Properties of the background of EPIC onboard XMM-Newton

Abstract

Understanding a background is crucial in particular for a study of low surface brightness objects. In order to establish the background subtraction method, we have studied properties of the EPIC background. Count rates of the background vary violently by two order of magnitude at the maximum, while during the most quiet period, these are stable within 8 % at a 1 $σ$ level. The overall spectrum is dominated by particle events above 5 keV, and its spatial variation is also found. The long-term variation of the background is also investigated with CAL CLOSED data, which is the data of calibration source with filter closed. The average background count rate decreased by 20 % from March 2000 to January 2001, but it regained in February 2001. For the modeling of the background spectrum, we investigate correlations between the 2-10 keV count rate and some characteristic parameters. The PN background shows a good correlation with some parameters. On the other hands, the MOS background does not shows a clear correlation. Further investigation is needed for the MOS background. Our final goal is to establish a method to predict the background, for which these results will be reflected in the background generator.