The spatial distribution of circumstellar material of the wind-fed system GX 301-2

TL;DR

This study measures the size and distribution of Fe Kα-emitting material around GX 301-2, revealing a larger-than-expected region influenced by tidal streams, and highlights the unsteady nature of accretion in supergiant X-ray binaries.

Contribution

First detailed measurement of the spatial distribution of Fe Kα emission in GX 301-2 using time delay analysis, suggesting tidal streams dominate mass loss.

Findings

Fe Kα-emitting region size is 40 ± 20 light-seconds.

Region size exceeds accretion radius from stellar wind.

Unsteady accretion flow evidenced by different delays during quiescent and flare periods.

Abstract

The distribution of the circumstellar material in systems of supergiant X-ray binaries (SgXBs) is complex and not well probed observationally. We report a detailed study of the spatial distribution of the Fe K{\alpha}-emitting material in the wind-fed system GX 301-2, by measuring the time delay between the Fe K{\alpha} line and the hard X-ray continuum (7.8-12 keV) using the cross-correlation method, based on XMM-Newton observation. We found that to obtain the true time delay, it is crucial to subtract the underlying continuum of the Fe K{\alpha} line. The measured size of the Fe K{\alpha}-emitting region over the whole observation period is 40 {\pm} 20 light-seconds. It is 5 times larger than the accretion radius estimated from a quasi-isotropic stellar wind, but consistent with the one estimated from a tidal stream, which could be the dominant mass-loss mechanism of GX 301-2 as inferred from the orbital distribution of the absorption column density previously. The measured time delay of the quiescent period is a little smaller than those of the flare periods, revealing the unsteady behaviour of the accretion flow in GX 301-2. Statistical and detailed temporal studies of the circumstellar material in SgXBs are expected for a large sample of SgXBs with future X-ray missions, such as Athena and eXTP.