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Title: Calibration and analysis of the GCT camera for the Cherenkov Telescope Array
Author: Watson, Jason
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2018
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The interaction of very-high-energy astrophysical gamma rays with the Earth's atmosphere produces extensive electromagnetic particle cascades. These showers of particles travel faster than the speed of light in air, and consequently emit photons of blue wavelength, known as Cherenkov radiation. The Imaging Atmospheric Cherenkov Telescope (IACT) technique enables the probing of the universe at TeV energies through the detection of these Cherenkov showers. The Cherenkov Telescope Array (CTA) will represent the next leap forward in gamma-ray astronomy, improving on the sensitivity of current IACTs by a factor of 10, encompassing energies from 20 GeV to 300TeV, and operating as the first open observatory in this field. A major component of CTA is the Small-Sized Telescopes (SSTs), a necessary ingredient in exploring beyond the present energy frontier in gamma-ray astronomy. One of three proposed designs for the SST is the Gamma-ray Cherenkov Telescope (GCT). Utilising a dual-mirror Schwarzschild-Couder optical design, GCT enables a 9° Field of View (FoV) with a compact camera design. The camera developed for GCT is the Compact High Energy Camera (CHEC). Two prototypes for CHEC have been built, each utilising different compact photosensor technology. CHEC-M features Multi-Anode Photomultiplier Tubes (MAPMTs), a pixelised extension of the Photomultiplier Tube (PMT) technology extensively used by IACTs. CHEC-S features Silicon Photomultipliers (SiPMs), novel photosensors which utilise semiconductor technology for high-resolution photon counting over a large dynamic range. To fully utilise the signal output from these photosensors, and allow the opportunity for future data analysis procedures to be exploited, the signal received from these photosensors are digitised into waveforms following a trigger. These waveforms have a length of 96 samples with nanosecond precision. In this thesis, the full calibration and signal-extraction pipeline currently adopted by CHEC to reliably extract the Cherenkov signal from the waveforms is presented. The resulting performance of these procedures, and of the camera designs, is explored with respect to the requirements specified by the CTA Observatory. Potential improvements to the camera and calibration implementations are identified, and simulations of CHEC are utilised to demonstrate the performance increase these proposals provide. Consequently, an improvement to the photosensor that would allow the CHEC-S prototype design to comfortably meet the CTA requirements is specified. Testing of these improvements is anticipated to commence in early 2019. Finally, the results of the second on-telescope campaign for the CHEC-M prototype are presented, during which observations of Cherenkov showers and optical measurements of Jupiter were conducted.
Supervisor: Cotter, Garret Sponsor: Science and Technology Facilities Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Astrophysics