In-orbit performance of HE onboard Insight -HXMT in the first 5 years

Purpose The high-energy X-ray telescope (HE), one of the three main payloads of the Insight -HXMT mission, is composed of eighteen NaI(Tl)/CsI(Na) phoswich detectors, where NaI(Tl) serves as the primary detector covering 20–250 keV, and CsI(Na) is used as an active shield detector to suppress the background of NaI(Tl) and also serves as an all-sky gamma-ray burst monitor covering 0.2–3 MeV. In this paper, we review the in-orbit performance of HE in the first 5 years since Insight -HXMT was launched on June 15, 2017. Methods The major performances we concern include the gain and energy resolution of NaI(Tl) and CsI(Na) detectors, the performance of pulse shape discriminator (PSD) and system dead time. In this work, we investigate these performances mainly using the data of blank-sky observations and the data when the telescope is in earth occultation. Results The overall performance of HE/NaI(Tl) is very stable in the first 5 years, whereas the gain of HE/CsI(Na) shows a continuously increasing trend and should be calibrated regularly. Conclusion In general, HE is still in good health and well-calibrated status after five-year’s operation. The in-orbit performance of HE has no significant deviation from expectation. HE is expected to be in operation healthily for another several years of extended mission life.