Ponente
Descripción
The origin and nature of cosmic rays remain one of the most intriguing unsolved problems in modern astrophysics, even more than a century after their discovery.
The Telescope Array (TA) is the largest cosmic ray observatory in the northern hemisphere, continuously observing ultra-high energy cosmic rays (E$>10^{18}\,$eV) with a hybrid detector composed of fluorescence detectors (FD) and a surface detector (SD) array.
To further enhance observational exposure above $10^{19}\,$eV, we have been extending the SD array by a factor of four since 2019 as part of the TAx4 project, aiming to provide higher statistics for the highest-energy cosmic rays and enabling detailed studies on the energy spectrum, anisotropy, and mass composition.
In addition to ultra-high energy observations, TA has constructed high-elevation FDs and dense SD arrays (the TA Low Energy Extension, TALE) to lower the energy threshold and probe the cosmic ray spectrum, mass composition, and anisotropy in the crucial transition region from galactic to extragalactic cosmic rays ($10^{15}$–$10^{18}\,$eV).
Recent upgrades, including an infill SD array, further enhance our sensitivity in the lower energy range, allowing for more precise studies of this transition.
In this contribution, we present an overview of recent results covering five orders of magnitude in energy, and briefly discuss observations in the low-energy region relevant to the transition from galactic to extragalactic cosmic rays.
