Five-year in-orbit background of Insight-HXMT

Purpose We present the five-year in-orbit background evolution of Insight -HXMT since the launch, as well as the effects of the background model in data analysis. Methods The backgrounds of the three main payloads, i.e., low-energy telescope, medium-energy telescope, and high-energy telescope, are described. The evolution of the background over time is obtained by simply comparing the background in every year during the in-orbit operation of Insight -HXMT. Results The major observational characteristics of the Insight -HXMT in-orbit background are presented, including the light curve, spectrum, geographical distribution, and long-term evolution. The systematic error in background estimation is investigated for every year. Conclusion The observational characteristics of the five-year in-orbit background are consistent with our knowledge of the satellite design and the space environment, and the background model is still valid for the latest observations of Insight -HXMT.