THE PARTICLE BACKGROUND OF THE ROSAT PSPC

In order to permit quantitative studies of the diffuse cosmic X-ray background and of extended X-ray sources, we have parameterized the particle induced background of the Roentgen Satellite, ROSAT, Position Sensitive Proportional Counter (PSPC). Data collected during 2.1 x 10(5) s of PSPC operation have been analyzed and the temporal, spectral, and spatial distributions, investigated. The PSPC rejection of these unwanted events is exceptionally efficient with a typical residua count rate of roughly 1 x 10(-3) counts s-1 cm-2 keV-1 or 5 x 10(6) counts s-1 arcmin-2 keV-1. About 77% of the residual events originate within the detector while the remainder enter through the counter window. During typical conditions, the count rate of the residual events is well correlated with the Master Veto (MV) count rate. The spectrum of these events is well described by a flat component plus a soft power law and an A1 K-alpha line at 1.5 keV. Also during typical conditions, the ratio between the power law and flat components remains constant to +/-4% while the relative Al K-alpha contribution increases with increasing MV count rate. The distribution of the counts over the field of view is uniform except for a slight radial dependence and shadowing caused by blockage of the externally produced component by the window support structure.