The Energy Spectrum of Ultra-High-Energy Cosmic Rays Measured by the Telescope Array FADC Fluorescence Detectors in Monocular Mode

TL;DR

This paper reports the measurement of the ultra-high-energy cosmic ray spectrum using Telescope Array's monocular fluorescence detectors, validating the spectrum with combined data and comparing it to previous measurements.

Contribution

It introduces a new measurement of the cosmic ray energy spectrum using FADC fluorescence detectors in monocular mode, including detailed simulation and validation methods.

Findings

The energy spectrum was successfully measured and merged from two detectors.

The combined spectrum agrees with previous surface detector results.

Validation of aperture calculation through data-simulation comparisons.

Abstract

We present a measurement of the energy spectrum of ultra-high-energy cosmic rays performed by the Telescope Array experiment using monocular observations from its two new FADC-based fluorescence detectors. After a short description of the experiment, we describe the data analysis and event reconstruction procedures. Since the aperture of the experiment must be calculated by Monte Carlo simulation, we describe this calculation and the comparisons of simulated and real data used to verify the validity of the aperture calculation. Finally, we present the energy spectrum calculated from the merged monocular data sets of the two FADC-based detectors, and also the combination of this merged spectrum with an independent, previously published monocular spectrum measurement performed by Telescope Array's third fluorescence detector (Abu-Zayyad {\it et al.}, {Astropart. Phys.} 39 (2012), 109). This combined spectrum corroborates the recently published Telescope Array surface detector spectrum (Abu-Zayyad {\it et al.}, {Astrophys. Journ.} 768 (2013), L1) with independent systematic uncertainties.