Imaging and burst location with the EXIST high-energy telescope

TL;DR

The paper discusses the design, simulation, and analysis of a high-energy coded mask telescope for the EXIST mission, focusing on imaging, burst localization, and minimizing systematic errors in a scanning sky survey.

Contribution

It introduces a novel two-scale coded mask design and a two-step burst localization method, validated through Monte Carlo simulations and analytic analysis.

Findings

Design achieves near photon-limited imaging performance.

Two-step localization effectively detects and localizes gamma-ray bursts.

Scanning mode reduces systematic errors and provides all-sky coverage.

Abstract

The primary instrument of the proposed EXIST mission is a coded mask high energy telescope (the HET), that must have a wide field of view and extremely good sensitivity. It will be crucial to minimize systematic errors so that even for very long total integration times the imaging performance is close to the statistical photon limit. There is also a requirement to be able to reconstruct images on-board in near real time in order to detect and localize gamma-ray bursts. This must be done while the spacecraft is scanning the sky. The scanning provides all-sky coverage and is key to reducing systematic errors. The on-board computational problem is made even more challenging for EXIST by the very large number of detector pixels. Numerous alternative designs for the HET have been evaluated. The baseline concept adopted depends on a unique coded mask with two spatial scales. Monte Carlo simulations and analytic analysis techniques have been used to demonstrate the capabilities of the design and of the proposed two-step burst localization procedure.