A stochastic propagation model to the energy dependent rapid temporal behaviour of Cygnus X-1 as observed by AstroSat in the hard state. (arXiv:1904.01598v1 [astro-ph.HE])

A stochastic propagation model to the energy dependent rapid temporal behaviour of Cygnus X-1 as observed by AstroSat in the hard state. (arXiv:1904.01598v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Maqbool_B/0/1/0/all/0/1">Bari Maqbool</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Prakash_M/0/1/0/all/0/1">M. Sneha Prakash</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Misra_R/0/1/0/all/0/1">R. Misra</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Yadav_J/0/1/0/all/0/1">J. S. Yadav</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gudennavar_S/0/1/0/all/0/1">S. B. Gudennavar</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bubbly_S/0/1/0/all/0/1">S. G. Bubbly</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Rao_A/0/1/0/all/0/1">A. Rao</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Jogadand_S/0/1/0/all/0/1">S. Jogadand</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Patil_M/0/1/0/all/0/1">M. K. Patil</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bhattacharyya_S/0/1/0/all/0/1">S. Bhattacharyya</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Singh_K/0/1/0/all/0/1">K. P. Singh</a>

We report the results from analysis of six observations of Cygnus X-1 by
Large Area X-ray Proportional Counters (LAXPC) and Soft X-ray Telescope (SXT)
on-board AstroSat, when the source was in the hard spectral state as revealed
by the broad band spectra. The spectra obtained from all the observations can
be described by a single temperature Comptonizing region with disk and
reflection components. The event mode data from LAXPC provides unprecedented
energy dependent fractional root mean square (rms) and time-lag at different
frequencies which we fit with empirical functions. We invoke a fluctuation
propagation model for a simple geometry of a truncated disk with a hot inner
region. Unlike other propagation models, the hard X-ray emission (> 4 keV) is
assumed to be from the hot inner disk by a single temperature thermal
Comptonization process. The fluctuations first cause a variation in the
temperature of the truncated disk and then the temperature of the inner disk
after a frequency dependent time delay. We find that the model can explain the
energy dependent rms and time-lag at different frequencies.

We report the results from analysis of six observations of Cygnus X-1 by
Large Area X-ray Proportional Counters (LAXPC) and Soft X-ray Telescope (SXT)
on-board AstroSat, when the source was in the hard spectral state as revealed
by the broad band spectra. The spectra obtained from all the observations can
be described by a single temperature Comptonizing region with disk and
reflection components. The event mode data from LAXPC provides unprecedented
energy dependent fractional root mean square (rms) and time-lag at different
frequencies which we fit with empirical functions. We invoke a fluctuation
propagation model for a simple geometry of a truncated disk with a hot inner
region. Unlike other propagation models, the hard X-ray emission (> 4 keV) is
assumed to be from the hot inner disk by a single temperature thermal
Comptonization process. The fluctuations first cause a variation in the
temperature of the truncated disk and then the temperature of the inner disk
after a frequency dependent time delay. We find that the model can explain the
energy dependent rms and time-lag at different frequencies.

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