A stochastic propagation model to the energy dependent rapid temporal behaviour of Cygnus X-1 as observed by AstroSat in the hard state. Issue 2 (1st April 2019)

• Record Type: Journal Article
• Authors: Maqbool, Bari; Mudambi, Sneha Prakash; Misra, R; Yadav, J S; Gudennavar, S B; Bubbly, S G; Rao, A; Jogadand, S; Patil, M K; Bhattacharyya, S; Singh, K P
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 486:Issue 2(2019)
• Page Start: 2964
• Page End: 2975
• Publication Date: 2019-04-01
• Subjects: accretion, accretion discs -- black hole physics -- X-rays: binaries -- X-rays: individual: Cygnus X-1; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stz930
• Languages: English
• ISSNs: 0035-8711

Abstract

Abstract: We report the results from analysis of six observations of Cygnus X-1 by Large Area X-ray Proportional Counter (LAXPC) and Soft X-ray Telescope (SXT) onboard 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 disc 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 disc with a hot inner region. Unlike other propagation models, the hard X-ray emission (>4 keV) is assumed to be from the hot inner disc by a single-temperature thermal Comptonization process. The fluctuations first cause a variation in the temperature of the truncated disc and then the temperature of the inner disc after a frequency dependent time delay. We find that the model can explain the energy dependent rms and time-lag at different frequencies.