacteristic of some bursts at low energy is quiescence: an initial emissionfollowed by a quiet period before a second (postquiescent) emission. Evidencefor significant high-energy, postquiescent emission has been lacking. Here wepresent evidence for high-energy emission, coincident with lower energyemission, from the postquiescent emission episode of the very bright and longburst, GRB 990104. We show light curves and spectra that confirm emission above50 MeV, approximately 152 seconds after the BATSE trigger and initial emissionepisode. Between the initial emission episode and the main peak, seen at bothlow and high energy, there was a quiescent period of ~100 s during which theburst was relatively quiet. This burst was found as part of an ongoing searchfor high-energy emission in gamma-ray bursts using the EGRET fixed interval (32s) accumulation spectra, which provide sensitivity to later, high-energyemission that is otherwise missed by the standard EGRET BATSE-triggered burstspectra.Comment: 5 pages, including 5 figures. Missing citation added to introduction. Accepted for publication in ApJ