INTEGRAL's sharper view of the hard X-ray sky
The circular structures in the OSA 8 enhanced background image are artefacts related to the absorption of hard X-ray photons by the glue used to mount the instrument coded mask on its supporting structure. The intensity of these artefacts for OSA 8 is of the order of 0.2% of that of the brightest source in the field of view.
Thanks to an extensive in-flight calibration effort this glue could be modelled much better, reducing the artefacts by a factor of 10 for OSA 9 (right panel). In this image, new faint hard X-ray sources could now be detected for the first time. The source in the green circle, for example, is two thousand times fainter than Cygnus X-1.
The OSA 9 software package is available at the INTEGRAL Science Data Centre (http://www.isdc.unige.ch/integral/).