Detection of a series of X-ray dips associated with a radio flare in GRS 1915+105

Abstract

We report the detection of a series of X-ray dips in the Galactic black hole candidate 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 Remote Sensing Satellite (IRS-P3). The observations were made after the source made a transition from a steady low-hard state to a chaotic state, which occurred within a few hours. Dips of about 20-160 s in duration were observed on most of the days. The X-ray emission outside the dips shows a quasi-periodic oscillation (QPO) at ~4 Hz that has characteristics similar to the ubiquitous 0.5-10 Hz QPO seen during the low-hard state of the source. During the onset of dips this QPO is absent, and, also, the energy spectrum is soft and the variability is low compared to the nondip periods. These features gradually reappear as the dip recovers. The onset of the occurrence of a large number of such dips followed the start of a huge radio flare of strength 0.48 Jy (at 2.25 GHz). We interpret these dips as the cause for mass ejection due to the evacuation of matter from an accretion disk around the black hole. We propose that a superposition of a large number of such dip events produces a huge radio jet in GRS 1915+105.