Multi-wavelength observations revealing the most obscured high energy sources of our Galaxy

A new type of high-energy binary system has been revealed by the INTEGRAL satellite. These sources are being unveiled by means of multi-wavelength optical, near- and mid-infrared observations. Among these sources, two distinct classes are appearing: the first one is constituted of intrinsically obscured high-energy sources, of which IGR J16318-4848 seems to be the most extreme example. The second one is populated by the so-called supergiant fast X-ray transients, with IGR J17544-2619 being the archetype. We first give here a general introduction on INTEGRAL sources, before reporting on multi-wavelength optical to mid-infrared observations of a sample constituted of 21 INTEGRAL sources. We show that in the case of the obscured sources our observations suggest the presence of absorbing material (dust and/or cold gas) enshrouding the whole binary system. We finally discuss the nature of these two different types of sources, in the context of high energy binary systems, and give a scenario of unification of all these different types of high energy sources, based on their high energy properties.