POLAR-2, the next generation of GRB polarization detector

Abstract

The POLAR-2 Gamma-Ray Burst (GRB) Polarimetry mission is a follow-up to the successful POLAR mission. POLAR collected six months of data in 2016-2017 on board the Tiangong-2 Chinese Space laboratory. From a polarization study on 14 GRBs, POLAR measured an overall low polarization and a hint for an unexpected complexity in the time evolution of polarization during GRBs. Energy-dependent measurements of the GRB polarization will be presented by N. de Angelis in GA21-09 (August 2nd). These results demonstrate the need for measurements with significantly improved accuracy. Moreover, the recent discovery of gravitational waves and their connection to GRBs justifies a high-precision GRB polarimeter that can provide both highprecision polarimetry and detection of very faint GRBs. The POLAR-2 polarimeter is based on the same Compton scattering measurement principle as POLAR, but with an extended energy range and an order of magnitude increase in total effective area for polarized events. Proposed and developed by a joint effort of Switzerland, China, Poland and Germany, the device was selected for installation on the China Space Station and is scheduled to start operation for at least 2 years in 2025.

Energy-dependent polarization of Gamma-Ray Bursts' prompt emission with the POLAR and POLAR-2 instruments

“…One of the main outcome from the POLAR experiment except for its science results is the need for a next generation of more sensitive 𝛾-ray polarimeters in order to precisely measure time and energy resolved polarization. A bigger and more sensitive version of POLAR, called POLAR-2 [6][7][8], is therefore under development. A quick overview of this instrument will be given, while its sensitivity to energy dependence of polarization will be studied in a future paper [5].…”

“…The statistics being one of the main limiting factor for precisely measuring the polarization of GRBs, a bigger Compton polarimeter based on the legacy of POLAR is under development to be launched to the China Space Station in 2025 [6][7][8]. Called POLAR-2, this instrument will contain 4 times more channels, as depicted in the CAD model in Figure 6a.…”

ICRC 2023 Rapporteur: Status of the Gamma-ray Astronomy field

“…This energy range (also sub-MeV) is where phenomena like the Cosmic X-ray Background (CXB) or Gamma Ray Bursts (GRBs) are monitored. There were presentation of balloons like CXBe, the flexible X-ray detector focused on the CXB studies [1], POLAR-2, the next generation of GRB polarization detector that will be located in the Chinese Space Station (CSS) after the successful results of POLAR [2], the MoonBEAM cislunar SmallSat design [3] or XL-Calibur, a proposal for a balloon-borne X-ray polarimeter [4].…”