Advancing Gamma-ray Burst and MeV Science with Fermi and the Path Forward with AMEGO
Open Access DepositedFrom Data to Detection
Relativistic astrophysical jets are believed to host physical processes in some ofthe most extreme conditions, such as intense magnetic fields and high velocities. They are understood to accelerate particles close to the speed of light, generating highly energetic cosmic rays. These conditions are unobtainable on Earth, so we can use these jets as natural laboratories, allowing us to study physics at its limits. Gamma-ray bursts (GRBs) emit such relativistic jets. GRBs are the most ener- getic events in the universe. They are highly luminous explosions that occur in distant galaxies. These bursts either come from a binary compact object merger, or the death of a massive star. In both scenarios, a black hole central engine is formed, emitting a jet of collimated particles. The early flash of gamma-rays produced from these jets is called GRB prompt emission, which is mostly non-thermal and thought to be of synchrotron origin. The spectrum of this prompt emission has been historically hard to model, making the physics difficult to interpret. While the Band function, a type of smoothly-broken power law, has traditionally been used to fit the prompt emission spectrum, recent analysis found a discrepancy when fitting it to Fermi Gamma-ray Burst Monitor (GBM) data and Fermi Large Area Telescope (LAT) data. Recent studies, however, show the possible existence of multiple emission components in the keV regime, which could be key in resolving said discrepancy. These results can then be used to constrain the spectral energy distribution of electrons within GRB jets, offering another piece of information on the underlying acceleration mechanisms and physical conditions of the outflow. Therefore, the first objective of this thesis will focus on studying the curvature of the MeV spectra of GRBs, and the implications of the multi-component model. However, the spectrum of GRB prompt emission breaks in the MeV regime, where neither GBM nor LAT is sensitive. This necessitates the need for a mission in the medium energy gamma-ray range. The All-sky Medium Energy Gamma-ray Ob- servatory (AMEGO) and AMEGO explorer (AMEGO-X), will have capabilities to collect data in this complex region, with over 10 times the sensitivity of previous instruments. The ComPair balloon instrument, which flew in August 2023, is the prototype for AMEGO, and served as a technology demonstration in a space-like environment. ComPair is composed of four subsystems
a double-sided silicon strip detector (DSSD) Tracker, a virtual Frisch CZT Low Energy Calorimeter, a CsI High Energy Calorimeter, and an anti-coincidence detector (ACD) to reject charged parti- cle backgrounds. The second focus of this thesis will be on the development, calibra- tion, and performance of the DSSD Tracker as well as the entire ComPair instrument.
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