MG13 - Talk detail

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Abstract

The galactic black hole GRS 1915+105 exhibits at least seventeen types of variability classes. Transitions from one class to another take place in a matter of hours. Within each class, the spectral state transitions (burst-off to burst-on and vice versa) take place in a matter of few seconds. In the present paper, we show that the class transition could be explained satisfactorily using two component models. We find a dynamical hardness ratio which is obtained from the ratio of the blackbody photon and the power-law photons and call it the Comptonizing efficiency (CE). We see that the average CE in a class is distinct. This means that the so-called `Compton cloud´ changes its optical depth and the accretion rate of the disk, not only while going from one state to another, it also changes its size from one class to another. Around the mean CE of a few classes, there is a scatter of CE which is achieved in timescales of a few to a few tens of seconds. This can be achieved by variation of the ¨local¨ accretion rates of Keplerian and sub-Keplerian flows. When the classes are arranged sequentially and CE vs classes is plotted, a handful of class transitions which have been seen through the IXAE payload appear to correspond to the transition to the nearest neighbour in this plot. Thus, we pin-point two major causes of the variability of the enigmatic black hole candidate GRS 1915+105.

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