The Spin of the Black Hole GRS 1716-249 Determined from the Hard Intermediate State

Abstract

Abstract We present three simultaneous/quasi-simultaneous NuSTAR and Swift data sets of the black hole (BH) GRS 1716-249 in its hard intermediate state. The accretion disk in this state may have reached the innermost stable circular orbit, and the NuSTAR spectra show a broad relativistic iron line and a strong Compton hump. To measure the BH spin, we construct a joint model consisting of a relativistic disk model kerrbb and a reflection model relxill, to fit the continuum and the reflection components, respectively. By applying this model to each data set independently, a consistent result is obtained on the BH spin and the disk inclination. The BH spin is a* ≳ 0.92, and the inclination angle (i) is around 40°–50°, based on the measurements of all data sets. In the third data set, a high BH mass (M BH) is strongly disfavored by the spectral fits. By unfreezing the BH mass, we find a* > 0.92, , and M BH < 8.0 M ⊙, at a 90% confidence level. Considering the lower limit derived from a previous optical constraint, M BH is in a range of 4.9–8.0 M ⊙.