POLAR-2: a large scale gamma-ray polarimeter for GRBs

TL;DR

POLAR-2 is a large-scale gamma-ray polarimeter designed to significantly improve polarization measurements of GRBs, aiming to enhance understanding of their physics through increased data collection and technological advancements.

Contribution

This paper introduces POLAR-2, a new gamma-ray polarimeter with increased sensitivity and technological upgrades, to provide more comprehensive polarization data for GRBs.

Findings

POLAR-2 will measure about 50 GRBs per year.

Design improvements include SiPMs and increased sensitive volume.

Expected to provide higher quality polarization data than POLAR.

Abstract

The prompt emission of GRBs has been investigated for more than 50 years but remains poorly understood. Commonly, spectral and temporal profiles of {\gamma}-ray emission are analysed. However, they are insufficient for a complete picture on GRB-related physics. The addition of polarization measurements provides invaluable information towards the understanding of these astrophysical sources. In recent years, dedicated polarimeters, such as POLAR and GAP, were built. The former of which observed low levels of polarization as well as a temporal evolution of the polarization angle. It was understood that a larger sample of GRB polarization measurements and time resolved studies are necessary to constrain theoretical models. The POLAR-2 mission aims to address this by increasing the effective area by an order of magnitude compared to POLAR. POLAR-2 is manifested for launch on board the China Space Station in 2024 and will operate for at least 2 years. Insight from POLAR will aid in the improvement of the overall POLAR-2 design. Major improvements (compared to POLAR) will include the replacement of multi-anode PMTs (MAPMTs) with SiPMs, increase in sensitive volume and further technological upgrades. POLAR-2 is projected to measure about 50 GRBs per year with equal or better quality compared to the best seen by POLAR. The instrument design, preliminary results and anticipated scientific potential of this mission will be discussed.