Séminaires LLR

Gamma-Ray Burst Polarimetry with POLAR and POLAR-2

by Mr Merlin Kole (Université de Genève)

Europe/Paris
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Description

Gamma-Ray Bursts (GRBs) are the brightest electro-magnetic explosions in the Universe since the Big Bang. Despite over 50 years of research on these extreme phenomena, many open questions remain about their nature and the environments in which the emission takes place. Polarization measurements of the high-energy emission have long been theorized to be able to answer most of these questions. Such measurements are, however, extremely complex to perform due to the low sensitivity of the instruments employed, the large systematic errors stemming from instrumental effects, and the difficulties in the analysis itself. The POLAR detector was a dedicated GRB polarimeter developed by a Swiss, Chinese and Polish collaboration. The instrument was launched, together with the second Chinese Space Lab, the Tiangong-2, in September 2016 after which it took 6 months of scientific data. During this period POLAR detected. The overall picture we get from the analysis of this GRB sample is that the emission is lowly or fully unpolarized. There is however the the caveat that within single pulses there are strong hints of an evolving polarization angle which washes out the polarization degree when analyzing the full GRB. Although the POLAR results thereby exclude a large portion of the polarization parameter space, to fully probe GRB polarization a significantly more sensitive detector is required. Such a detector, called POLAR-2, was recently approved for launch in 2024 and is currently being developed. I will present an overview of the POLAR mission and its scientific measurement results. Additionally, I will present the POLAR-2 detector which will have a sensitivity 10 times larger than POLAR. I will describe both the instrument design and the scientific prospects of this mission in detail.