Abstract
The Telescope Array (TA) experiment has three fluorescence detector (FD) stations to measure fluorescence light emitted from extensive air showers, especially produced by Ultra High Energy ...Cosmic Rays(UHECRs). These fluorescence light is attenuated and decreased by aerosols in the atmosphere during their propagation to the FD. Measuring and calibrating the atmospheric attenuation is necessary to estimate energy of primary cosmic rays. The central Laser Facility (CLF) consists of a laser of wavelength of 355 nm, and emits beam vertically with 10 Hz, every half-hour. The atmospheric transparency in terms of the Vertical Atmospheric Optical Depth (VAOD) is measured with the CLF every 30 minutes during FD observation. The CLF is located at the center of three FD stations and observes the atmospheric transparency of the TA site. We calculated VAOD
τ
AS
(5km) at the BR station using 1853 events of the CLF laser from January 2012 to September 2016. We found that the median of VAOD at 5 km height from the ground is
0.043
−
0.015
+
0.025
. We also found a seasonal variation of VAOD using the same data.
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.
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.
In this paper, we present the first high-speed video observation of a cloud-to-ground lightning flash and its associated downward-directed Terrestrial Gamma-ray Flash (TGF). The optical emission of ...the event was observed by a high-speed video camera running at 40,000 frames per second in conjunction with the Telescope Array Surface Detector, Lightning Mapping Array, interferometer, electric-field fast antenna, and the National Lightning Detection Network. The cloud-to-ground flash associated with the observed TGF was formed by a fast downward leader followed by a very intense return stroke peak current of -154 kA. The TGF occurred while the downward leader was below cloud base, and even when it was halfway in its propagation to ground. The suite of gamma-ray and lightning instruments, timing resolution, and source proximity offer us detailed information and therefore a unique look at the TGF phenomena.
Telescope Array (TA) is the largest ultrahigh energy cosmic-ray (UHECR) observatory in the Northern Hemisphere. It explores the origin of UHECRs by measuring their energy spectrum, arrival-direction ...distribution, and mass composition using a surface detector (SD) array covering approximately 700 km\(^2\) and fluorescence detector (FD) stations. TA has found evidence for a cluster of cosmic rays with energies greater than 57 EeV. In order to confirm this evidence with more data, it is necessary to increase the data collection rate.We have begun building an expansion of TA that we call TAx4. In this paper, we explain the motivation, design, technical features, and expected performance of the TAx4 SD. We also present TAx4's current status and examples of the data that have already been collected.
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