Reestimating the Spin Parameter of the Black Hole in Cygnus X1
Abstract
Cygnus X1 is a wellstudied persistent black hole Xray binary. Recently, the three parameters needed to estimate the black hole spin of this system, namely the black hole mass M, the orbital inclination i, and the source distance D, have been updated. In this work we redetermine the spin parameter using the continuumfitting technique for those updated parameter values. 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 the spin estimate arising from the combined observational uncertainties is obtained via Monte Carlo simulations. We demonstrate that, without considering the counteracting torque effect, the new spin parameter is constrained to be a_{*} > 0.9985 (3σ), which confirms that the spin of the black hole in Cygnus X1 is extreme.
 Publication:

The Astrophysical Journal
 Pub Date:
 February 2021
 DOI:
 10.3847/15384357/abbcd6
 arXiv:
 arXiv:2102.09093
 Bibcode:
 2021ApJ...908..117Z
 Keywords:

 Xray binary stars;
 Black hole physics;
 High energy astrophysics;
 1811;
 159;
 739;
 Astrophysics  High Energy Astrophysical Phenomena
 EPrint:
 ApJ published