prf -- Description of the point response functions, PRF, for ROSAT and Einstein
This document describes the PRF (a.k.a. PSF) for the appropriate instruments and gives tables of in-orbit calibration images available to PROS.
The point response function, PRF, (aka point spread function, PSF) of each detector/mirror combination describes the spatial distribution of counts from an unresolved source. On-axis, it is usually found to be circularly symmetric except for radial spokes caused by the mirror support ribs. Off axis, the PRF gets distorted by coma and other aberrations. To first order, the PRF is a function of energy and off-axis distance. To second order, there will be variations from relative position of detector wires and there also may be distortions from imperfect corrections for gaps (HRI) or other algorithms used to compensate for known hardware non-linear behavior. In these referenced memos, we will partially address only the first order effects. We have included PRF information with the PROS release because there are many applications and uses (e.g. an immodel future enhancement will allow the convolution of a selected PRF with a chosen model). In the 4 mission+focal-plane-detector descriptions we provide analytic approximations, usually restricted to on-axis characteristic based on some set of observations with a limited number of energy distributions. We also describe the set of images supplied: both actual observations of sources known or thought to be essentially unresolved and data from ground calibrations (monochromatic). These two sorts are loosely described by the terms "Sky CALs" and "Ground CALs". There are four help files with the following names: prfroshri The Rosat HRI+mirror data in directory xrcal$ prfrospspc The Rosat PSPC + mirror data in directory xrcal$ prfeoipc The Einstein IPC + mirror data in directory xecal$ prfeohri The Einstein HRI + mirror data in directory xecal$