The COS-B 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 meaning as in that document. The exception is columns 3
and 4. Though the column names (RAD_LO and RAD_HI) are the same,
their meaning differs significantly from that of X-ray imaging
detectors where the X-ray event is given as a position on a
2-dimensional grid. For the detection of high energy 
-rays
where a spark-chamber is used, such a grid does not exist and
therefore the concept of radial distance does not exist. 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 spark-chambers depends strongly on energy. Since high energy electrons and positrons are less affected by multiple Coulomb scattering, their direction is more accurately know. Thus the psf is given for three energy ranges and a maximum zenith angle of 20 degrees in 0.2 degree increments.
Brenden Perry (HEASARC)
HDUDOC/VERS = CAL/GEN/92-018/1.0.0
(see CAL/GEN/92-018).
No information supllied to the CALDB other than that above.
