Optimizing the Search for High-z GRBs: The JANUS X-ray Coded Aperture Telescope

TL;DR

This paper optimizes the design of the JANUS X-ray telescope to maximize high-redshift gamma-ray burst detections, concluding that a coded aperture design in the below 30 keV energy band is most effective, predicting four times more detections than alternative designs.

Contribution

It identifies the optimal energy band and detector design for high-z GRB detection, demonstrating the superiority of coded aperture over lobster-eye designs within mission constraints.

Findings

Coded aperture design detects four times more high-z GRBs than lobster-eye.

Optimal detection energy band is below 30 keV.

JANUS XCAT will detect 48 GRBs with z > 5 in two years.

Abstract

We discuss the optimization of gamma-ray burst (GRB) detectors with a goal of maximizing the detected number of bright high-redshift GRBs, in the context of design studies conducted for the X-ray transient detector on the JANUS mission. We conclude that the optimal energy band for detection of high-z GRBs is below about 30 keV. We considered both lobster-eye and coded aperture designs operating in this energy band. Within the available mass and power constraints, we found that the coded aperture mask was preferred for the detection of high-z bursts with bright enough afterglows to probe galaxies in the era of the Cosmic Dawn. This initial conclusion was confirmed through detailed mission simulations that found that the selected design (an X-ray Coded Aperture Telescope) would detect four times as many bright, high-z GRBs as the lobster-eye design we considered. The JANUS XCAT instrument will detect 48 GRBs with z > 5 and fluence Sx > 3 {\times} 10-7 erg cm-2 in a two year mission.