Development and science perspectives of the POLAR-2 instrument: a large scale GRB polarimeter

Abstract

Despite several decades of multi-wavelength and multi-messenger spectral observations, Gamma-Ray Bursts (GRBs) remain one of the big mysteries of modern astrophysics. Polarization measurements are essential to gain a more clear and complete picture of the emission processes at work in these extremely powerful transient events. In this regard, a first generation of dedicated 𝛾-ray polarimeters, POLAR and GAP, were launched into space in the last decade. After 6 months of operation, the POLAR mission detected 55 GRBs, among which 14 have been analyzed in detail, reporting a low polarization degree and a hint of a temporal evolution of the polarization angle. Starting early 2024 and based on the legacy of the POLAR results, the POLAR-2 instrument will aim to provide a catalog of high quality measurements of the energy and temporal evolution of the GRB polarization thanks to its large and efficient polarimeter. Several spectrometer modules will additionally allow to perform joint spectral and polarization analyzes. The mission is foreseen to make high precision polarization measurements of about 50 GRBs every year on board of the China Space Station (CSS). The technical design of the polarimeter modules will be discussed in detail, as well as the expected scientific performances based on the first results of the developed prototype modules.

Gamma-Ray Polarimetry of the Crab Pulsar Observed by POLAR

“…POLAR-2 is a follow-up of the POLAR mission, which has been already selected to be launched to the China Space Station in around 2024 and will operate at least for two years (Kole 2019;Kole et al 2021;Hulsman 2020;De Angelis et al 2021). In order to improve the polarimetry precision, the POLAR-2 design takes two major improvements compared to POLAR, which are: 1) increasing the sensitive detector (scintillator array) modules from 25 to 100 (each module has 64 independent scintillator bars) so that the effective area will be approximately four times larger; 2) using a SiPM array (64 channels per module) together with its own front-end electronics (FEE) for readout which will lower the energy threshold of the detector pixel and increase the effective area at low energies.…”