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Title: Confirmation via the continuum-fitting method that the spin of the black hole in Cygnus X-1 is extreme

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 holemore » is a{sub *} > 0.983 (3σ).« less
Authors:
 [1] ; ; ; ; ;  [2] ;  [3] ;  [4] ;  [5]
  1. National Astronomical Observatory, Chinese Academy of Science, Beijing 100012 (China)
  2. Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)
  3. Kavli Institute for Astrophysics and Space Research, MIT, 70 Vassar Street, Cambridge, MA 02139 (United States)
  4. Department of Astronomy, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182 (United States)
  5. Remeis-Observatory and ECAP, University of Erlangen-Nuremberg, Sternwartstrasse 7, D-96049 Bamberg (Germany)
Publication Date:
OSTI Identifier:
22365603
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 790; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BINARY STARS; BLACK HOLES; COMPTON EFFECT; KERR FIELD; PHOTONS; SPECTRA; SPIN; X RADIATION