Performance study of swept charge device array in orbit

Abstract

The Low Energy X-ray Telescope (LE) is one of the three scientific instruments onboard the Insight-Hard X-ray Modulation Telescope (Insight-HXMT). Its primary scientific objectives include conducting both scanning and pointed observations within the soft X-ray band, specifically from 0.7 keV to 13 keV. The LE utilizes a Swept Charge Device (SCD) and forms a large-area array, achieving good energy resolution and time resolution. Due to exposure to space radiation, the performance of the detector gradually declines. By analyzing almost 7 years of LE onboard data, we studied the changes in detector performance and their underlying causes, including aspects such as readout noise, energy resolution, detector gain, and the proportion of split events. The results indicate that the readout noise increases continuously over time; the noise peak position drifts gradually; the energy resolution degrades at a rate of 50–60 eV per year, primarily due to the increasing charge transfer inefficiency; the detector gain decreases by approximately 0.8–1.3% each year; and the variation in the proportion of split events is only related to the detector threshold and is independent of space radiation. These studies provide important references for determining the LE observation plan and for analyzing the performance evolution of similar semiconductor detectors.