The Cosmic-Ray Composition between 2 PeV and 2 EeV Observed with the TALE Detector in Monocular Mode
We report on a measurement of the cosmic-ray composition by the Telescope Array Low-energy Extension (TALE) air fluorescence detector (FD). By making use of the Cherenkov light signal in addition to air fluorescence light from cosmic-ray (CR)-induced extensive air showers, the TALE FD can measure the properties of the cosmic rays with energies as low as ~2 PeV and exceeding 1 EeV. In this paper, we present results on the measurement of ${X}_{\max }$ distributions of showers observed over this energy range. Data collected over a period of ~4 yr were analyzed for this study. The resulting ${X}_{\max }$ distributions are compared to the Monte Carlo (MC) simulated data distributions for primary cosmic rays with varying composition and a four-component fit is performed. The comparison and fit are performed for energy bins, of width 0.1 or 0.2 in ${\mathrm{log}}_{10}(E/\mathrm{eV})$, spanning the full range of the measured energies. We also examine the mean ${X}_{\max }$ value as a function of energy for cosmic rays with energies greater than 1015.8 eV. Below 1017.3 eV, the slope of the mean ${X}_{\max }$ as a function of energy (the elongation rate) for the data is significantly smaller than that of all elements in the more »
Authors:
Award ID(s):
Publication Date:
NSF-PAR ID:
10230207
Journal Name:
The astrophysical journal
Volume:
909
Issue:
2
Page Range or eLocation-ID:
178
ISSN:
2041-8205
2. Abstract The hybrid design of the Pierre Auger Observatory allows for the measurement of the properties of extensive air showers initiated by ultra-high energy cosmic rays with unprecedented precision. By using an array of prototype underground muon detectors, we have performed the first direct measurement, by the Auger Collaboration, of the muon content of air showers between $$2\times 10^{17}$$ 2 × 10 17 and $$2\times 10^{18}$$ 2 × 10 18 eV. We have studied the energy evolution of the attenuation-corrected muon density, and compared it to predictions from air shower simulations. The observed densities are found to be larger thanmore »