On the determination of the spin of the black hole in Cyg X-1 from X-ray reflection spectra

Authors

A. C. Fabian, Institute of Astronomy, Cambridge
D. R. Wilkins, Institute of Astronomy, Cambridge
J. M. Miller, University of Michigan
R. C. Reis, University of Michigan
C. S. Reynolds, University of Maryland
E. M. Cackett, Institute of Astronomy, CambridgeFollow
M. A. Nowak, Kavli Institute for Astrophysics and Space Research, MIT
G. G. Pooley, Cavendish Laboratory, University of Cambridge
K. Pottschmidt, CRESST and NASA Goddard Space Flight Center
J. S. Sanders, Institute of Astronomy, Cambridge
R. R. Ross, College of the Holy Cross
J. Wilms, Dr Karl-Remeis-Sternwarte and Erlangen Center for Astroparticle Physics

Document Type

Article

Abstract

The spin of Cygnus X-1 is measured by fitting reflection models to Suzaku data covering the energy band 0.9-400 keV. The inner radius of the accretion disc is found to lie within 2 gravitational radii (r_g=GM/c²), and a value of ? is obtained for the dimensionless black hole spin. This agrees with recent measurements using the continuum fitting method by Gou et al. and of the broad iron line by Duro et al. The disc inclination is measured at ?, which is consistent with the recent optical measurement of the binary system inclination by Orosz et al. of 27°± 0?8. We pay special attention to the emissivity profile caused by irradiation of the inner disc by the hard power-law source. The X-ray observations and simulations show that the index q of that profile deviates from the commonly used, Newtonian, value of 3 within 3r_g, steepening considerably within 2r_g, as expected in the strong gravity regime.

Disciplines

Cosmology, Relativity, and Gravity | Stars, Interstellar Medium and the Galaxy

Comments

NOTICE IN COMPLIANCE WITH PUBLISHER POLICY: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©2012 The Authors. Published by Oxford University Press on behalf of The Royal Astronomical Society. All rights reserved. Available at doi:10.1111/j.1365-2966.2012.21185.x

Recommended Citation

Fabian, A. C., Wilkins, D. R., Miller, J. M., Reis, R. C., Reynolds, C. S., Cackett, E. M., Nowak, M. A., Pooley, G. G., Pottschmidt, K., Sanders, J. S., Ross, R. R., Wilms, J. 2012. On the determination of the spin of the black hole in Cyg X-1 from X-ray reflection spectra. MNRAS 424(1), 217-223.