Confirmation via the continuum-fitting method that the spin of the black hole in Cygnus X-1 is extreme
- National Astronomical Observatory, Chinese Academy of Science, Beijing 100012 (China)
- Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)
- Kavli Institute for Astrophysics and Space Research, MIT, 70 Vassar Street, Cambridge, MA 02139 (United States)
- Department of Astronomy, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182 (United States)
- Remeis-Observatory and ECAP, University of Erlangen-Nuremberg, Sternwartstrasse 7, D-96049 Bamberg (Germany)
In Gou et al., we reported that the black hole primary in the X-ray binary Cygnus X-1 is a near-extreme Kerr black hole with a spin parameter a{sub *} > 0.95 (3σ). We confirm this result while setting a new and more stringent limit: a{sub *} > 0.983 at the 3σ (99.7%) confidence level. The earlier work, which was based on an analysis of all three useful spectra that were then available, was possibly biased by the presence in these spectra of a relatively strong Compton power-law component: the fraction of the thermal seed photons scattered into the power law was f{sub s} = 23%-31%, while the upper limit for reliable application of the continuum-fitting method is f{sub s} ≲ 25%. We have subsequently obtained six additional spectra of Cygnus X-1 suitable for the measurement of spin. Five of these spectra are of high quality with f{sub s} in the range 10%-19%, a regime where the continuum-fitting method has been shown to deliver reliable results. Individually, the six spectra give lower limits on the spin parameter that range from a{sub *} > 0.95 to a{sub *} > 0.98, allowing us to conservatively conclude that the spin of the black hole is a{sub *} > 0.983 (3σ).
- OSTI ID:
- 22365603
- Journal Information:
- Astrophysical Journal, Vol. 790, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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