Development of Instrumentation and Methodology to Expand our View of Gamma-Ray Bursts: the Calibration of the BurstCube Instrument and a Methodology for Measuring Spectral Lags in Gamma-Ray Bursts with Multiple Emission Components
Open AccessThe first association of a Short Gamma-Ray Burst (SGRB) with a Gravitational Wave (GW) event proved that binary neutron star mergers (BNS) are the progenitors of at least a some SGRBs and propelled astronomy into a new multi-messenger era. Through this single detection, the multi-messenger community received new insight into fundamental physics, increased their knowledge of the nature of the SGRB/GW progenitors, and constrained cosmological parameters. However, many questions still remain such as; what is the geometry and nature of the relativistic jet? What is the composition of the relativistic outflow? What are the acceleration mechanisms? How does the jet propagate through the surrounding medium? What is the origin of the gamma-ray emission? To answer many of the remaining questions surrounding gamma-ray bursts (GRBs), additional joint detections with GWs are needed. This requires an increase in sky coverage in the gamma-ray regime in order to increase the likelihood of a joint detection. BurstCube, a 6U (10 cm x 20 cm x 30 cm) CubeSat, will expand sky coverage in order to detect, localize, and characterize GRBs. BurstCube is comprised of 4 Thallium doped Cesium Iodide (Cs(Tl)) scintillator crystals coupled to arrays of silicon photomultipliers (SiPMs) and is sensitive to gamma-rays between 50 keV and 1 MeV. The localization and spectrum of a GRB are derived from the energy and angular dependent instrument response, therefore, accurate ground based calibrations are required prior to launch. The main focus of this thesis is the calibration of the BurstCube instrument. The results from calibrations will then be used to benchmark simulations, from which the detector response matrices (DRMs) will be derived and the localizations and spectra of GRBs will be determined. While more SGRB/GW detections are needed, timing of the GRB prompt emission is also crucial to address the nature of the emission and subsequently the physical processes intrinsic to the relativistic outflow. With a temporal resolution of 10 microseconds, BurstCube will allow for fine time-resolved spectral analysis and greater insight into the timing of the prompt emission. The second objective of this thesis focuses on developing a method for exploring the physical origin of the observed spectral lags in GRBs, which correspond to delays in the arrival time of photons as a function of their energy. I simultaneously studied the spectral lags and fine time-resolved spectra of GRB 120323A in order to identify the various emission processes, which may overlap in the prompt emission, and developed a method for deriving lags from individual emission components. This method allows for a more physical interpretation to be applied to spectral lag measurements which may inform on the physical processes and origin of the gamma-ray prompt emission.
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