IGR J16318-4848: An X-ray Source in a Dense Envelope?

Abstract

We analyze in detail the ASCA observations of the hard X-ray source IGR J16318-4848, which was recently discovered by the INTEGRAL observatory (Courvoisier et al. 2003). The source has an anomalously hard spectrum in the energy range 0.5-10 keV and is virtually undetectable below 4 keV because of strong photoabsorption (n_H L > 4 x 10²³ cm^{-2}). The K line of neutral or weakly ionized iron with an equivalent width of 2.5 keV dominates in the energy range 4-10 keV. There is also evidence for the presence of a second line at energy 7 keV. Our analysis of archival observational data for the infrared counterpart of IGR J16318-4848 that was discovered by Foschini et al. (2003) revealed the source in the wavelength range 1-15 micrometers. Available data suggest that the object can be an X-ray binary system surrounded by a dense envelope. The source may be a high-mass X-ray binary similar to GX 301-2. We believe that IGR J16318-4848 can be the first representative of a hitherto unknown population of strongly absorbed Galactic X-ray sources that could not be detected by previous X-ray observatories.