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The Extreme Spin of the Black Hole in Cygnus X-1The compact primary in the X-ray binary Cygnus X-1 was the first black hole to be established via dynamical observations. We have recently determined accurate values for its mass and distance, and for the orbital inclination angle of the binary. Building on these results, which are based on our favored (asynchronous) dynamical model, we have measured the radius of the inner edge of the black hole s accretion disk by fitting its thermal continuum spectrum to a fully relativistic model of a thin accretion disk. Assuming that the spin axis of the black hole is aligned with the orbital angular momentum vector, we have determined that Cygnus X-1 contains a near-extreme Kerr black hole with a spin parameter a* > 0.95 (3(sigma)). For a less probable (synchronous) dynamical model, we find a. > 0.92 (3 ). In our analysis, we include the uncertainties in black hole mass, orbital inclination angle, and distance, and we also include the uncertainty in the calibration of the absolute flux via the Crab. These four sources of uncertainty totally dominate the error budget. The uncertainties introduced by the thin-disk model we employ are particularly small in this case given the extreme spin of the black hole and the disk s low luminosity.
Document ID
20120002555
Document Type
Reprint (Version printed in journal)
Authors
Gou, Lijun (Harvard-Smithsonian Center for Astrophysics Cambridge, MA, United States)
McClintock, Jeffrey E. (Harvard-Smithsonian Center for Astrophysics Cambridge, MA, United States)
Reid, Mark J. (Harvard-Smithsonian Center for Astrophysics Cambridge, MA, United States)
Orosz, Jerome A. (San Diego State Univ. San Diego, CA, United States)
Steiner, James F. (Harvard-Smithsonian Center for Astrophysics Cambridge, MA, United States)
Narayan, Ramesh (Harvard-Smithsonian Center for Astrophysics Cambridge, MA, United States)
Xiang, Jingen (Harvard-Smithsonian Center for Astrophysics Cambridge, MA, United States)
Remillard, Ronald A. (Massachusetts Inst. of Tech. Cambridge, MA, United States)
Arnaud, Keith A. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Davis, Shane W. (Canadian Inst. for Theoretical Astrophysics Toronto, Ontario, Canada)
Date Acquired
August 25, 2013
Publication Date
December 1, 2011
Publication Information
Publication: The Astrophysical Journal
Volume: 742
Issue: 2
Subject Category
Astronomy
Report/Patent Number
GSFC.JA.5657.2011
Funding Number(s)
CONTRACT_GRANT: DD1-12054X
CONTRACT_GRANT: DD0-11049X
CONTRACT_GRANT: NNX11AD08G
Distribution Limits
Public
Copyright
Other