# Geant4 Simulations Of A Wide-Angle X-Ray Focusing Telescope

## TL;DR

This paper develops a Geant4-based Monte Carlo model for simulating wide-angle X-ray focusing telescopes with lobster-eye optics, addressing physical process gaps and validating the model against existing software.

## Contribution

It introduces a novel Geant4 simulation framework for X-ray telescopes, incorporating grazing incidence reflection and proton scattering processes.

## Key findings

- Effective area matches Q software within 3%
- X-ray background dominates below 10 keV
- Telescope sensitivity exceeds coded mask designs by over tenfold

## Abstract

The rapid development of X-ray astronomy has been made possible by widely deploying X-ray focusing telescopes on board many X-ray satellites. Geant4 is a very powerful toolkit for Monte Carlo simulations and has remarkable abilities to model complex geometrical configurations. However, the library of physical processes available in Geant4 lacks a description of the reflection of X-ray photons at a grazing incident angle which is the core physical process in the simulation of X-ray focusing telescopes. The scattering of low-energy charged particles from the mirror surfaces is another noteworthy process which is not yet incorporated into Geant4. Here we describe a Monte Carlo model of a simplified wide-angle X-ray focusing telescope adopting lobster-eye optics and a silicon detector using the Geant4 toolkit. With this model, we simulate the X-ray tracing, proton scattering and background detection. We find that: (1) the effective area obtained using Geant4 is in agreement with that obtained using Q software with an average difference of less than 3\%; (2) X-rays are the dominant background source below 10 keV; (3) the sensitivity of the telescope is better by at least one order of magnitude than that of a coded mask telescope with the same physical dimensions; (4) the number of protons passing through the optics and reaching the detector by Firsov scattering is about 2.5 times that of multiple scattering for the lobster-eye telescope.