Different types of X-ray bursts during high state of the superluminal source GRS 1915+105

Abstract

We have observed the galactic superluminal X-ray transient source GRS 1915+105 in its high state from June 12 to August 10, 1997 with the pointed proportional counters (PPCs) of Indian X-ray Astronomy Experiment on board IRS-P3 satellite. The observed light curves have revealed the presence of four types of intense X-ray bursts: regular persistent bursts with two distinct time scales, quasi-regular bursts and irregular bursts. These bursts have unique characteristics of slow exponential rise and fast linear decay and are different from the classical bursts seen in Low Mass X-ray Binaries. GRS 1915+105 is the only black hole source in which such X-ray bursts are observed. During this period, the total 2–18 keV flux changed by a factor of 3 and quiescent time hardness ratio remained in the region 0.9-1.4. We discuss our results in the light of recent results from RXTE/PCA of other galactic superluminal source GRO J1655-40 during its high state and speculate why such bursts have not been observed so far from GRO J1655-40.