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Session 48 - Gamma Rays & X-ray Instrumentation.
Display session, Thursday, January 08
We show that: 1) The Fourier frequency-dependent hard X-ray lag, first discovered from the analysis of aperiodic variability of the light curves of the black hole candidate Cygnus X-1, is a fairly common phenomenon among accreting compact sources. 2) The hard X-ray time lag can be explained in terms of Comptonization process in non-uniform and extended coronae of hot electrons. 3) The density profile of a corona can significantly affect the Comptonization energy spectrum from it. Consequently, fitting the energy spectrum alone is not sufficient to uniquely determine the optical depth and temperature of the Comptonization cloud if its density profile is unknown. 4) The time lag as a function of Fourier frequency for the X-rays in two energy bands is sensitive to the density distribution of the scattering corona. Thus simultaneous analysis of the spectral and temporal X-ray data will allow us to probe the density structure of the Comptonizing corona and thereby the dynamics of mass accretion onto the compact object.
Program listing for Thursday