treatdeadtime

XMM-Newton Science Analysis System

lccorr (lccorr-2.22.2) [xmmsas_20050815_1803-6.5.0]

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treatdeadtime

Part of the ccd frame duration (T $_{\rm f}$ ) is taken up by two sorts of dead time. The first is the time taken to read the ccd row by row (T $_{\rm r}$ ). Events occurring during T $_{\rm r}$ are called out-of-time events (OOTEs) and are spread over the whole ccd column (see reference [2], for more details). If the source collection region has a small extent in the column direction, most of the OOTEs from sources nominally within the collection region will not fall within it and will therefore not find their way into the TS. An approximate correction can be calculated by evaluating $T_{\rm f} / (T_{\rm f} - T_{\rm r})$ (the smaller the extent of the region in the column direction, the better the approximation will be).

In some instrument modes there is an additional period of `true' dead time, during which events are not recorded at all. For these modes the additional dead time is added to T $_{\rm r}$ in the expression above and the calculation carried out as before.

The quantity T $_{\rm f}$ - T $_{\rm r}$ is obtainable from the TIMEDEL column or keyword of the EXPOSUnn extensions of the event list, whereas the readout and other times are contained in the CCF.

XMM-Newton SOC/SSC -- 2005-08-16