Geant4 simulations of a wide-angle x-ray focusing telescope
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.
KeywordsX-ray telescope Geant4 Lobster-eye optics Scattering of charged particles Background Sensitivity
This work is supported by the Strategic Priority Research Program on Space Science, the Chinese Academy of Sciences, Grant No. XDA04061100, the programs of National Natural Science Foundation of China under the Grant No.11403055, No.11203043 and No.11427804, China Post-doctoral Science Foundation under the Grant No.2014M561068, and the Young Researcher Grant of National Astronomical Observatories, Chinese Academy of Sciences.
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