The X-ray source IGR J16318 - 4848 was the first source discovered by INTEGRAL on 2003 , January 29 .
The high energy spectrum exhibits such a high column density that the source is undetectable in X-rays below 2 keV .
On 2003 , February , 23–25 we triggered a Target of Opportunity ( ToO ) program using the EMMI and SOFI instruments on the New Technology Telescope of the European Southern Observatory ( La Silla ) to get optical and near-infrared ( NIR ) observations .
We discovered the optical counterpart , and confirmed the already proposed candidate in the NIR .
We report here photometric measurements in the R , I and J bands , upper flux limits in the Bb and V bands , lower flux limits in the H and K _ { s } bands .
We also got NIR spectroscopy between 0.95 and 2.52 \mbox { } \mu \mbox { m } , revealing a large amount of emission lines , including forbidden iron lines and P-Cygni profiles , and showing a strong similarity with CI Cam , another strongly absorbed source .
Together with the Spectral Energy Distribution ( SED ) , these data point to a high luminosity , high temperature source , with an intrinsic absorption greater than the interstellar absorption , but two orders of magnitude below the X-ray absorption .
We propose the following picture to match the data : the source is a High Mass X-ray binary ( HMXB ) at a distance between 0.9 and 6.2 kpc , the optical/NIR counterpart corresponds to the mass donor , which is 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 ] star as the mass donor after CI Cam .
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 .