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 satellite IRS-P3. The observations were made after the source made a transition from a steady low-hard state to a chaotic state which occuered within a few hours. Dips of about 20−160 seconds duration are observed on most of the days. The X-ray emission outside the dips shows a QPO at ∼4 Hz which 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 non-dip periods. These features gradually re-appear 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 super-position of a large number of such dip events produces a huge radio jet in GRS 1915+105.

Ejection of the inner accretion disk in GRS 1915+105: The magnetic rubber-band effect

“…These dips are also seen in class θ light curves. During a major portion of the huge radio flares associated with superluminal blob emission a series of soft dips are present (Naik et al 2001). Mirabel & Rodriguez (1999) have pointed out that in each epoch of this type of outflow, the mass condensation is around 10 23 g. In order to achieve this, we require that matter is accumulated from disk evacuation at each "dip" and within each epoch, successive mini-blobs move faster than the earlier blob in order to "catch up".…”

“…This may indicate some other runaway process with a longer time scale of tens of days. Naik et al (2001) have observed such X-ray dips at a rate of once in a few hundred seconds during the peak or the radio flare. If there are ∼1000 evacuation events during an episode of superluminal blob ejection (in a few days), then total mass condensation would be 10 23 g. Hence in order to explain the observation of Mirabel & Rodriguez (1999), one must require that in each epoch, matter is accumulated from at least a thousand evacuation events.…”

“…These outflows, however, are confined to the sonic sphere and fall back on the accretion disk after being cooled down by an inverse Compton effect. It was pointed out by Naik & Rao (2001) that the source does not show appreciable radio emission during such oscillations. A detailed inflow/outflow model has not been presented for this source to explain the radio emission, particularly to explain the superluminally moving radio blobs.…”

“…are observed in this source. Several attempts have been made to associate the radio emission, presumably coming from jets, to the X-ray emission from the accretion disks (Fender et al 1999;Naik et al 2001;Naik & Rao 2001). The Spectral signature of winds from the Comptonising region has also been identified ).…”

“…Recently Naik et al (2001) have detected a series of soft X-ray dips during the declining phase of a huge radio flare and have postulated that such soft dips are responsible for the jet emission. Vadawale et al (2001) made a detailed study of X-ray dips observed during the radio flare using the Rossi X-ray Timing Experiment (RXTE) data and have presented evidence for the disappearance of the inner accretion disk during the dips.…”