THE CALIBRATION OF THE ROSAT HRI PARTICLE BACKGROUND

A calibration for the particle background (PB) of the ROSAT High Resol ution Imager (HRI) is presented. It is found that the PB rate is tempo rally a relatively stable function of the subsatellite geographic posi tion and that the average master veto (MV) signal of the Position Sens itive Proportional Counter is a good template of that function. By det ermining the general correlation between the average MV signal and PB rate as a function of time and scaling the general correlation by an i ndividual observation's light curve, an accurate PB model for that obs ervation can be produced. Detector maps for the distribution of PB eve nts and the distribution of exposure (including vignetting, detector a rtifacts, and quantum efficiency variations) are also presented. The m aps were created from Earth-block data collected throughout the missio n.