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The dead time of the PSPC due to X-ray events was determined between tex2html_wrap_inline1970 s and tex2html_wrap_inline1972 s per event depending on pulse height; the dead time due to particle events is about tex2html_wrap_inline1974 s. For ``typical'' ROSAT observations, i.e., observations with the total (accepted) X-ray event rate being less than tex2html_wrap_inline1976  counts s tex2html_wrap_inline1894 , deadtime will be almost exclusively caused by the count rate due to particle background events; for particle background rates of 100 counts s tex2html_wrap_inline1894 , the dead time is tex2html_wrap_inline1982 percent and for the maximal background rate of 400 counts s tex2html_wrap_inline1894 , this increases to tex2html_wrap_inline1986 percent.

While each recorded PSPC event is time-tagged, the electronics allows only an effective resolution of tex2html_wrap_inline1988 s; this accuracy applies only to the relative arrival times of recorded events. The accuracy of absolute timing with respect to UT is on the order of a few milliseconds.

Michael Arida
Tue Jun 11 16:18:41 EDT 1996