We recommend that TIME-TAG mode always be used with FLASH=YES (the so-called TAGFLASH mode) unless circumstances prevent it (see Section 5.7.1). ACCUM mode should be used for such high count-rate targets. At present, TIME-TAG should not be used for count rates greater than 30,000 count/s. At count rates between 21,000 and 30,000 count/s, TIME-TAG may be used to obtain properly flux-calibrated data, but the loss of some continuous time periods within extended exposures will occur (see the discussion of the buffer time in Section 5.4). TIME-TAG mode should always be used for exposures that will generate count rates of 21,000 count/s or less from the entire detector (including both detector segments for the FUV). When data are processed by the ground system arrival times are assigned to the events according to the time marker preceding the event.ĬOS observations should be obtained in TIME-TAG mode whenever possible because it provides significant opportunities for temporal sampling, exclusion of poor quality data, and, for the FUV, improved thermal correction (by tracking the stim-pulse positions as a function of time) and background removal (by using the pulse-height information). Time markers are inserted in the list every 32 ms by the instrument electronics. Each entry in that list contains the ( x, y) coordinates of the photon together with the pulse height of the charge cloud generated by it (for FUV observations). In TIME-TAG mode each photon is kept as a separate event in a list in COS memory. COS exposures may be obtained in either a time-tagged photon-address mode ( TIME-TAG), in which the position, arrival time, and pulse height (for FUV observations) of each detected photon are saved in an event stream, or in accumulation ( ACCUM) mode, in which only the positions of the photon events are recorded.
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