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Doctoral thesis
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Development of the Next Generation Space-based Compton Polarimeter and Energy Resolved Polarization Analysis of Gamma-Ray Bursts Prompt Emission

Number of pages277
Imprimatur date2023
Defense date2023
Abstract

Discovered over half a century ago, Gamma-Ray Bursts (GRBs) are among the most powerful events in the universe since the Big Bang. They consist of a prompt gamma-ray emission followed by an afterglow spanning the entire electromagnetic spectrum. Two subpopulations of GRBs can be identified depending if their prompt emission lasts for more or less than 2 seconds. Short GRBs are originated from binary neutron star mergers while long ones are associated with the death of supermassive stars. Despite a few decades of spectral, temporal, and localization studies, the physics of these transient sources remains poorly understood. Polarization measurement of the prompt gamma-ray emission of GRBs is thought to be a powerful way to answer most of the open questions regarding the emission mechanism at play in these extragalactic sources, as well as the outflow dynamics and the jet and magnetic field structure.

With the intention to probe the physics of GRBs, a wide field-of-view dedicated GRB polarimeter sensitive in the 50-500 keV band, called POLAR, was sent to low Earth orbit together with the Tiangong-2 Chinese space lab in 2016. After 6 months of operation, it detected 55 GRBs, reporting low polarization levels for the 14 brightest for which enough statistics was gathered for polarization analysis. Two of these GRBs showed a hint for a time evolving polarization angle washing out the polarization degree on time-integrated analyses. The POLAR data analysis was taken even further in the frame of this thesis by studying the energy dependence of the polarization parameters measured for these GRBs. The energy-resolved analysis did not provide very constraining results as more statistics would be needed to provide significant energy-resolved polarization results of GRBs' prompt emission.

In order to bring high-quality GRB polarization measurements to the community, a new polarimeter based on the legacy of POLAR is therefore under development. This new generation polarimeter, POLAR-2, is 4 times bigger than its predecessor with an increase in sensitivity by an order of magnitude for typical GRB spectra. Planned for a launch to the China Space Station in 2025, the mission is expected to provide high-quality polarization measurements of about 50 GRBs per year. The design and development of the polarimeter modules as well as many space qualification tests were conducted in the frame of this thesis. The temperature dependence of thermal annealing of silicon photomultipliers was studied in detail in order to establish a strategy to counter the radiation damage effects that degrades the scientific performances of the sensors. A detailed Geant4 optical simulation, together with many optical characterization tests, was also performed in order to understand and optimize the light collection in the polarimeter modules.

This thesis first starts with an introductory part discussing our current understanding of GRBs and what polarization can teach us about these sources, as well as the state-of-the-art of high-energy polarimetry. The second part then summarizes the past achievements of the POLAR mission followed by a presentation of the energy-resolved polarization analysis conducted on the GRBs of the POLAR catalog. Finally, the third part describes the design and development of the POLAR-2 instrument, focusing on SiPM thermal annealing studies and optical characterization and simulation of the polarimeter modules.

eng
Keywords
  • Gamma-ray Bursts
  • Polarization
  • Polarimetry
  • SiPM
  • Silicon PhotoMultipliers
  • Optical simulation
  • Space
  • Radiation
Research group
Citation (ISO format)
DE ANGELIS, Nicolas. Development of the Next Generation Space-based Compton Polarimeter and Energy Resolved Polarization Analysis of Gamma-Ray Bursts Prompt Emission. 2023. doi: 10.13097/archive-ouverte/unige:173869
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Creation12/18/2023 10:59:09 AM
First validation12/19/2023 10:58:09 AM
Update time12/19/2023 10:58:09 AM
Status update12/19/2023 10:58:09 AM
Last indexation05/06/2024 5:37:53 PM
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