Broadband ESO/VISIR-Spitzer infrared spectroscopy of the obscured supergiant X-ray Binary IGR J16318-4848

TL;DR

This study uses infrared spectroscopy to analyze the environment of the obscured supergiant X-ray binary IGR J16318-4848, revealing dust and gas characteristics and the star's circumstellar structure, advancing understanding of such systems.

Contribution

First infrared spectroscopic analysis of IGR J16318-4848 confirming dust and gas enshrouding the system and characterizing the circumstellar environment.

Findings

Presence of dust and cold gas surrounding the binary system.

The star is surrounded by an irradiated rim and a viscous disk.

Exclusion of spherical dust geometry around the star.

Abstract

A new class of X-ray binaries has been recently discovered by the high energy observatory, INTEGRAL. It is composed of intrinsically obscured supergiant high mass X-ray binaries, unveiled by means of multi-wavelength X-ray, optical, near- and mid-infrared observations, in particular photometric and spectroscopic observations using ESO facilities. However the fundamental questions about these intriguing sources, namely their formation, evolution, and the nature of their environment, are still unsolved. Among them, IGR J16318-4848 - a compact object orbiting around a supergiant B[e] star - seems to be one of the most extraordinary celestial sources of our Galaxy. We present here new ESO/VLT VISIR mid-infrared (MIR) spectroscopic observations of this source. First, line diagnostics allow us to confirm the presence of absorbing material (dust and cold gas) enshrouding the whole binary system, and to characterise the nature of this material. Second, by fitting broadband near to mid-infrared Spectral Energy Distribution - including ESO NTT/SofI, VLT/VISIR and Spitzer data - with a phenomenological model for sgB[e] stars, we show that the star is surrounded by an irradiated rim heated to a temperature of 3800-5500 K, along with a viscous disk component at an inner temperature of 750 K. VISIR data allow us to exclude the spherical geometry for the dust component. This detailed study will allow us in the future to get better constraints on the formation and evolution of such rare and short-living high mass X-ray binary systems in our Galaxy.