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Opis: Imaging Atmospheric Cherenkov Telescope (IACT) systems are used in high-energy astrophysics to detect and study gamma-ray sources in the universe. These telescopes measure properties of cosmic gamma rays using Cherenkov radiation emitted by secondary particles produced after interacting with the Earth’s atmosphere. Atmospheric monitoring is crucial for the proper operation of IACT systems. A number of remote sensing and in situ methods are used to understand and correct the effects of the atmosphere on the propagation of Cherenkov radiation from its origin to the telescope. Failure to do so greatly decreases IACT performance, particularly, their energy resolution and threshold. Lidar systems can be used to measure atmospheric optical depth profiles, which are essential for IACT calibration. The main aim of this thesis is to demonstrate that a prototype lidar for the north-ern site of the Cherenkov Telescope Array Observatory (CTAO), which is a next-generation IACT now under construction, has hardware and software capabilities that would lead to the construction of CTAO Raman lidar. Due to specific require-ments of the CTAO, a Raman lidar, which can provide better atmospheric parameter accuracy, will be used for the first time in an IACT system. In 2021-2022 the BRL was deployed to the future CTAO-North site at the Roque de los Muchachos observatory, La Palma, for testing in its actual operating conditions. During a year and a half long test period, it underwent a number of tests, including manual and remote operation under various environmental conditions. These included hot summers, cold winters, rain, snow, ice, and strong winds, but also some more exotic events, such as desert sand intrusions (Calima) and volcanic eruptions. The latter two are presented in this work as test cases for atmospheric characterization. Since the main goal of a CTAO lidar is the optical depth measurements, the BRL does not have the full set of features for aerosol characterization. While it can yield the ˚Angstr¨om exponent and lidar ratio, it does not provide depolarization informa-tion, which is one of the key components for aerosol typing. As the atmosphere at La Palma was found to be more complex than initially anticipated, we present the benefits of including depolarization capability by using a conceptually similar Raman lidar system specifically designed for aerosol characterization. We present the results of a campaign focused on the determination of bioaerosol capabilities to act as cloud condensation nuclei and ice-nucleating particles in mixed-phase clouds, where depo-larization information was used to determine the thermodynamic phase of the cloud.
Ključne besede: Cherenkov Telescope Array Observatory, Raman Lidar, atmospheric optical depth, aerosol characterization, Cumbre Vieja, Calima
Objavljeno v RUNG: 23.10.2023; Ogledov: 881; Prenosov: 26
Celotno besedilo (26,88 MB)

Opis: The Telescope Array (TA) is the largest ultra-high energy cosmic ray (UHECR) observatory in the Northern Hemisphere. Together with the TA Low Energy Extension (TALE), TA×4, and TALE infill detector, the TA measures the properties of UHECR-induced extensive air showers (EAS) in the energy region from 10^15 eV to over 10^20 eV. Each of these uses a hybrid system with an array of scintillators to sample the footprint of the EAS at the Earth’s surface along with telescopes that measure the fluorescence and Cherenkov light from the EAS. The statistics at the highest energies are being enhanced with the TA×4 detector, half completed but still under construction, which will quadruple the surface detector area with telescopes. The TALE infill surface detectors were recently deployed to further lower the hybrid energy threshold of TALE. We present the status of the experiment and recent results on the energy spectrum, mass composition, and anisotropy, including new features in the energy spectrum at about 10^19.2 eV and in the UHECR arrival direction anisotropy.
Ključne besede: Telescope Array, TALE, low energy extension, TAx4, indirect detection, hybrid detection, ground array, surface detection, fluorescence detection, cerenkov light, ultra-high energy, cosmic rays, energy spectrum, composition, anisotropy
Objavljeno v RUNG: 10.10.2023; Ogledov: 776; Prenosov: 6
Celotno besedilo (26,81 MB)
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Opis: The TA experiment uses fluorescence telescopes to observe cosmic ray air showers. The telescope camera uses PMTs as Pixels. The telescope’s PMT pointing direction has an uncertainty of 0.1°, and more precise measurements of the telescope's optical properties are needed to more accurately reconstruct the cosmic ray air showers. We have developed the Opt-copter which is a light source mounted on a drone that can be flown within the telescope's field of view. Observational experiments with the Opt-copter have provided a more accurate analysis of the telescope viewing direction. In this study, we estimate the effect of this measurement of accurate telescope viewing direction on the reconstruction of cosmic ray air showers.
Ključne besede: Telescope Array, indirect detection, fluorescence detection, ultra-high energy, cosmic rays, composition, calibration, Xmax
Objavljeno v RUNG: 10.10.2023; Ogledov: 849; Prenosov: 6
Celotno besedilo (670,84 KB)
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Opis: The TAx4 experiment plans to realize an Ultra High Energy Cosmic Rays (UHECR) detection area four times larger than that of the TA experiment. TAx4 will include five hundreds new surface detectors (SD) spaced at 2.08 km and two new fluorescence detectors (FD), which provides hybrid observation of UHECRs. We deployed 257 SDs in 2019 and completed building 2 FD stations in 2020, all operating stably. The data acquisition of the SDs is made via six communication towers, and inter-tower triggers have been recently implemented.
Ključne besede: Telescope Array, TAx4, indirect detection, hybrid detection
Objavljeno v RUNG: 10.10.2023; Ogledov: 753; Prenosov: 6
Celotno besedilo (2,39 MB)
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Opis: This work presents observations of the optical emission of a lightning flash in conjunction with a downward-directed Terrestrial Gamma-ray Flash (TGF) at the Telescope Array detector. Previously in ICRC-2021, we reported joint observations by the Telescope Array Surface Detector (TASD), the Lightning Mapping Array, a sferic sensor, and a broadband interferometer of particle showers in coincidence with lightning. These observations consisted of energetic showers of approximately less than 10-microsecond duration with footprints on the ground of 3-6 kilometers in diameter, originating in the first one to two milliseconds of downward lightning leaders and in coincidence with the initial breakdown pulses stage of negative cloud-to-ground lighting leaders. Scintillator waveform and simulation studies confirmed that these showers must consist primarily of gamma radiations. In this work, we use the TASD detector, together with a high-speed video camera, in conjunction with multiple lightning instruments at the TASD site, to report on the optical emission associated with a downward-directed terrestrial gamma-ray flash. Results from this study allow us to further the understanding of the initiation and propagation mechanism of terrestrial gamma-ray flashes. It will also further our ability to compare the most recent satellite optical emissions counterpart of upward-directed TGFs to that of downward-directed TGFs.
Ključne besede: Telescope Array, low energy extension, indirect detection, hybrid detection
Objavljeno v RUNG: 10.10.2023; Ogledov: 751; Prenosov: 5
Celotno besedilo (2,91 MB)
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