What Is the Black Hole Spin in Cyg X-1?

Understand

We perform a detailed study of the black hole spin of Cyg X-1, using accurate broad-band X-ray data obtained in the soft spectral state by simultaneous NICER and NuSTAR observations, supplemented at high energies by INTEGRAL data.

• We use the relativistic disk model kerrbb together with different models of the Comptonization high energy tail and the relativistically-broadened reflection features.
• Unlike most previous studies, we tie the spin parameters of the disk and relativistic broadening models, thus combining the continuum and reflection methods of spin determination.
• We also consider a likely increase of the disk color correction due to a partial support of the disk by large scale magnetic fields.