HRC-S Timing Mode Primer

This note describes the differences between choosing SCENTER and S_TIMING as observing modes for imaging with the HRC-S. There are two key differences. The first is related to the trigger threshold for event processing. For standard HRC observations, event processing is triggered when the event PHA is greater than or equal to 8. This is referred to as the lower level discriminator setting (LLD). In timing mode, this setting is raised to 21. This has the effect of rejecting most soft X-rays.

Second, when choosing SCENTER, edge blanking of the two outrigger plates is enabled. Event processing will discard any events which come from the outrigger plates. In S_TIMING mode, edge blanking is not enabled. Instead, outrigger plates are tied to ground and signals coming off the CGCD are not processed. This reduces the event rate to the science data processor, allowing for more accurate timing. In both S_CENTER and S_TIMING, vetoing is disabled. This is the default configuration for HRC-S (see HRCMODE defaults.

Users are cautioned against using S_TIMING unless high precision timing is required to achieve the science goals. Use of S_TIMING will result in a loss of low energy response, as all events with an event PHA less than 21 will be discarded via onboard processing.

Daniel Patnaude
Last modified: Wed Oct 20 11:29:46 EDT 2021