Highly obscured IGR sources
INTEGRAL has revealed a newly-discovered population of highly obscured X-ray binary systems. To better understand this emerging population, Sylvain Chaty and collaborators have selected a sample of INTEGRAL (IGR) sources for which an accurate localisation was available. This image shows nine of the thirteen sources studied by Sylvain Chaty et al. The aim of the study was to identify the stellar counterpart and to reveal the nature of the companion star and of the binary system (see related publications).
A multi-wavelength optical to NIR study using the European Southern Observatory (ESO) New Technology Telescope (NTT) was performed in order to perform accurate astrometry (shown in this Figure), photometry and spectroscopy of various candidate counterparts.
The above image is Figure 2 from Chaty, S. et al. , showing finding charts of nine of the thirteen INTEGRAL sources, observed at the ESO NTT telescope in the infrared KS band (2.2 μm). Fields of view: 1'x1'. North is to the top and East to the left. Overplotted are the most accurate localisations available to date.
In addition to the ESO NTT optical and NIR observations, the authors used the following data to build SEDs of the selected binary systems:
- mid infrared observations obtained with the VISIR instrument on UT3 of the ESO VLT, reported in the companion paper by Rahoui et al. (2008)
- mid infrared data taken from the Spitzer GLIMPSE survey
- X-ray observations taken with the space observatories INTEGRAL, XMM-Newton, RXTE, ASCA, BeppoSAX
From the SEDs the study allowed to identify the stellar counterpart of the X-ray sources and to reveal the nature of the companion star in each binary system. These multi-wavelength observations have shown that many of these sources are high-mass X-ray binaries hosting neutron stars orbiting around luminous and evolved supergiant companion stars.
INTEGRAL is therefore revealing a dominant class of obscured and short-lived high-energy binary systems that stellar population models should take into account for realistic estimates of high-energy binary systems in our Galaxy.