Simulation of the In-flight Background for HXMT/HE

TL;DR

This paper models the in-flight background for HXMT/HE using detailed simulations of space environment interactions, providing insights into background levels, dominant components, and instrument sensitivity for X-ray astronomy.

Contribution

It introduces a comprehensive geometric and environmental simulation approach to estimate HXMT/HE background, including cosmic rays and atmospheric interactions.

Findings

Total background is about 540 counts/sec in 20-250 keV

Cosmic rays and SAA trapped particles dominate the background

Sensitivity estimated at approximately 0.1 mCrab at 50 keV

Abstract

The Hard X-ray Modulation Telescope (HXMT) is a broad band X-ray astronomical satellite from 1 to 250 keV. Understanding the X-ray background in detail will help to achieve a good performance of the instrument. In this work, we make use of the mass modelling technique to estimate the background of High Energy Telescope (HE) aboard HXMT. It consists of three steps. First, we built a complete geometric model of HXMT. Then based on the investigation about the space environment concerning HXMT low-earth orbit, in our simulation we considered cosmic rays, cosmic X-ray background (CXB), South Atlantic Anomaly (SAA) trapped particles, the albedo gamma and neutrons from interaction of cosmic rays with the Earth's atmosphere. Finally, the Shielding Physics List supplied by Geant4 collaborations was adopted. According to our simulation, (1) the total background of HXMT/HE is about 540 count/s on average over 20-250 keV energy band after 100 days in orbit; (2) the delayed component caused by cosmic rays and SAA trapped particles dominates the full energy band of HXMT/HE; (3) some emission lines are prominent in the background continuum spectrum and will be used for in-orbit calibration; (4) the estimated sensitivity is approximately 0.1 mCrab at 50 keV with an exposure of $10^{6}$ s.