Prospects of measuring Gamma-ray Burst Polarisation with the Daksha mission

TL;DR

The paper evaluates Daksha's potential to measure gamma-ray burst polarization using simulations, showing it can detect polarization levels of around 30% for bright GRBs, enabling polarization studies of about five GRBs annually.

Contribution

This study demonstrates Daksha's gamma-ray polarization measurement capabilities and estimates its sensitivity, a novel assessment for this upcoming space mission.

Findings

Daksha can measure polarization with a minimum detectable polarization of ~30%.

It can potentially measure polarization in about five GRBs per year.

Simulations confirm the effectiveness of CZT detectors for polarization studies.

Abstract

The proposed Daksha mission comprises of a pair of highly sensitive space telescopes for detecting and characterising high-energy transients such as electromagnetic counterparts of gravitational wave events and gamma-ray bursts (GRBs). Along with spectral and timing analysis, Daksha can also undertake polarisation studies of these transients, providing data crucial for understanding the source geometry and physical processes governing high-energy emission. Each Daksha satellite will have 340 pixelated Cadmium Zinc Telluride (CZT) detectors arranged in a quasi-hemispherical configuration without any field-of-view collimation (open detectors). These CZT detectors are good polarimeters in the energy range 100 -- 400 keV, and their ability to measure polarisation has been successfully demonstrated by the Cadmium Zinc Telluride Imager (CZTI) onboard AstroSat. Here we demonstrate the hard X-ray polarisation measurement capabilities of Daksha and estimate the polarisation measurement sensitivity (in terms of the Minimum Detectable Polarisation: MDP) using extensive simulations. We find that Daksha will have MDP of~$30\%$ for a fluence threshold of $10^{-4}$ erg cm$^2$ (in 10 -- 1000 keV). We estimate that with this sensitivity, if GRBs are highly polarised, Daksha can measure the polarisation of about five GRBs per year.