Re-estimating the Spin Parameter of the Black Hole in Cygnus X-1

Cygnus X-1 is a well-studied persistent black hole X-ray binary. Recently, the three parameters needed to estimate spin of this system, namely mass $M$, orbital inclination $i$ and source distance $D$, have been updated. In work we redetermine parameter using continuum-fitting technique for those updated values. Based on assumption that axis aligned with plane, fit thermal disk component fully relativistic thin accretion model. The error in arising from combined observational uncertainties obtained via Monte Carlo (MC) simulations. We demonstrate that, without considering counteracting torque effect, new constrained be a$_* > 0.9985$ (3$\sigma$), which confirms extreme.