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Register a new user10-100 TeV cosmic ray anisotropy measured at Baksan EAS Carpet array
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Preliminary results of one year anisotropy measurement in the energy range 10^{13} -10^{14} eV as a function of energy are presented. The results are compared for two methods of data analysis: the standard one with meteo correction approach in use and another one so-called East minus West method. Amplitudes and phases of anisotropy for three median energies E = 25 TeV, E = 75 TeV and E = 120 TeV are reported. Brief consideration of amplitude-phase dependence of anisotropy on energy is expounded.
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We report the analysis of the $10-1000$ TeV large-scale sidereal anisotropy of Galactic cosmic rays (GCRs) with the data collected by the Tibet Air Shower Array from October, 1995 to February, 2010. In this analysis, we improve the energy estimate and extend the declination range down to $-30^{circ}$. We find that the anisotropy maps above 100 TeV are distinct from that at multi-TeV band. The so-called tail-in and loss-cone features identified at low energies get less significant and a new component appears at $sim100$ TeV. The spatial distribution of the GCR intensity with an excess (7.2$sigma$ pre-trial, 5.2$sigma$ post-trial) and a deficit ($-5.8sigma$ pre-trial) are observed in the 300 TeV anisotropy map, in a good agreement with IceCubes results at 400 TeV. Combining the Tibet results in the northern sky with IceCubes results in the southern sky, we establish a full-sky picture of the anisotropy in hundreds of TeV band. We further find that the amplitude of the first order anisotropy increases sharply above $sim100$ TeV, indicating a new component of the anisotropy. All these results may shed new light on understanding the origin and propagation of GCRs.
Low energy ground-based cosmic ray air shower experiments generally have energy threshold in the range of a few tens to a few hundreds of TeV. The shower observables are measured indirectly with an array of detectors. The atmospheric absorption of low energy secondaries limits their detection frequencies at the Earths surface. However, due to selection effects, a tiny fraction of low energy showers, which are produced in the lower atmosphere can reach the observational level. But, due to less information of shower observables, the reconstruction of these showers are arduous. Hence, it is believed that direct measurements by experiments aboard on satellites and balloon flights are more reliable at low energies. Despite having very small efficiency ($sim$0.1%) at low energies, the large acceptance ($sim$5 m$^2$sr) of GRAPES-3 experiment allows observing primary cosmic rays down below to $sim$1 TeV and opens up the possibility to measure primary energy spectrum spanning from a few TeV to beyond cosmic ray knee (up to 10$^{16}$ eV), covering five orders of magnitude. The GRAPES-3 energy threshold for primary protons through Monte Carlo simulations are calculated, which gives reasonably good agreement with data. Furthermore, the total efficiencies and acceptance are also calculated for protons primaries. The ability of GRAPES-3 experiment to cover such a broader energy range may provide a unique handle to bridge the energy spectrum between direct measurements at low energies and indirect measurements at ultra-high energies.
The Cherenkov Telescope Array (CTA) is the next generation observatory for very high energy gamma rays. The capability of the array to detect gamma-rays above 10 TeV is going to be achieved with a large number of Small Size Telescopes (SSTs) which will cover a large area. The subarray composed of SSTs has to compromise the number of telescopes (cost) and the large effective area. The separation between the telescopes has to be adjusted to achieve highest sensitivity with the smallest number of telescopes. On the other hand larger separation can worsen the energy threshold as well as the energy and angular resolutions. In our study we have investigated the optimal spacing between the telescopes of the SST array using an analytical approach and the concept of telescope cell consisting of four telescopes as well as Monte Carlo simulations of the sets of cells.
Carpet is an air-shower array at Baksan, Russia, equipped with a large-area muon detector, which makes it possible to separate primary photons from hadrons. We report first results of the search for primary photons with energies E>100 TeV. The experiments ongoing upgrade and future sensitivity are also discussed.
We develop a model anisotropy best-fitting to the two-dimensional sky-map of multi-TeV galactic cosmic ray (GCR) intensity observed with the Tibet III air shower (AS) array. By incorporating a pair of intensity excesses in the hydrogen deflection plane (HDP) suggested by Gurnett et al., together with the uni-directional and bi-directional flows for reproducing the observed global feature, this model successfully reproduces the observed sky-map including the skewed feature of the excess intensity from the heliotail direction, whose physical origin has long remained unknown. These additional excesses are modeled by a pair of the northern and southern Gaussian distributions, each placed ~50 degree away from the heliotail direction. The amplitude of the southern excess is as large as ~0.2 %, more than twice the amplitude of the northern excess. This implies that the Tibet AS experiment discovered for the first time a clear evidence of the significant modulation of GCR intensity in the heliotail and the asymmetric heliosphere.
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