Spectral characteristics of the black hole binary 4U 1957+115: a multi mission perspective

ABSTRACT We report spectral analysis of the persistent black hole X-ray binary, 4U 1957+115, using AstroSat, Swift, and NuSTAR observations carried out between 2016 2019. Modelling with a disc emission, thermal Comptonization, blurred reflection components revealed that source was in high-soft state flux ∼87 per cent total high-energy photon index ∼2.6. There is an evidence either inner radius varied by ∼25 or colour hardening factor changed ∼12 cent. The values imply for non-spinning hole, mass < 7 M ⊙ located > 30 kpc away. On other hand, rapidly spinning would be consistent more plausible 10 distance ∼10 kpc. Fixing to relativistic accretion model, constrained 6 M⊙ inclination angle 72°. A positive correlation detected rate radii equivalently factor.