Title:	AstroSat/LAXPC Observation of Cygnus X-1 in the Hard State.
Authors:	Misra, Ranjeev Yadav, J.S. Paul, Biswajit +10 Co-authors
Issue Date:	Feb-2017
Publisher:	IOP Sciences for The American Astronomical Society
Citation:	Astrophysical Journal, 2017, Vol. 835, p 195
Abstract:	We report the first analysis of data from AstroSat/LAXPC observations of Cygnus X-1 in 2016 January. LAXPC spectra reveals that the source was in the canonical hard state, represented by a prominent thermal Comptonization component having a photon index of ~1.8 and high temperature of kTe > 60 keV along with weak reflection and possible disk emission. The power spectrum can be characterized by two broad lorentzian functions centered at ~0.4 and ~3 Hz. The rms of the low-frequency component decreases from ~15% at around 4 keV to ~10% at around 50 keV, while that of the high-frequency one varies less rapidly from ~13.5% to ~11.5% in the same energy range. The time lag between the hard (20–40 keV) and soft (5–10 keV) bands varies in a step-like manner being nearly constant at ~50 milliseconds from 0.3 to 0.9 Hz, decreasing to ~8 milliseconds from 2 to 5 Hz and finally dropping to ~2 milliseconds for higher frequencies. The time lags increase with energy for both the low and high-frequency components. The event mode LAXPC data allows for flux resolved spectral analysis on a timescale of 1 s, which clearly shows that the photon index increased from ~1.72 to ~1.80 as the flux increased by nearly a factor of two. We discuss the results in the framework of the fluctuation propagation model.
Description:	Open Access
URI:	http://hdl.handle.net/2289/6691
ISSN:	0004-637X 1538-4357-(Online)
Alternative Location:	http://adsabs.harvard.edu/abs/2017ApJ...835..195M https://arxiv.org/abs/1612.08793 http://dx.doi.org/ 10.3847/1538-4357/835/2/195
Copyright:	2017, The American Astronomical Society.
Appears in Collections:	Research Papers (A&A)

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