Deadtime calculation method of the High Energy x-ray telescope (HE) onboard the Insight-HXMT satellite

Deadtime is the time period during which a detector processes the previous photon event and any later events will be ignored, thus the calculation of deadtime is of great importance to reconstruct the incident photon flux from the recorded counts. The High Energy X-ray telescope (HE) on-board the Insight-HXMT satellite records the deadtime only for a fixed time bin (i.e. 1 s), therefore it is impossible to directly obtain the deadtime for an arbitrary time interval, especially for high-energy transients much shorter than one second. Based on the electronics model of HE, we establish a deadtime calculation method to derive the deadtime in any time interval. We apply this method to transient sources observed by HE, including Gamma-ray Bursts (GRB) and Terrestrial Gamma-ray Flashes (TGF). Furthermore, since the data processing capacity of HE electronics is limited, HE suffers data saturation for very bright GRBs. During the saturation period, a significant part of counts signal cannot be recorded. We find that the amount of lost counts can be estimated by comparing the recorded 1 s deadtime and the calculated deadtime using the method mentioned above.