# A Combined Compton and Coded-aperture Telescope for Medium-energy Gamma-ray Astrophysics

## TL;DR

This paper presents the design and simulation of a combined Compton and coded-aperture gamma-ray telescope using CdZnTe detectors and a silicon tracker, aiming for high sensitivity and resolution in medium-energy gamma-ray astrophysics.

## Contribution

It introduces a novel combined Compton and coded-aperture telescope design with detailed simulation results demonstrating high energy and angular resolution capabilities.

## Key findings

- Achieves 1.68% FWHM energy resolution at 511 keV
- On-axis angular resolution of 2.63° at 511 keV
- Effective area of 183 cm² at 511 keV

## Abstract

A future mission in medium-energy gamma-ray astrophysics would allow for many scientific advancements, e.g. a possible explanation for the excess positron emission from the Galactic Center, a better understanding of nucleosynthesis and explosion mechanisms in Type Ia supernovae, and a look at the physical forces at play in compact objects such as black holes and neutron stars. Additionally, further observation in this energy regime would significantly extend the search parameter space for low-mass dark matter. In order to achieve these objectives, an instrument with good energy resolution, good angular resolution, and high sensitivity is required. In this paper we present the design and simulation of a Compton telescope consisting of cubic-centimeter Cadmium Zinc Telluride (CdZnTe) detectors as absorbers behind a silicon tracker with the addition of a passive coded mask. The goal of the design was to create a very sensitive instrument that is capable of high angular resolution. The simulated telescope showed achievable energy resolutions of 1.68$\%$ FWHM at 511 keV and 1.11$\%$ at 1809 keV, on-axis angular resolutions in Compton mode of 2.63$^{\circ}$ FWHM at 511 keV and 1.30$^{\circ}$ FWHM at 1809 keV, and is capable of resolving sources to at least 0.2$^{\circ}$ at lower energies with the use of the coded mask. An initial assessment of the instrument in Compton imaging mode yields an effective area of 183 cm$^{2}$ at 511 keV and an anticipated all-sky sensitivity of 3.6 x 10$^{-6}$ photons cm$^{-2}$ s$^{-1}$ for a broadened 511 keV source over a 2-year observation time. Additionally, combining a coded mask with a Compton imager to improve point source localization for positron detection has been demonstrated.