The Spin and Orientation of the Black Hole in XTE J1908$+$094

Abstract

NuSTAR observed the black hole candidate XTE J1908+094 during its 2013 and 2019 outbursts. We use relativistic reflection to measure the spin of the black hole through 19 different assumptions of relxill flavors and parameter combinations. The most favored model in terms of Deviance Information Criterion (DIC) measures the spin of the black hole to be a = 0.55 +0.29 −0.45 , and an inclination of θ = 27 +2 −3 degrees (1σ statistical errors). We look at the effects of coronal geometry assumptions and density of the accretion disk on the spin prediction. All 19 tested models provide consistent spin estimates. We discuss the evolution of spin measurement techniques using relativistic reflection in X-ray binaries and discuss the implications of this spin measurement in reconciling the distributions of stellar mass black hole spin measurements made through X-ray and gravitational wave observations.

Frontiers in accretion physics at high X-ray spectral resolution

“…It has also been postulated that it is not the inner disc, but rather the characteristic scale height of the corona, that instead varies with accretion rate [109]. The line strength depends upon the disc inclination angle, and there remain disagreements between the inferred inner disc inclination (as measured in X-rays) vs. the binary orbital plane (as inferred in the optical) [110,111]. This may point to warped inner disc geometries, which would then need to be accounted for self-consistently when inferring 𝑎 [112].…”