X-Ray timing studies of GRS 1915+105

Abstract

The galactic superluminal jet source GRS 1915+105 was observed with the Indian X-ray Astronomy Experiment (IXAE) during 23-27 July, 1996. During our observations the source intensity remained constant within 20% of the daily average. The light curve does not show significant intensity variations at time scale of a minute or more. Instead, we have detected large intensity variations by a factor of 2 to 3 on 100 ms to few seconds time scale in this source. The hardness ratio (6-18 keV to 2-6 keV) appears to be anticorrelated to the short time intensity variations. The quiescent state with about 500 mCrab intensity of this source during our observations is also verified from the ASM (onboard RXTE) light curve. The fine details of timing behavior of this source during the quiescent state will be presented. Strong Quasi Periodic Oscillations (QPO) in the frequency range 0.62 to 0.82 Hz with a narrow peak of width about 0.2 Hz was detected. The short time intensity variations and the nature of the power density spectrum showing QPOs makes the case stronger for this source to be a black hole. These results will be discussed in light of the current models of black hole binaries and are expected to improve our understanding of emission from accretion discs around black hole sources.