Rapid Bursts From GRS 1915+105 with RXTE

The light curves of GRS 1915+105 observed with RXTE on October 15, 1996 reveal a wide range of transient activity including regular bursts with a recurrence time of about 1 minute, irregular bursts, and dips. In contrast to bursts from other sources, a secondary (and a tertiary) weaker burst immediately following the primary burst are observed. Detailed energy spectra indicate that the source softens during the main outburst and successively hardens during the secondary and tertiary bursts. This may imply that the accretion flow has a corona-disk configuration and that the relative contribution of the hot corona decreases during the primary bursts and increases during the secondary and tertiary 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 shift of the inner edge of the disk which results in a greater release of gravitational binding energy.