Probing the shot behaviour in Cygnus X-1 using simultaneous AstroSat-NICER observation. Issue 4 (28th March 2022)

• Record Type: Journal Article
• Authors: Bhargava, Yash; Hazra, Nandini; Rao, A R; Misra, Ranjeev; Bhattacharya, Dipankar; Roy, Jayashree; Alam, Md Shah
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 512:Issue 4(2022)
• Page Start: 6067
• Page End: 6077
• Publication Date: 2022-03-28
• Subjects: accretion, accretion discs -- X-rays: binaries -- X-rays: general -- X-rays: individual: Cyg X-1 -- X-rays: stars; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stac853
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: We analyse the aperiodic flaring features, also known as shots, observed in Cyg X-1 in the 0.1–80 keV energy band using a 6.39 ks simultaneous observation with AstroSat and Neutron star Interior Composition ExploreR ( NICER ). We detect 49 simultaneous shots in the soft and hard X-ray bands with NICER and AstroSat -LAXPC, respectively. We observe the shot profile for the first time in soft X-rays (0.1–3 keV), which shows a spectral peak at ∼2 keV. Using time-averaged spectroscopy, we measured the truncation of the inner accretion disc at 6.7 ± 0.2 gravitational radii. The shot-phase-resolved spectroscopy allowed us to identify the origin of some of the brightest aperiodic peaks in the soft X-rays. We find that the accretion rate is consistent with a constant during the shots while the inner edge of the accretion disc moves inwards/outwards as these shots rise/decay. We discuss the possible mechanisms causing the swing in the inner radius.