XMM-Newton Science Analysis System: User Guide

6.7.7 The Jupiter patch

In XMM-Newton revolution 3224, two accidental exposures of Jupiter, with the V filter, were executed. Due to the extreme source intensity, this caused some persistent damage to the photocathode, resulting in a small patch of degraded sensitivity near the centre of the OM field of view. This is decsribed in the OM Calibration Status document. The patch is an elliptical region with major and minor axes of 105 arcsecs x 60 arcsecs, whose throughput is position and wavelength dependent but is depressed by as much as 35% i n the V filter. Sources in the main part of the patch are flagged during SAS processing. However, sources in the outer wings of the patch are not currently flagged and this annular zone includes the location of the EPIC pn boresight, where many targets are located. At the EPIC pn boresight, the throughput is suppressed by around 8% in the V filter and a few percent in the UV filters. Importantly, at the current time, the effects of the sensitivity loss over the patch as a whole, are not corrected for in SAS processing. However, a specific, local correction is now applied (first introduced in SAS v22) to sources detected within 7.5 arcsecs of the EPIC pn boresight position, this being the location where targets are generally positioned. Users should be aware that, if observed after revolution 3224, the Jupiter patch could affect other sources of interest and they may need to allow for the impact of the degradation. Users should also note that grism spectra (especially targets observed in the default grism window) may be affected by the patch over limited wavelength ranges in both the UV and Visible grisms, by up to about 25%. Again, the impact of the patch on the grism data is not corrected for by the SAS, currently.