Speaker
Description
Gamma-Ray Bursts (GRBs) are among the most energetic events in the universe that have still open questions regarding their jet structure, magnetic-field geometry, and radiation mechanisms; polarization measurements are key to answering these questions. POLAR-2 is an improved version of its predecessor POLAR, and aims to measure the polarization of GRBs within a higher energy range of 30-800 KeV and with a much higher effective area thanks to its design. The instrument is constructed from 100 polarimeter modules each consisting of 8 × 8 array of rectangular plastic scintillator bars in which Compton-scattering events are reconstructed to measure the photon polarization. The scintillation light is read out using state-of-the-art silicon photomultipliers coupled through a novel optical interface which reduces the optical cross-talk between the scintillators. The interactions of the gamma-rays in the detector are simulated with Geant4, and the output of this simulation is passed to a digitization Monte Carlo (MC) to be converted to an ADC signal. An engineering qualification model (EQM), consisting of 3 × 3 polarimeter modules, is currently being assembled to validate and finalize the detector design. Moreover, a dedicated Module Analysis Framework has been developed to analyze calibration data, extract physical inputs for Geant4 modelling, and validate the simulation pipeline. To this effect, a major calibration campaign is scheduled for February 2026 at the European Synchrotron Radiation Facility (ESRF) to characterize the polarimetric response of the EQM. Upon completion of the EQM phase, POLAR-2 will proceed to full production and is scheduled for launch in early 2028 to China Space Station, where it will deliver unprecedented GRB polarisation measurements.
