The energy spectrum of cosmic rays above 1017.2 eV measured by the fluorescence detectors of the Telescope Array experiment in seven years

Abstract

The Telescope Array (TA) experiment is the largest detector to observe ultrahigh-energy cosmic rays in the northern hemisphere. The fluorescence detectors at two stations of TA are newly constructed and have now completed seven years of steady operation. One advantage of monocular analysis of the fluorescence detectors is a lower energy threshold for cosmic rays than that of other techniques like stereoscopic observations or coincidences with the surface detector array, allowing the measurement of an energy spectrum covering three orders of magnitude in energy. Analyzing data collected during those seven years, we report the energy spectrum of cosmic rays covering a broad range of energies 2 above 10 17.2 eV measured by the fluorescence detectors and a comparison with previously published results.

Measurement of the cosmic ray spectrum and chemical composition in the 1015-1018 eV energy range

“…Other two faint features (a hardening slightly above 10 16 eV and a steepening around 10 17 eV) have been observed in the all particle spectrum. These features have been claimed by the KASCADEGrande experiment [18] and then confirmed by Ice Top [4], TUNKA-133 [1] and TALE [2]. The spectral shapes agree quite well, the differences in the corresponding energies are smaller than the systematic error due to the energy calibration.…”

“…3 All particle spectrum measurements Figure 1 shows a summary [1,2,4,11,[14][15][16][17][18][19][20][21] of the all particle spectrum measurement. In this plot the results obtained by different experiments, operating at different heights above sea level, with different techniques and using different hadronic interaction models for the absolute energy calibration, have been collected.…”

“…Experiments studying primary cosmic rays in the 10 15 −10 18 eV energy range are ground based arrays, typical active surface ∼ 4 × 10 4 m 2 < Σ < 10 6 m 2 , detecting either the Cherenkov light emitted during Extensive Air Showers (EAS) development (TUNKA-133 [1], TALE [2]) either the electromagnetic and muon EAS components (KASCADE-Grande [3], Ice Top [4]). Pros and cons of both techniques are well known and can be briefly summarized: Cherenkov arrays are limited by statistical problems (their duty cycle being ∼ 10 − 15%) but can detect the light emitted during the whole shower development, thus performing an almost calorimetric measurement of the primary energy and are sensible to the depth of the shower maximum.…”

Search for EeV Protons of Galactic Origin

“…Figure 1d shows the model prediction for the galactic protons with energies distributed according to the measured spectrum of cosmic rays in the 10 18.0 − 10 18.5 eV range, [11,12,13,14,15,16,17], where the High Resolution Fly's Eye, Telescope Array, and Pierre Auger experiments are in good agreement, when their measurements are adjusted to use a common energy scale. Figure 1a shows the sky map if the distribution were isotropic.…”

First results from the full-scale prototype for the Fluorescence detector Array of Single-pixel Telescopes

“…Figure 6(a)(b) are two of the UHECR events observed with the new FAST prototype. The reconstructed energies from the TA FD monocular analysis [11] are 10 18.08 eV at an impact parameter R p = 2.4 km and 10 18.55 eV at R p = 3.0 km respectively. …”