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Neutron monitors (NMs) are large ground-based detectors of atmospheric secondary particles, mostly neutrons, from primary cosmic rays. Their sky direction and rigidity imply a well-defined incoming (asymptotic) direction in space. From 2015 December 16 to 2017 January 8, 6 of the 18 NM counters had been transferred from McMurdo to Jang Bogo, both in Antarctica, so data from similar detectors were recorded simultaneously at these two nearby NM stations. Autocorrelations of these NM count rates are well fit as the sum of three components: an exponential function and a cosine with a period of 1 day, both centered at zero lag, plus a constant. Fitting the cross correlation of the two count rates, the functions are no longer centered at zero lag. The best-fit cosine phase is at time lag −160.22 ± 0.12 minutes. Calculating cosmic-ray trajectories in Earth's magnetic field throughout the time interval, the mean difference in response-weighted asymptotic longitudes corresponds to time lag −169.41 ± 0.31 minutes, in close agreement with the observed lag. Thus, the cosine term is consistent with and provides a technique to cleanly measure the cosmic-ray anisotropy. In contrast, the peak term shows a time lag of –14.55 minutes, much closer to the –9.60 minutes lag in rotation due to the difference in geographic longitude. We find a similar behavior in the correlations between other pairs of stations. We propose that rapid fluctuations in the counting rate may be primarily due to cosmic-ray particles of very high energy.

Gamma rays from HESS J1849−000, a middle-aged TeV pulsar wind nebula (PWN), are observed by the Tibet air shower array and the muon detector array. The detection significance of gamma rays reaches 4.0 σ and 4.4 σ levels above 25 TeV and 100 TeV, respectively, in units of the Gaussian standard deviation σ . The energy spectrum measured between 40 TeV < E < 320 TeV for the first time is described with a simple power-law function of ${dN}/{dE}={(2.86\pm 1.44)\times {10}^{-16}(E/40\,\mathrm{TeV})}^{-2.24\pm 0.41}\,{\mathrm{TeV}}^{-1}\,{\mathrm{cm}}^{-2}\,{{\rm{s}}}^{-1}$ . The gamma-ray energy spectrum from the sub-TeV ( E < 1 TeV) to sub-PeV (100 TeV < E < 1 PeV) ranges, including the results of previous studies, can be modeled with the leptonic scenario, i.e., inverse Compton scattering by high-energy electrons accelerated by the PWN of PSR J1849−0001. On the other hand, the gamma-ray energy spectrum can also be modeled with the hadronic scenario in which gamma rays are generated from the decay of neutral pions produced by collisions between accelerated cosmic-ray protons and the ambient molecular cloud found in the gamma-ray-emitting region. The cutoff energy of cosmic-ray protons E _p,cut is estimated as ${\mathrm{log}}_{10}({E}_{{\rm{p}},\mathrm{cut}}/\mathrm{TeV})={3.73}_{-0.66}^{+2.98}$ , suggesting that protons are accelerated up to the PeV energy range. Our study thus proposes that HESS J1849−000 should be further investigated as a new candidate as a Galactic PeV cosmic-ray accelerator, or “PeVatron.”

A new air-shower core-detector array (YAC: Yangbajing air-shower Core-detector array) has been developed to measure the primary cosmic-ray composition at the ‘knee’ energies in Tibet, China, focusing mainly on the light components. The prototype experiment (YAC-I) consisting of 16 detectors has been constructed and operated at Yangbajing (4300 m a.s.l.) in Tibet since May 2009. YAC-I is installed in the Tibet-III AS array and operates together. In this paper, we performed a Monte Carlo simulation to check the sensitivity of the YAC-I+Tibet-III array to the cosmic-ray light component of cosmic rays around the knee energies, taking account of the observation conditions of the actual YAC-I+Tibet-III array. The selection of light component from others was made by use of an artificial neural network. The simulation shows that the light-component spectrum estimated by our methods can well reproduce the input ones within 10% error, and there will be about 30% systematic errors mostly induced by the primary and interaction models used. It is found that the full-scale YAC and the Tibet-III array is powerful to study the cosmic-ray composition, in particular, to obtain the energy spectra of protons and helium nuclei around the knee energies. [ABSTRACT FROM AUTHOR]