The Background Model of the Medium Energy X-ray telescope of Insight-HXMT

Abstract

The Medium Energy X-ray Telescope (ME) is one of the main payloads of the Hard X-ray Modulation Telescope (dubbed as Insight-HXMT ). The background of Insight-HXMT /ME is mainly caused by the environmental charged particles and the background intensity is modulated remarkably by the geomagnetic field, as well as the geographical location. At the same geographical location, the background spectral shape is stable but the intensity varies with the level of the environmental charged particles. In this paper, we develop a model to estimate the ME background based on the ME database that is established with the two-year blank sky observations of the high Galactic latitude. In this model, the entire geographical area covered by Insight-HXMT is divided into grids of 5 • × 5 • in geographical coordinate system. For each grid, the background spectral shape can be obtained from the background database and the intensity can be corrected by the contemporary count rate of the blind FOV detectors. Thus the background spectrum can be obtained by accumulating the background of all the grids passed by Insight-HXMT during the effective observational time. The model test with the blank sky observations shows that the systematic error of the background estimation in 8.9 − 44.0 keV is ∼ 1.3% for a pointing observation with an average exposure ∼ 5.5 ks. We also find that the systematic error is anti-correlated with the exposure, which indicates the systematic error is partly contributed by the statistical error of count rate measured by the blind FOV detectors.

Spectral evolution of X-ray pulsar 4U 1901+03 during the 2019 outburst based on Insight-HXMT and NuSTAR observations

“…Therefore, we decided to use only LE and ME data covering the energy range between 1 and 30 keV in this work. In order to reduce the HXMT data and extract the source spectra, we performed the standard data reduction procedure ex- plained in the Insight-HXMT official user guide 1 using the software HXMTSOFT v 2.01 (Li et al 2020;Liao et al 2020b,a;Guo et al 2020).…”

Comparison of simulated backgrounds with in-orbit observations for HE, ME, and LE onboard Insight-HXMT

“…Take the LE background as an example, there are several hundred seconds flares below 7 keV presented in the light curve, which may result from the real-time low-energy charged particles (Liao et al 2020). The observed ME background rates could vary by up to 50% even in the same COR region (Guo et al 2020). In addition, the relative direction of the Earth in the FOV has some effects on the background.…”

Phase dependent evolution within large luminosity range of 1A 0535+262 observed by Insight-HXMT during 2020 giant outburst

“…Because of the uncertain calibration of Ag emission line at ∼ 22 keV of the ME, we ignore the 20 − 23 keV range during the spectral analysis for this instrument. The instrumental backgrounds are estimated with the tools provided by Insight-HXMT team: LEBKGMAP, MEBKGMAP and HEBKGMAP, version 2.0.9 based on the standard Insight-HXMT background models (Liao et al 2020a;Liao et al 2020b;Guo et al 2020). The XSPEC v12.12.0 software package (Arnaud 1996) was used to perform the spectral fitting.…”