This paper reports on the observation of the sidereal large-scale anisotropy of cosmic rays using data collected by the ARGO-YBJ experiment over 5 years (2008-2012). This analysis extends previous ...work limited to the period from 2008 January to 2009 December, near the minimum of solar activity between cycles 23 and 24. With the new data sample, the period of solar cycle 24 from near minimum to maximum is investigated. A new method is used to improve the energy reconstruction, allowing us to cover a much wider energy range, from 4 to 520 TeV. Below 100 TeV, the anisotropy is dominated by two wide regions, the so-called "tail-in" and "loss-cone" features. At higher energies, a dramatic change of the morphology is confirmed. The yearly time dependence of the anisotropy is investigated. Finally, no noticeable variation of cosmic-ray anisotropy with solar activity is observed for a median energy of 7 TeV.
We report on 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 1995 October to 2010 February. ...In this analysis, we improve the energy estimate and extend the decl. range down to −30°. We find that the anisotropy maps above 100 TeV are distinct from that at a 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 ∼100 TeV. The spatial distribution of the GCR intensity with an excess (7.2 pre-trial, 5.2 post-trial) and a deficit (−5.8 pre-trial) are observed in the 300 TeV anisotropy map, in close agreement with IceCube's results at 400 TeV. Combining the Tibet results in the northern sky with IceCube's 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 ∼100 TeV, indicating a new component of the anisotropy. All these results may shed new light on understanding the origin and propagation of GCRs.
Abstract
GRANDProto35 is the first stage of the GRAND project. It will be composed of an array of 35 radio antennas and 24 scintillation detectors in which the radio and scintillating subarrays will ...be triggered independently. The scintillation detector array allows to cross-check the radio array, thus quantitatively determine its detection efficiency. The photomultiplier of Hamamatsu R7725 is a candidate for the scintillation detector. The characteristics of the PMT will directly affect the resolution of the time and energy measurements and the dynamic detection range of a scintillation detector. A voltage divider circuit featured with dual-readout was designed for the PMT to cover a larger linear dynamic range (LDR). Some characteristics of the PMT were calibrated and investigated: the absolute gain, single photoelectron (SPE) energy resolution, transit time spread (TTS), linear dynamic range, and temperature dependence of the PMT gain. In this paper, details about the system setup, measurement methods, and results will be described.
The hadronic interaction of cosmic rays with solar atmosphere can produce high energy gamma-rays. The gamma-ray luminosity is correlated both with the flux of primary cosmic rays and the intensity of ...the solar magnetic field. The gamma-rays below 200 GeV have been observed by Fermi without any evident energy cutoff. The bright gamma-ray flux above 100 GeV has been detected only during solar minimum. The only available data in the TeV range come from the HAWC observations, however, outside the solar minimum. The ARGO-YBJ data set has been used to search for sub-TeV/TeV gamma-rays from the Sun during the solar minimum from 2008 to 2010, the same time period covered by the Fermi data. A suitable model containing the Sun shadow, solar disk emission, and inverse-Compton emission has been developed, and the chi-square minimization method was used to quantitatively estimate the disk gamma-ray signal. The result shows that no significant gamma-ray signal is detected and upper limits to the gamma-ray flux at 0.3-7 TeV are set at the 95% confidence level. In the low energy range these limits are consistent with the extrapolation of the Fermi-LAT measurements taken during solar minimum and are compatible with a softening of the gamma-ray spectrum below 1 TeV. They also provide an experimental upper bound to any solar disk emission at TeV energies. Models of dark matter annihilation via long-lived mediators predicting gamma-ray fluxes >10−7 GeV cm−2 s−1 below 1 TeV are ruled out by the ARGO-YBJ limits.
A wide field of view (FOV) is an important feature of a detector in the gamma ray observation of sporadic, extended, and transient sources. In this work, we discuss an atmospheric Cherenkov telescope ...(ACT) with a refractive water convex lens as its light collector, and we test the feasibility of this new approach. We determine the optical properties of a water lens with a diameter of 0.9 m, such as focal length, spot size, and transmittance. The first detection of cosmic rays (CRs) observed in coincidence with a scintillator extensive air shower (EAS) array is presented and discussed.
The hybrid Tibet AS array was successfully constructed in 2014. It has 4500 m2 underground water Cherenkov pools used as the muon detector (MD) and 789 scintillator detectors covering 36900 m2 as the ...surface array. At 100 TeV, cosmic-ray background events can be rejected by approximately 99.99%, according to the full Monte Carlo (MC) simulation for γ-ray observations. In order to use the muon detector efficiently, we propose to extend the surface array area to 72900 m2 by adding 120 scintillator detectors around the current array to increase the effective detection area. A new prototype scintillator detector is developed via optimizing the detector geometry and its optical surface, by selecting the reflective material and adopting dynode readout. {This detector can meet our physics requirements with a positional non-uniformity of the output charge within 10% (with reference to the center of the scintillator), time resolution FWHM of ∼2.2 ns, and dynamic range from 1 to 500 minimum ionization particles}.
Externally generated, axial magnetic fields used to confine high-current plasma beams in compact linear devices are usually 0.5 Tesla or less and can be insufficient to suppress plasma instabilities. ...Such an issue is addressed in this study by closely winding the current-carrying cable around a small chamber attached to the end of a linear device. The magnetic field generated inside the small chamber during the high-current pulse reached 0.8 Tesla at the peak current of 10.83 kA. Formation of a steady plasma beam through a mixture of argon, hydrogen and helium was photographed by a high-speed camera at the instant of the peak current. The beam width profile starts from over 24.8 mm at the upstream location and becomes thinner with distance down-stream. At the location of laser-interferometer measurement, at the right-most viewing window on the test chamber, the beam width was estimated as 7.4 mm and plasma density was evaluated to be 1.0 × 1022 m−3, an increase of two orders of magnitude compared to a previous study. A simple relationship was derived for the plasma density as a function of beam width. Based on examination of the metal target at the far end, the final beam width was estimated as 50 µm, with the plasma density evaluated to be 4.31 × 1022 m−3, with a calculated ion energy of 4.35 keV, consistent with x-ray spectrum measurements.
The extension of the cosmic-ray spectrum beyond 1 petaelectronvolt (PeV; 10
electronvolts) indicates the existence of the so-called PeVatrons-cosmic-ray factories that accelerate particles to PeV ...energies. We need to locate and identify such objects to find the origin of Galactic cosmic rays
. The principal signature of both electron and proton PeVatrons is ultrahigh-energy (exceeding 100 TeV) γ radiation. Evidence of the presence of a proton PeVatron has been found in the Galactic Centre, according to the detection of a hard-spectrum radiation extending to 0.04 PeV (ref.
). Although γ-rays with energies slightly higher than 0.1 PeV have been reported from a few objects in the Galactic plane
, unbiased identification and in-depth exploration of PeVatrons requires detection of γ-rays with energies well above 0.1 PeV. Here we report the detection of more than 530 photons at energies above 100 teraelectronvolts and up to 1.4 PeV from 12 ultrahigh-energy γ-ray sources with a statistical significance greater than seven standard deviations. Despite having several potential counterparts in their proximity, including pulsar wind nebulae, supernova remnants and star-forming regions, the PeVatrons responsible for the ultrahigh-energy γ-rays have not yet been firmly localized and identified (except for the Crab Nebula), leaving open the origin of these extreme accelerators.
The previously developed governing equations for Magnetic Inertial Confinement Fusion, which combines the advantages of both magnetic and inertial confinement approaches, are improved to analyse a ...plasma beam in a linear device assisted by an external magnetic field. The equations are applied to simulate a steady state plasma beam sustained by a DC power supply as well as a transient beam generated by a separate pulsed discharge superimposed on the steady-state plasma. The calculated increase of plasma density during the pulse from the steady-state condition is compared with measurements using a laser interferometer at a relatively low voltage supply of 150 V for the pulses. The numerical and test results are found to agree within 20%. When the voltage rises, plasma instability is observed. This issue is inherent due to the use of a solid positive target electrode that blocks the plasma flow in the axial direction. As a remedy, additional tests were carried out using a hollow target electrode in a two-circuit design (to permit free gas flow in the axial direction) by replacing the DC power with transient, pulsed, high-voltage sources for plasma initiation and beam formation. These enhancements were successful in suppressing the instabilities. The peak plasma density was calculated at ∼1022 m−3 for confinement times of the order of 1 ms. These results lie between the extremes for the current leading approaches yet are achieved for a more compact and inexpensive linear device.
Some gamma-ray bursts (GRBs) have a tera-electron volt (TeV) afterglow, but the early onset of this has not been observed. We report observations with the Large High Altitude Air Shower Observatory ...(LHAASO) of the bright GRB 221009A, which serendipitously occurred within the instrument's field of view. More than 64,000 photons >0.2 TeV were detected within the first 3000 seconds. The TeV flux began several minutes after the GRB trigger and then rose to a peak ~10 seconds later. This was followed by a decay phase, which became more rapid ~650 seconds after the peak. We interpret the emission using a model of a relativistic jet with half-opening angle of ~0.8°. This is consistent with the core of a structured jet and could explain the high isotropic energy of this GRB.
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