The Cosmic Ray Energy Spectrum above 0.1 EeV measured by the Telescope Array and TALE Fluorescence Telescopes

The Telescope Array (TA), deployed in the desert of central Utah, is the largest hybrid cosmic ray detector in the Northern hemisphere. It was initially designed to observe ultra high energy cosmic rays with energies >10¹⁹ eV, TA has added an extension, known as the Telescope Array Low-energy Extension (TALE), to lower the experiment's energy threshold by installing high elevation angle telescopes and a dense graded array of surface detectors to the existing main array. It allows us to study cosmic rays in 10^15.3-10^18.3 eV energy range. The observatory now consists of 48 fluorescence telescopes and a graded array of 610 surface detectors spread over ~750 km². The fluorescence telescopes observe the longitudinal development of an extensive air shower induced by a cosmic ray, by detecting the scintillation light as the shower develops. Meanwhile, the array of surface detectors measures the lateral distribution of particles reaching the Earth's surface. With TALE extension, the TA Middle Drum site has a field of view 114° in azimuth and 3-59° in elevation. In this work, I will present a measurement of energy spectrum in the energy range of 10^17.2-10^19.0 eV using fluorescence data collected by the TA and TALE telescopes.