|ROSAT Home Page||ROSAT The time variability of X-ray emission
can be studied with the HRI since each detected photon has its
time of arrival recorded by the detector. The accuracy of this
time is limited by the electronic resolution of the HRI
processor which is 61 sec relative to the ROSAT spacecraft
clock. The relative arrival times of photons during a single
observation is accurate to this value. The absolute accuracy of
the ROSAT spacecraft clock, and its conversion to UT, is
expected to be a few milliseconds. The HRI has a processing dead
time during which events may not be counted which varies between
0.36 and 1.35 msec per event. The variation is discussed in
section 188.8.131.52 and depends on the fine position of the
event. Thus there is a dead time correction that needs to be
made for calculating the true event rate from a source. A mean
dead time of = 0.81 msec can be used for this purpose, and the
true rate is then given by: , where n is the observed rate. Due
to the telescope wobble and the smal