44 research outputs found
Construction and On-site Performance of the LHAASO WFCTA Camera
The focal plane camera is the core component of the Wide Field-of-view
Cherenkov/fluorescence Telescope Array (WFCTA) of the Large High-Altitude Air
Shower Observatory (LHAASO). Because of the capability of working under
moonlight without aging, silicon photomultipliers (SiPM) have been proven to be
not only an alternative but also an improvement to conventional photomultiplier
tubes (PMT) in this application. Eighteen SiPM-based cameras with square light
funnels have been built for WFCTA. The telescopes have collected more than 100
million cosmic ray events and preliminary results indicate that these cameras
are capable of working under moonlight. The characteristics of the light
funnels and SiPMs pose challenges (e.g. dynamic range, dark count rate,
assembly techniques). In this paper, we present the design features,
manufacturing techniques and performances of these cameras. Finally, the test
facilities, the test methods and results of SiPMs in the cameras are reported
here.Comment: 45 pages, 21 figures, articl
Measurement of ultra-high-energy diffuse gamma-ray emission of the Galactic plane from 10 TeV to 1 PeV with LHAASO-KM2A
The diffuse Galactic -ray emission, mainly produced via interactions
between cosmic rays and the interstellar medium and/or radiation field, is a
very important probe of the distribution, propagation, and interaction of
cosmic rays in the Milky Way. In this work we report the measurements of
diffuse -rays from the Galactic plane between 10 TeV and 1 PeV
energies, with the square kilometer array of the Large High Altitude Air Shower
Observatory (LHAASO). Diffuse emissions from the inner
(, ) and outer
(, ) Galactic plane are detected with
and significance, respectively. The outer Galactic
plane diffuse emission is detected for the first time in the very- to
ultra-high-energy domain (~TeV). The energy spectrum in the inner Galaxy
regions can be described by a power-law function with an index of
, which is different from the curved spectrum as expected from
hadronic interactions between locally measured cosmic rays and the
line-of-sight integrated gas content. Furthermore, the measured flux is higher
by a factor of than the prediction. A similar spectrum with an index of
is found in the outer Galaxy region, and the absolute flux for
TeV is again higher than the prediction for hadronic
cosmic ray interactions. The latitude distributions of the diffuse emission are
consistent with the gas distribution, while the longitude distributions show
clear deviation from the gas distribution. The LHAASO measurements imply that
either additional emission sources exist or cosmic ray intensities have spatial
variations.Comment: 12 pages, 8 figures, 5 tables; accepted for publication in Physical
Review Letters; source mask file provided as ancillary fil
Does or did the supernova remnant Cassiopeia A operate as a PeVatron?
For decades, supernova remnants (SNRs) have been considered the prime sources
of Galactic Cosmic rays (CRs). But whether SNRs can accelerate CR protons to
PeV energies and thus dominate CR flux up to the knee is currently under
intensive theoretical and phenomenological debate. The direct test of the
ability of SNRs to operate as CR PeVatrons can be provided by ultrahigh-energy
(UHE; ~TeV) -rays. In this context, the historical
SNR Cassiopeia A (Cas A) is considered one of the most promising target for UHE
observations. This paper presents the observation of Cas A and its vicinity by
the LHAASO KM2A detector. The exceptional sensitivity of LHAASO KM2A in the UHE
band, combined with the young age of Cas A, enabled us to derive stringent
model-independent limits on the energy budget of UHE protons and nuclei
accelerated by Cas A at any epoch after the explosion. The results challenge
the prevailing paradigm that Cas A-type SNRs are major suppliers of PeV CRs in
the Milky Way.Comment: 11 pages, 3 figures, Accepted by the APJ
Cosmic ray shower rate variations detected by the ARGO-YBJ experiment during thunderstorms
The ARGO-YBJ detector, located at the Yangbajing Cosmic Ray Laboratory (4300 m a. s. l., Tibet, China), was a "full coverage" air shower array. The high altitude location and the frequent occurrence of thunderstorms, made ARGO-YBJ suitable to study the effects of atmospheric electric fields (AEF) on secondary cosmic rays. By analyzing the data of the ARGO-YBJ detector recorded during thunderstorms, significant variations of the rate of detected showers have been observed. During 20 thunderstorm episodes in 2012, the variations of the shower rates (both increases and decreases of amplitudes up to a few percent) are found to be correlated to the intensity and polarity of the AEF, and strongly dependent on the primary zenith angle. To understand the observed behavior, Monte Carlo simulations have been performed with CORSIKA and G4argo (a code based on GEANT4). We found that the data are well consistent with simulations, assuming the presence of a uniform electric field in a layer of thickness of 500 m in the atmosphere above the observation level. Due to the AEF accelerates/decelerates and deflects the secondary charged particles (mainly electrons and positrons) according to their charge, modifying the number and position of particles with energy exceeding the detector threshold. For the differences in electron and positron flux, spectrum, and lateral distribution, the AEF has an asymmetric effect on the shower particles, producing significant variations of the particle pattern on the ground, and, consequently, on the rate of detected showers, consistent with observations
Cosmic ray shower rate variations detected by the ARGO-YBJ experiment during thunderstorms
The ARGO-YBJ detector, located at the Yangbajing Cosmic Ray Laboratory (4300 m a. s. l., Tibet, China), was a full coverageair shower array. The high altitude location and the frequent occurrence of thunderstorms, made ARGO-YBJ suitable to study the effects of atmospheric electric fields (AEF) on secondary cosmic rays. By analyzing the data of the ARGO-YBJ detector recorded during thunderstorms, significant variations of the rate of detected showers have been observed. During 20 thunderstorm episodes in 2012, the variations of the shower rates (both increases and decreases of amplitudes up to a few percent) are found to be correlated to the intensity and polarity of the AEF, and strongly dependent on the primary zenith angle. To understand the observed behavior, Monte Carlo simulations have been performed with corsika and g4argo (a code based on geant4). We found that the data are well consistent with simulations, assuming the presence of a uniform electric field in a layer of thickness of 500 m in the atmosphere above the observation level. Due to the AEF accelerates/decelerates and deflects the secondary charged particles (mainly electrons and positrons) according to their charge, modifying the number and position of particles with energy exceeding the detector threshold. For the differences in electron and positron flux, spectrum, and lateral distribution, the AEF has an asymmetric effect on the shower particles, producing significant variations of the particle pattern on the ground, and, consequently, on the rate of detected showers, consistent with observations
Extended Very-High-Energy Gamma-Ray Emission Surrounding PSR J0622+3749 Observed by LHAASO-KM2A
We report the discovery of an extended very-high-energy (VHE) gamma-ray source around the location of the middle-aged (207.8 kyr) pulsar PSR J0622 + 3749 with the Large High-Altitude Air Shower Observatory (LHAASO). The source is detected with a significance of 8.2 sigma for E > 25 TeV assuming a Gaussian template. The best-fit location is (right ascension, declination) = (95.47 degrees +/- 0.11 degrees, 37.92 degrees +/- 0.09 degrees), and the extension is 0.40 degrees +/- 0.07 degrees. The energy spectrum can be described by a power-law spectrum with an index of -2.92 +/- 0.17(st)(at) +/- 0.02(sys). No clear extended multiwavelength counterpart of the LHAASO source has been found from the radio to sub-TeV bands. The LHAASO observations arc consistent with the scenario that VHE electrons escaped from the pulsar, diffused in the interstellar medium, and scattered the interstellar radiation field. If interpreted as the pulsar halo scenario, the diffusion coefficient, inferred for electrons with median energies of similar to 160 TeV, is consistent with those obtained from the extended halos around Geminga and Monogem and much smaller than that derived from cosmic ray secondaries. The LHAASO discovery of this source thus likely enriches the class of so-called pulsar halos and confirms that high-energy particles generally diffuse very slowly in the disturbed medium around pulsars