INTEGRAL reveals a new class of obscured high mass X-ray binaries: Focus on IGR J16318-4848

The X-ray source IGR J16318-4848 is the first source discovered by INTEGRAL on 2003, January 29, exhibiting a very high column density. On 2003, February, 23-25 we triggered a Target of Opportunity (ToO) program using the EMMI (optical) and SOFI (near-infrared, NIR) instruments on the New Technology Telescope of the European Southern Observatory (NTT/ESO La Silla). We discovered the optical counterpart and confirmed the NIR candidate. NIR spectroscopy revealed a large amount of emission lines, including forbidden iron and P-Cygni profiles. We show that the source is a High Mass X-ray binary (HMXB) at a distance between 0.9 and 6.2kpc, the mass donor being an early-type star, probably a sgB[e] star, surrounded by a dense and absorbing circumstellar material. This would make the second HMXB with a sgB[e] after CI Cam. Other sources, discovered by INTEGRAL near ICR J16318-4848 in the direction of the Norma arm, present the same characteristics. Such sources may represent a different evolutionary state of X-ray binaries previously undetected with the lower energy space telescopes; if it is so, a new class of strongly absorbed X-ray binaries is being unveiled by INTEGRAL.