Initial Measurements of Black Hole Spin in GX 339-4 from Suzaku Spectroscopy

TL;DR

This study uses Suzaku X-ray observations to measure the spin of the stellar-mass black hole GX 339-4, finding a high spin value around 0.93, marking one of the first direct measurements of black hole spin via relativistic line modeling.

Contribution

It introduces a new relativistic line function for spin measurement and demonstrates consistent spin estimates across different observations, advancing black hole spin measurement techniques.

Findings

Black hole spin measured as a = 0.93 +/- 0.01

Relativistic line modeling provides consistent spin estimates

Disk reflection models are robust against scattering effects

Abstract

We report on a deep Suzaku observation of the stellar-mass black hole GX 339-4 in outburst. A clear, strong, relativistically-shaped iron emission line from the inner accretion disk is observed. The broad-band disk reflection spectrum revealed is one of the most sensitive yet obtained from an accreting black hole. We fit the Suzaku spectra with a physically-motivated disk reflection model, blurred by a new relativistic line function in which the black hole spin parameter is a variable. This procedure yielded a black hole spin parameter of a = 0.89 +/- 0.04. Joint modeling of these Suzaku spectra and prior XMM-Newton spectra obtained in two different outburst phases yields a spin parameter of a = 0.93 +/- 0.01. The degree of consistency between these results suggests that disk reflection models allow for spin measurements that are not strongly biased by scattering effects. We suggest that the best value of the black hole spin parameter is a = 0.93 +/- 0.01 (statistical) +/- 0.04 (systematic). Although preliminary, these results represent the first direct measurement of non-zero spin in a stellar-mass black hole using relativistic line modeling.