AstroSat/LAXPC Observation of Cygnus X-1 in the Hard State

作者：Misra Ranjeev; Yadav J S; Chauhan Jai Verdhan; Agrawal P C; Antia H M; Pahari Mayukh; Chitnis V R; Dedhia Dhiraj; Katoch Tilak; Madhwani P; Manchanda R K; Paul B; Shah Parag

来源：Astrophysical Journal, 2017, 835(2): 195.

DOI：10.3847/1538-4357/835/2/195

• accretion, accretion disks
• black hole physics
• X-rays: binaries
• X-rays: individual (Cyg X-1)

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 similar to 1.8 and high temperature of kT(e) > 60 keV along with weak reflection and possible disk emission. The power spectrum can be characterized by two broad lorentzian functions centered at similar to 0.4 and similar to 3 Hz. The rms of the low-frequency component decreases from similar to 15% at around 4 keV to similar to 10% at around 50 keV, while that of the high-frequency one varies less rapidly from similar to 13.5% to similar 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 similar to 50 milliseconds from 0.3 to 0.9 Hz, decreasing to similar to 8 milliseconds from 2 to 5 Hz and finally dropping to similar 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 similar to 1.72 to similar 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.

• 出版日期2017-2-1