Energy systematics and long term performance of the Pierre Auger Observatory’s fluorescence telescopes

Abstract

Since the discovery of cosmic rays in the early 20th century, physicists have strived to gain a deeper understanding of the properties behind the universe’s most energetic particles. Aiding in this effort has been the development and operation of very large cosmic ray detectors, which have successfully contributed to numerous advancements in the field of cosmic ray astrophysics. The most notable of such detectors is the Pierre Auger Observatory, situated in the Mendoza province of western Argentina, and is the result of an international effort to study cosmic rays of the highest of energies. The Pierre Auger Observatory utilises two well established methods to study enormous particle showers initiated by the interaction of incoming cosmic rays at the top of the Earth’s atmosphere. One such method is the detection of faint fluorescence light emitted during the longitudinal evolution of a cosmic ray initiated particle shower, achieved through the specially designed fluorescence detector. This thesis will investigate the long term performance and stability of the Pierre Auger Observatory’s energy scale, with a particular focus on the Observatory’s fluorescence detector. A brief history of the discovery of cosmic rays is presented in Chapter 1, followed by a discussion of the current knowledge of the properties of the cosmic ray flux and possible production mechanisms. Chapter 2 begins with a review of the physics of extensive air showers and shower detection methods, as well as a discussion of several notable cosmic ray experiments, both past and present. This is followed by an extensive discussion of the Pierre Auger Observatory in Chapter 3. Recent notable results and discoveries are highlighted in Chapter 4. Chapter 5 begins with a discussion of the calibration methods used to monitor the performance of the Observatory’s fluorescence detector. This will be followed by an extensive analysis of the long term stability of the Observatory’s energy scale. This includes a discussion of notable analyses improvements developed in recent years, and the effect of these improvements on the Observatory’s energy scale. Chapter 6 begins with a discussion of how the night sky background signal is monitored by the Observatory’s fluorescence detector. A cross check method is developed to use the night sky background observed between neighbouring fluorescence telescopes to monitor the stability of their inter-calibration. In Chapter 7 a cross check method is developed to monitor the long term stability of the fluorescence detector’s absolute calibration using stellar photometry. The results are compared with the long term stability of the Observatory’s energy scale from Chapter 5. The results from these studies are summarised in Chapter 8.