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.