Abstract
The Telescope Array (TA) is an experiment to observe Ultra-High Energy Cosmic Rays (UHECRs). TA's recent results, the energy spectrum and anisotropy based on the 6-year surface array data, and the primary composition obtained from the shower maximum Xmax are reported. The spectrum demonstrates a clear dip and cutoff. The shape of the spectrum is well described by the energy loss of extra-galactic protons interacting with the cosmic microwave background (CMB). Above the cutoff, a medium-scale (20 degrees radius) flux enhancement was observed near the Ursa-Major. A chance probability of creating this hotspot from the isotropic flux is 4.0 sigma. The measured Xmax is consistent with the primary being proton or light nuclei for energies 10^18.2 eV - 10^19.2 eV.
Highlights
A cutoff of the cosmic ray energy spectrum around 1020 eV was suggested by Greisen, Zatsepin and Kuzmin (GZK) in 1966 [1] just after the discovery of the cosmic microwave background (CMB)
The Telescope Array (TA) Low Energy extension, TALE, is a hybrid addition to the TA installed next to the north Fluorescence Detectors (FDs) station of TA, FD(MD). It is composed of 10 additional FD telescopes refurbished from High Resolution FE (HiRes) observing the higher elevation of 31◦ −59◦ above the FoV of FD(MD)
We presented the energy spectrum and the anisotropy measured by TA using 6 years of SD data
Summary
A cutoff of the cosmic ray energy spectrum around 1020 eV was suggested by Greisen, Zatsepin and Kuzmin (GZK) in 1966 [1] just after the discovery of the cosmic microwave background (CMB). A new air fluorescence technique for measuring UHECRs was established by the Fly’s Eye (FE) and High Resolution FE (HiRes) [3, 4] by 2000 In this technique, the longitudinal development of air shower in the atmosphere was recorded by fast imaging telescopes, and the primary cosmic ray energy was determined by integrating the profile of the shower development. The Telescope Array (TA) employs an array of Surface Detectors (SDs) covering a large ground area of 700 km, together with a set of Fluorescence Detectors (FDs) overlooking the SD area [5, 6] It is installed in the West Desert of Utah, USA, and has been taking data since 2008. We report here the recent results from TA as of summer 2014
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