Abstract
The origin and nature of ultrahigh-energy cosmic rays (UHECRs) is one of the most intriguing and important mysteries in astroparticle physics. The two largest observatories currently in operation, the Telescope Array Experiment in central Utah, USA, and the Pierre Auger Observatory in western Argentina, have been steadily observing UHECRs in both hemispheres for over a decade. We highlight the latest results from both of these experiments, and address the requirements for a next-generation UHECR observatory. The Fluorescence detector Array of Single-pixel Telescopes (FAST) is a design concept for a next-generation UHECR observa-tory, addressing the requirements for a large-area, low-cost detector suitable for measuring the properties of the highest energy cosmic rays with an unprecedented aperture. We have developed a full-scale prototype consisting of four 200 mm photomultiplier-tubes at the focus of a segmented mirror of 1.6 m in diameter. Over the last three years, we installed three such prototypes at the Black Rock Mesa site of the Telescope Array Experiment. These telescopes have been steadily taking data since installation. We report on preliminary results of the full-scale FAST prototypes, including measurements of distant ultraviolet lasers and UHECRs. Futhermore, we discuss our plan to install an additional identical FAST prototype at the Pierre Auger Observatory. Possible benefits to the Telescope Array and the Pierre Auger Observatory include a comparison of the transparency of the atmosphere above both experiments, a study of the systematic uncertainty associated with their existing fluorescence detectors, and a cross-calibration of their energy and Xmax scales.
Highlights
Since ultrahigh-energy cosmic rays (UHECRs) are the most energetic particles in the universe, their origins are ostensibly related to extremely energetic astrophysical phenomena, such as gamma-ray bursts, active galactic nuclei, or other exotic processes such as the decay or annihilation of super-heavy relic particles created in an early phase of the development of the universe [1]
When a fluorescence telescope in the adjacent Telescope Array Experiment (TA) building is triggered by a candidate UHECR shower, an external trigger is issued to the Fluorescence detector Array of Single-pixel Telescopes (FAST) DAQ with a typical rate of ∼ 3 Hz
The telescope frames were assembled on site, before the photomultiplier tubes (PMTs) were mounted in the camera box and the UV band-pass filter was installed at the telescope aperture
Summary
Since ultrahigh-energy cosmic rays (UHECRs) are the most energetic particles in the universe, their origins are ostensibly related to extremely energetic astrophysical phenomena, such as gamma-ray bursts, active galactic nuclei, or other exotic processes such as the decay or annihilation of super-heavy relic particles created in an early phase of the development of the universe [1]. Their origin and acceleration mechanism above 1020 eV are still unknown. One in each hemisphere, the Pierre Auger Observatory (Auger) in Mendoza, Argentina [15] and the Telescope Array Experiment (TA) in Utah, USA [16, 17], combine the two techniques with arrays of particle detectors overlooked by fluorescence detectors (FD)
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