The Telescope Array (TA) observatory utilizes fluorescence detectors and surface detectors (SDs) to observe air showers produced by ultra high energy cosmic rays in Earth's atmosphere. Cosmic-ray ...events observed in this way are termed hybrid data. The depth of air shower maximum is related to the mass of the primary particle that generates the shower. This paper reports on shower maxima data collected over 8.5 yr using the Black Rock Mesa and Long Ridge fluorescence detectors in conjunction with the array of SDs. We compare the means and standard deviations of the observed X max distributions with Monte Carlo X max distributions of unmixed protons, helium, nitrogen, and iron, all generated using the QGSJet II-04 hadronic model. We also perform an unbinned maximum likelihood test of the observed data, which is subjected to variable systematic shifting of the data X max distributions to allow us to test the full distributions, and compare them to the Monte Carlo to see which elements are not compatible with the observed data. For all energy bins, QGSJet II-04 protons are found to be compatible with TA hybrid data at the 95% confidence level after some systematic X max shifting of the data. Three other QGSJet II-04 elements are found to be compatible using the same test procedure in an energy range limited to the highest energies where data statistics are sparse.
We report on a measurement of the cosmic ray energy spectrum by the Telescope Array Low-Energy Extension (TALE) air fluorescence detector (FD). The TALE air FD is also sensitive to the Cherenkov ...light produced by shower particles. Low-energy cosmic rays, in the PeV energy range, are detectable by TALE as Cherenkov events. Using these events, we measure the energy spectrum from a low energy of ∼2 PeV to an energy greater than 100 PeV. Above 100 PeV, TALE can detect cosmic rays using air fluorescence. This allows for the extension of the measurement to energies greater than a few EeV. In this paper, we describe the detector, explain the technique, and present results from a measurement of the spectrum using ∼1000 hr of observation. The observed spectrum shows a clear steepening near 1017.1 eV, along with an ankle-like structure at 1016.2 eV. These features present important constraints on the origin of galactic cosmic rays and on propagation models. The feature at 1017.1 eV may also mark the end of the galactic cosmic ray flux and the start of the transition to extragalactic sources.
Abstract
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
distributions of showers observed over this energy range. Data collected over a period of ∼4 yr were analyzed for this study. The resulting
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
, spanning the full range of the measured energies. We also examine the mean
value as a function of energy for cosmic rays with energies greater than 10
15.8
eV. Below 10
17.3
eV, the slope of the mean
as a function of energy (the elongation rate) for the data is significantly smaller than that of all elements in the models, indicating that the composition is becoming heavier with energy in this energy range. This is consistent with a rigidity-dependent cutoff of events from Galactic sources. Finally, an increase in the
elongation rate is observed at energies just above 10
17
eV, indicating another change in the cosmic-ray composition.
The Pierre Auger Collaboration (Auger) recently reported a correlation between the arrival directions of cosmic rays with energies above 39 EeV and the flux pattern of 23 nearby starburst galaxies ...(SBGs). In this Letter, we tested the same hypothesis using cosmic rays detected by the Telescope Array experiment (TA) in the 9 yr period from 2008 May to 2017 May. Unlike the Auger analysis, we did not optimize the parameter values but kept them fixed to the best-fit values found by Auger, namely 9.7% for the anisotropic fraction of cosmic rays assumed to originate from the SBGs in the list and 12 9 for the angular scale of the correlations. The energy threshold that we adopted is 43 EeV, corresponding to 39 EeV in Auger when taking into account the energy-scale difference between two experiments. We find that the TA data is compatible with isotropy to within 1.1 and with the Auger result to within 1.4 , meaning that it is not capable to discriminate between these two hypotheses.
Evidence for a large-scale supergalactic cosmic-ray multiplet (arrival directions correlated with energy) structure is reported for ultra-high-energy cosmic-ray (UHECR) energies above 1019 eV using 7 ...years of data from the Telescope Array (TA) surface detector and updated to 10 years. Previous energy-position correlation studies have made assumptions regarding magnetic field shapes and strength, and UHECR composition. Here the assumption tested is that, because the supergalactic plane is a fit to the average matter density of the local large-scale structure, UHECR sources and intervening extragalactic magnetic fields are correlated with this plane. This supergalactic deflection hypothesis is tested by the entire field-of-view (FOV) behavior of the strength of intermediate-scale energy-angle correlations. These multiplets are measured in spherical cap section bins (wedges) of the FOV to account for coherent and random magnetic fields. The structure found is consistent with supergalactic deflection, the previously published energy spectrum anisotropy results of the TA (the Hotspot and Coldspot), and toy-model simulations of a supergalactic magnetic sheet. The seven year data posttrial significance of this supergalactic structure of multiplets appearing by chance, on an isotropic sky, is found by Monte Carlo simulation to be 4.2 . The 10 years of data posttrial significance is 4.1 . Furthermore, the starburst galaxy M82 is shown to be a possible source of the TA Hotspot, and an estimate of the supergalactic magnetic field using UHECR measurements is presented.
•The burst of air shower like events related lightning discharge.•The spatial distribution of high energy radiation from lightning was observed.•The shower reconstruction shows that the shower was ...initiated at a low altitude.
The Telescope Array (TA) experiment is designed to detect air showers induced by ultra high energy cosmic rays. The TA ground Surface particle Detector (TASD) observed several short-time bursts of air shower like events. These bursts are not likely due to chance coincidence between single shower events. The expectation of chance coincidence is less than 10−4 for five-year's observation. We checked the correlation between these bursts of events and lightning data, and found evidence for correlations in timing and position. Some features of the burst events are similar to those of a normal cosmic ray air shower, and some are not. On this paper, we report the observed bursts of air shower like events and their correlation with lightning.
Motivated by the detection of a significant dipole structure in the arrival directions of ultra-high-energy cosmic rays above 8 EeV reported by the Pierre Auger Observatory (Auger), we search for a ...large-scale anisotropy using data collected with the surface detector array of the Telescope Array Experiment (TA). With 11 yr of TA data, a dipole structure in a projection of the R.A. is fitted with an amplitude of 3.3% 1.9% and a phase of 131° 33°. The corresponding 99% confidence-level upper limit on the amplitude is 7.3%. At the current level of statistics, the fitted result is compatible with both an isotropic distribution and the dipole structure reported by Auger.
ABSTRACT
The surface detector (SD) of the Telescope Array (TA) experiment allows us to detect indirectly photons with energies of the order of 1018 eV and higher, and to separate photons from the ...cosmic ray background. In this paper, we present the results of a blind search for point sources of ultra-high-energy (UHE) photons in the Northern sky using the TA SD data. The photon-induced extensive air showers are separated from the hadron-induced extensive air shower background by means of a multivariate classifier based upon 16 parameters that characterize the air shower events. No significant evidence for the photon point sources is found. The upper limits are set on the flux of photons from each particular direction in the sky within the TA field of view, according to the experiment’s angular resolution for photons. The average 95 per cent confidence level upper-limits for the point-source flux of photons with energies greater than 1018, 1018.5, 1019, 1019.5 and 1020 eV are 0.094, 0.029, 0.010, 0.0073 and 0.0058 km−2yr−1, respectively. For energies higher than 1018.5 eV, the photon point-source limits are set for the first time. Numerical results for each given direction in each energy range are provided as a supplement to this paper.
Bursts of gamma ray showers have been observed in coincidence with downward propagating negative leaders in lightning flashes by the Telescope Array Surface Detector (TASD). The TASD is a 700‐km2 ...cosmic ray observatory located in southwestern Utah, USA. In data collected between 2014 and 2016, correlated observations showing the structure and temporal development of three shower‐producing flashes were obtained with a 3‐D lightning mapping array, and electric field change measurements were obtained for an additional seven flashes, in both cases colocated with the TASD. National Lightning Detection Network information was also used throughout. The showers arrived in a sequence of 2–5 short‐duration (≤10 μs) bursts over time intervals of several hundred microseconds and originated at an altitude of ≃3–5 km above ground level during the first 1–2 ms of downward negative leader breakdown at the beginning of cloud‐to‐ground lightning flashes. The shower footprints, associated waveforms and the effect of atmospheric propagation indicate that the showers consist primarily of downward‐beamed gamma radiation. This has been supported by GEANT simulation studies, which indicate primary source fluxes of ≃1012–1014 photons for 16° half‐angle beams. We conclude that the showers are terrestrial gamma ray flashes, similar to those observed by satellites, but that the ground‐based observations are more representative of the temporal source activity and are also more sensitive than satellite observations, which detect only the most powerful terrestrial gamma ray flashes.
Key Points
Gamma ray showers have been detected in a surface scintillator array coincident with lightning observed by a lightning mapping array or Delta E antenna
The showers were produced less than 4–5 km above ground in the first 1–2 ms of downward negative breakdown during cloud‐to‐ground flashes
The source durations are better resolved than for satellite observations and are consistent with being produced by stepping of the initial leader breakdown
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