Improved positions for unidentified INTEGRAL sources in the 4th INTEGRAL/IBIS sky survey catalogue
(Originally published as an INTEGRAL Picture of the Month on the INTEGRAL science operations centre website.)
The 4th INTEGRAL/IBIS sky survey catalogue (Bird et al. ApJS 186, 1, 2010, see also the related image) contains more than 700 sources in the 17-100 keV energy range. About 29% of the catalogued sources are as yet unidentified and/or unclassified.
As part of the ongoing campaign to identify the remaining unknown sources, the use of X-ray catalogues is extremely important. By performing a statistical correlation analysis between the gamma-ray source positions and the X-ray lists, it is possible to find objects which have X-ray counterparts at high statistical probabilities. The X-ray sources have in general a much more precise position and this can then be used for follow-up observations at other wavelengths, which may then lead to the source classification.
The picture shows one example: the unidentified 4th INTEGRAL/IBIS sky survey catalogue object IGR J17488-2338 (green IBIS location error circle) can be associated with the XMM Slew Survey source XMMSL1 J174838.8 -233537 (the much smaller white XMM location error circle). This X-ray source is centred on the nucleus of a bright radio source with a double lobe morphology (the background image is from the NRAO VLA Sky Survey (NVSS), at 1.4 GHz). Thus the counterpart of the INTEGRAL source IGR J17488-2338 can be identified as a new active galaxy behind the Galactic plane (it's position on the sky is within 10° from our Galactic plane).