Revealing the Nature of the Obscured High Mass X-ray Binary IGR J16318-4848 |
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| Authors: | Sylvain Chaty Philippe Filliatre |
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| Institution: | (1) Université Paris 7 Denis-Diderot, 2 Place Jussieu, Paris Cedex 05, France;(2) Service d’Astrophysique, CEA-Saclay, France |
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| Abstract: | The X-ray source IGR J16318-4848 was the first source discovered by INTEGRAL on January 29, 2003. The high energy spectrum
exhibits such a high column density that the source is undetectable in X-rays below 2 keV. On February 23–25, 2003 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. NIR spectroscopy revealed a large amount of emission lines, including
forbidden iron lines and P-Cygni profiles, 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. All these observations
show that IGR J16318-4848 is a high mass X-ray binary (HMXB) at a distance between 0.9 and 6.2 kpc, the mass donor being an
early-type star, probably a sgBe] star, surrounded by a dense and absorbing circumstellar material. This would make the second
HMXB with a sgBe] star as the mass donor after CI Cam.
Other sources, discovered by INTEGRAL near IGR J16318-4848 in the direction of the Norma arm, present the same characteristics,
at least in X-rays. 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.
Out of the 15 sources present in this region, only one might be associated with an unidentified EGRET source: IGR J16393-4643.
Therefore these obscured INTEGRAL sources do not seem to be powerful high energy (E > 100 MeV) emitters.
Based on observations collected at the European Southern Observatory, Chile (proposal ESO N∘ 70.D-0340). |
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| Keywords: | stars: circumstellar matter emission-line Be– X-rays: binaries IGR J16318-4848 |
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