RAPID BURSTS FROM GRS-1915+105 WITH RXTE

The light curves of GRS 1915+105 observed with RXTE on 1996 October 15 reveal a wide range of transient activity, including regular bursts w ith a recurrence time of about 1 minute, irregular bursts, and dips. I n contrast to bursts from other sources, a secondary (and a tertiary) weaker burst immediately following the primary burst are observed. Det ailed energy spectra indicate that the source softens during the main outburst and successively hardens during the secondary and tertiary bu rsts. This may imply that the accretion flow has a corona-disk configu ration and that the relative contribution of the hot corona decreases during the primary bursts and increases during the secondary and terti ary bursts. The primary burst profile resembles the bursts produced in the time-dependent evolutions of accretion disks, which are thermally and viscously unstable. The secondary burst may reflect an inward shi ft of the inner edge of the disk, which results in a greater release o f gravitational binding energy.