Spin and Accretion Rate Dependence of Black Hole X-Ray Spectra

TL;DR

This study investigates how black hole X-ray spectra depend on parameters like spin, accretion rate, and composition, revealing key spectral feature variations and higher efficiencies than classical models predict.

Contribution

It provides a first-principles analysis of spectral feature dependencies on physical parameters, highlighting the greater radiative efficiency and the dominant influence of accretion rate over spin.

Findings

Power law component hardens with increasing spin.

Thermal component strengthens with higher accretion rate.

Fe Kα equivalent width grows sub-linearly with Fe abundance.

Abstract

We present a survey of how the spectral features of black hole X-ray binary systems depend on spin, accretion rate, viewing angle, and Fe abundance when predicted on the basis of first principles physical calculations. The power law component hardens with increasing spin. The thermal component strengthens with increasing accretion rate. The Compton bump is enhanced by higher accretion rate and lower spin. The Fe K$\alpha$ equivalent width grows sub-linearly with Fe abundance. Strikingly, the K$\alpha$ profile is more sensitive to accretion rate than to spin because its radial surface brightness profile is relatively flat, and higher accretion rate extends the production region to smaller radii. The overall radiative efficiency is at least 30--100% greater than as predicted by the Novikov-Thorne model.