Probing the inner region of Cygnus X-1 in the low/hard state through its x-ray broadband spectrum

Di Salvo, T.; Done, C.; Życki, P.T.; Burderi, L.; Robba, N.R.

Abstract

We present the broadband X-ray spectrum of Cyg X-1 in the low/hard state as observed by the instruments on board BeppoSAX. The spectrum spans from 0.1 to 200 keV, allowing the total accretion luminosity to be observed rather than extrapolated, corresponding to 2% of the Eddington limit for a 10 M black hole. The broad bandpass allows us to determine the continuum shape with great accuracy. Simple models of Compton upscattering of seed photons from the accretion disk do not adequately match the spectrum. At low energies an additional continuum component is required, giving a complex soft excess which extends up to 4 keV, in line with previous results from ASCA. Moreover, we clearly detect a reflected component from the accretion disk that is smeared, probably because of relativistic and Doppler effects. The reflecting material is not strongly ionized and does not subtend a large solid angle as seen from the corona (/20.10.3). The estimated inner radius of the disk, which depends on the inclination of the system, is most probably between 10 and 70 gravitational radii (Rg). An unsmeared reprocessed component, probably originating from the companion star or the outer disk, could also be present. In this case, the inner radius of the disk, as inferred from the smeared reflection, is smaller, between 6Rg and 20Rg.

Citation

Di Salvo, T., Done, C., Życki, P., Burderi, L., & Robba, N. (2001). Probing the inner region of Cygnus X-1 in the low/hard state through its x-ray broadband spectrum. Astrophysical Journal, 547(2), 1024-1033. https://doi.org/10.1086/318396

• Journal Article Type: Article
• Publication Date: 2001-02
• Deposit Date: May 20, 2008
• Publicly Available Date: Aug 12, 2014
• Journal: Astrophysical Journal
• Print ISSN: 0004-637X
• Electronic ISSN: 1538-4357
• Publisher: American Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 547
• Issue: 2
• Pages: 1024-1033
• DOI: https://doi.org/10.1086/318396
• Keywords: Accretion, Accretion Disks, Black Hole Physics, Stars: Individual: Constellation Name: Cygnus X-1, X-Rays: General, X-Rays: Stars
• Public URL: https://durham-repository.worktribe.com/output/1595126