Dynamical Evidence for a Black Hole in GX 339−4

Abstract

The Galactic Low Mass X-ray Binary GX339-4 was one of the earliestproposed black hole candidates, yet even its most fundamental binaryparameters have eluded us for several decades. We present new outburstspectroscopy of GX339-4 which appears to at last reveal the motion ofits elusive companion star in fluorescent NIII lines. Based on ourmulti-site, multi-epoch dataset we propose a new orbital period of 1.7days and hence derive a mass function for the compact object of 5.8Msun, suggesting that it is indeed a black hole. In contrast to themoving NIII lines, the wings of HeII are almost stationary, indicatingan extreme mass ratio and hence further supporting the identification ofthe compact object as a black hole. Besides revealing these fundamentalparameters, the rich and variable emission line spectrum contains muchfurther information allowing us to dissect the X-ray irradiatedaccretion structures in this object. We will discuss what we can learnfrom these data using emission line lightcurves and Doppler tomogramsand compare with theoretical expectations and results from similarsystems containing accreting neutron stars.