In-orbit background simulation of a type-B CATCH satellite

TL;DR

This paper simulates the in-orbit background for a type-B CATCH satellite to optimize its design and sensitivity, identifying dominant background sources and assessing shielding needs.

Contribution

It provides a detailed in-orbit background simulation for a type-B CATCH satellite using Geant4, highlighting background sources and implications for shielding.

Findings

Persistent background dominated by cosmic X-ray and cosmic-ray protons.

Dynamic background mainly from trapped electrons outside the aperture.

Estimated observation sensitivity of 4.22×10⁻¹³ erg cm⁻² s⁻¹.

Abstract

The Chasing All Transients Constellation Hunters (CATCH) space mission plans to launch three types of micro-satellites (A, B, and C). The type-B CATCH satellites are dedicated to locating transients and detecting their time-dependent energy spectra. A type-B satellite is equipped with lightweight Wolter-I X-ray optics and an array of position-sensitive multi-pixel Silicon Drift Detectors. To optimize the scientific payloads for operating properly in orbit and performing the observations with high sensitivities, this work performs an in-orbit background simulation of a type-B CATCH satellite using the Geant4 toolkit. It shows that the persistent background is dominated by the cosmic X-ray diffuse background and the cosmic-ray protons. The dynamic background is also estimated considering trapped charged particles in the radiation belts and low-energy charged particles near the geomagnetic equator, which is dominated by the incident electrons outside the aperture. The simulated persistent background within the focal spot is used to estimate the observation sensitivity, i.e. 4.22$\times$10$^{-13}$ erg cm$^{-2}$ s$^{-1}$ with an exposure of 10$^{4}$ s and a Crab-like source spectrum, which can be utilized further to optimize the shielding design. The simulated in-orbit background also suggests that the magnetic diverter just underneath the optics may be unnecessary in this kind of micro-satellites, because the dynamic background induced by charged particles outside the aperture is around 3 orders of magnitude larger than that inside the aperture.