Peculiar X-ray dips in the superluminal source GRS 1915+105 observed in the soft state

Abstract

This paper reports the detection of a series of X-ray dips in the superluminal black hole source GRS 1915+105 during 1999 June 6-17 from observations carried out with the Pointed Proportional Counters of the Indian X-ray Astronomy Experiment on board the Indian satellite IRS-P3. The observations made in the soft state after the source had made a transition from a low-hard state to a high-soft state, reveal large number of x-ray dips each lasting for about 100- 150 seconds on most of the days. Quasi periodic oscillation (QPOs) with characteristics similar to those of the 0.5-10 Hz QPOs, seen during the low-hard state of the source, were detected in the non-dip portions of the data. The QPOs are, however, not present during the onset or in the dip-period data. During the dips the energy spectrum is soft and the variability is low compared to the non-dip periods. These features re-appear as the dip gradually recovers. Coincident with the occurrence of a large number of X-ray dips, a huge radio flare of strength 0.48 Jy (at 2.25 GHz) was found from the NRAO archival data. It is suggested that the X-ray dips represent mass ejection due to the evacuation of matter from an accretion disk around the black hole and that a super-position of a large number of such dip events leads to production of huge radio jet in GRS 1915+105.