A systematic look at the Very High and Low/Hard state of GX 339-4: Constraining the black hole spin with a new reflection model

TL;DR

This study analyzes GX 339-4's extreme states using simultaneous XMM-Newton and RXTE observations, employing a new reflection model to accurately measure the black hole's high spin parameter.

Contribution

It introduces a self-consistent reflection model that includes disc blackbody radiation and Comptonisation, enabling precise black hole spin measurement from spectral data.

Findings

Black hole spin of GX 339-4 is approximately 0.935.

Both states show an ionised thin accretion disc reaching the innermost stable orbit.

The reflection signatures are consistent across different spectral states.

Abstract

We present a systematic study of GX 339-4 in both its very high and low hard states from simultaneous observations made with XMM-Newton and RXTE in 2002 and 2004. The X-ray spectra of both these extreme states exhibit strong reflection signatures, with a broad, skewed Fe-Kalpha line clearly visible above the continuum. Using a newly developed, self-consistent reflection model which implicitly includes the blackbody radiation of the disc as well as the effect of Comptonisation, blurred with a relativistic line function, we were able to infer the spin parameter of GX 339-4 to be 0.935 +/- 0.01 (statistical) +/- 0.01 (systematic) at 90 per cent confidence. We find that both states are consistent with an ionised thin accretion disc extending to the innermost stable circular orbit around the rapidly spinning black hole.