Design and Scientific Prospects of the POLAR-2 Mission

Merlin Kole; Nicolas De Angelis; Jiang He; Hongbang Liu; Jianchao Sun; Fei Xie; Jimmy Zaid

Abstract

The POLAR-2 mission consists of 3 instruments designed with the combined aim of producing a deeper understanding of Gamma-Ray Bursts. The mission will provide new insights regarding the geometries and emission mechanisms of the astrophysical jets which characterize these phenomena. To achieve this, POLAR-2 relies on polarization measurements and, for the first time will provide these using 2 separate polarimeter detectors. The first of these is a payload optimized to perform Compton polarimetry measurements in the 40–1000 keV energy range using a combination of plastic scintillators and silicon photo-multipliers. The development of this payload, the design of which is based on lessons learned from the POLAR mission, included optimization of plastic scintillator materials, their geometries and their wrapping. In addition, its development included detailed characterization, space qualification and radiation damage and mitigation strategies for the large number of silicon photo-multipliers included in the design. We will present these along with an overview of the readout electronics. These electronics were developed with flexibility in mind, as well as low cost and low power consumption. As such, its design is of interest beyond this polarimeter and is also used on the spectrometer instrument of POLAR-2 where it is used to read out an array of GAGG scintillators. This readout, in combination with a coded mask, allows this secondary instrument to provide detailed spectral measurements along with localization measurements of the observed gamma-ray bursts. The final instrument used in the mission aims to use gas-based detectors to perform polarization measurements in the keV energy region. The novelty of this design lies in its optimization for wide-field observations. In addition, it is specifically designed for transient source monitoring, capable of handling high fluxes, and its performance remains largely insensitive to rapid flux variations. The combination of the three instruments will allow to perform detailed spectral, localization and polarization measurements of these transient phenomena together for the first time. This paper will provide an overview of the technologies employed in the mission along with detailed predictions on its capabilities after its launch which is currently foreseen in 2027.

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