The SAS-2 psf file is in the standard psf FITS format for X-ray astronomy (see the document CAL/GEN/92-018). Columns 1, 2, and 5 have the same definition as in that document. The exception is columns 3 and 4. Though the column names (RAD_LO and RAD_HI) are the same, their meanings differ significantly from that of X-ray imaging detectors where the X-ray is given as a position on a 2-dimensional grid. For the detection of high energy -rays where a sparkchamber is used, such a grid does not exist and therefore the concept of radial distance is undefined. Instead the zenith and azimuth angles of the event with respect to the telescope's z-axis is recorded and therefore the probability of detecting an event depends upon zenith angle.
The psf of sparkchamber depends on zenith angle and strongly on energy, since high energy -rays have their direction more accurately know. The direction of the -ray cannot generally be determined to better than 0.1 degree. The psf is given for seven energy ranges and two zenith angles.
Brenden Perry (HEASARC)
No information supllied to the CALDB other than that above.