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

Abstract

The Telescope Array (TA) is the largest cosmic ray detector in the Northern hemisphere. Initially designed to study ultra high energy cosmic rays of energies above $10^{18}$ eV. The Telescope Array Low-energy Extension (TALE) extends the sensitivity of TA down to $10^{15.6}$ eV. The original TA consists of three fluorescence detectors, viewing 3$^{\circ}$ to 31$^{\circ}$ in elevation each, and overlooking an array of scintillation counters. TALE adds additional fluorescence telescopes at the TA Middle Drum (MD) fluorescence detector site, and overlooking a graded infill array of counters. Together, TALE and MD see a combined sky coverage of 114$^{\circ}$ in azimuth and 3-59$^{\circ}$ in elevation. In this work, we present a first measurement of the energy spectrum made by the combined TALE and MD fluorescence detectors operating in monocular mode.