Description
Cygnus X-1 is a well-studied persistent black hole X-ray binary. Recently, three dynamical parameters of this system, namely the black hole mass M, the orbital inclination i and the source distance D, have been updated. This present work attempts to refine the spin of the black hole with these new parameters. The continuum- fitting technique is adopted in this work. Based on the assumption that the spin axis of the black hole is aligned with the orbital plane, we fit the thermal disk component to a fully relativistic thin accretion disk model. The error in spin from the combined observational uncertainties is obtained via Monte Carlo (MC) simulations. We demonstrate that the new spin parameter is constrained to be a∗ > 0.9985 (3σ), which confirms that the spin of the black hole in Cygnus X-1 is extreme.
