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L.G. Titarchuk (George Mason University/CEOSR), P. Laurent (CEA, DSM/DAPNIA/SAp, Centre d'Etudes de Saclay)
We present the timing and spectral analysis of Monte Carlo simulations of X-ray radiation for a converging inflow (CI) onto a black hole. We demonstrate that a X-ray spectrum of a converging inflow (CI) onto a black hole is the sum of a thermal (disk) component and the convolution of some fraction of this component with the Comptonization spread (Green's) function. The latter component is seen as an extended power law at energies much higher than the characteristic energy of the soft photons. We show that the high energy photon production (source function) in the CI atmosphere is distributed with the characteristic maximum at about the photon bending radius, 1.5rS, independently of the seed (soft) photon distribution. We show that high frequency oscillations of the soft photon source in this region lead to the oscillations of the high energy part of the spectrum but not of the thermal component. Because the effective area of the X-ray emitting disk (\approx 100-120 Schwarzschild square radii) is one order of magnitude larger than that of the inner edge region which is of order of \approx(9-10) rS2. The high frequency oscillations of the inner region are not significant in the thermal component of the spectrum. We further demonstrate that Doppler and recoil effects (which are responsible for the formation of the CI spectrum) are related to the hard (positive) and soft (negative) time lags between the soft and hard photon energy channels respectively. We demonstrate the presence of two types of time lags in the simulated CI spectra. We conclude that the high frequency QPO is related to the extended power law spectral component, the soft and hard time lags are inevitable and natural properties of the X-ray emission from the converging inflows onto black holes.
The author(s) of this abstract have provided an email address for comments about the abstract: lev@xip.nrl.navy.mil