A Description of the PSF

The ROSAT PSF describes the spatial response of the instrument to a point source resulting from the scattering of photons due to mirror figuring and irregularities, and physical limitations of the detector. This response also varies with energy.

The PSF has to be considered to perform an optimal analysis of an observation.

The PSF results from a number of factors;

ON AXIS effects - see OGIP calibration memo. CAL/ROS/92-001.

• A scattering effect - caused by irregularities in the surface of the mirror.
• A penetration effect - due to the varying depth penetration of X-rays in the counter gas.
• A resolution effect - because of the manner in which electrons are generated.
• Image ghosting - in PHA channels less than channel 15.
• An ellipsoidal blur - due to the uncorrected attitude motion.

OFF AXIS effect - see OGIP calibration memo. CAL/ROS/93-015.

• A blur effect - the blur of the XMA.