Multi-wavelength observations of Galactic hard X-ray sources discovered by INTEGRAL. II. The environment of the companion star

TL;DR

This study investigates the environments of supergiant X-ray binaries discovered by INTEGRAL, focusing on mid-infrared emissions to understand the contribution of companion stars and surrounding material.

Contribution

It provides the first mid-infrared spectral energy distributions of twelve supergiant X-ray binaries, revealing MIR excesses in some and clarifying the nature of their enshrouding material.

Findings

MIR excess detected in IGR J16318-4848, IGR J16358-4726, and possibly IGR J16195-4945.

Most sources do not show MIR excess despite high intrinsic absorption.

The environment around some systems includes enshrouding material contributing to MIR emission.

Abstract

Context: The INTEGRAL mission has led to the discovery of a new type of supergiant X-ray binaries (SGXBs), whose physical properties differ from those of previously known SGXBs. Those sources are in the course of being unveiled by means of multi-wavelength X-rays, optical, near- and mid-infrared observations, and two classes are appearing. The first class consists of obscured persistent SGXBs and the second is populated by the so-called supergiant fast X-ray transients (SFXTs). Aims: We report here mid-infrared (MIR) observations of the companion stars of twelve SGXBs from these two classes in order to assess the contribution of the star and the material enshrouding the system to the total emission.} Methods: We used data from observations we carried out at ESO/VLT with VISIR, as well as archival and published data, to perform broad-band spectral energy distributions of the companion stars and fitted them with a combination of two black bodies representing the star and a MIR excess due to the absorbing material enshrouding the star, if there was any. Results: We detect a MIR excess in the emission of IGR J16318-4848, IGR J16358-4726, and perhaps IGR J16195-4945. The other sources do not exhibit any MIR excess even when the intrinsic absorption is very high. (abridged)