The amplitude and phase of the cosmic-ray anisotropy are well established experimentally between 10 11 eV and 10 14 eV. The study of their evolution in the energy region 10 14-10 16 eV can provide a significant tool for the understanding of the steepening ("knee") of the primary spectrum. In this Letter, we extend the EAS-TOP measurement performed at E 0 ≈ 10 14 eV to higher energies by using the full data set (eight years of data taking). Results derived at about 10 14 and 4 × 10 14 eV are compared and discussed. Hints of increasing amplitude and change of phase above 10 14 eV are reported. The significance of the observation for the understanding of cosmic-ray propagation is discussed.

The extended TeV gamma-ray source ARGO J2031+4157 (or MGRO J2031+41) is positionally consistent with the Cygnus Cocoon discovered by Fermi-LAT at GeV energies in the Cygnus superbubble. Reanalyzing the ARGO-YBJ data collected from 2007 November to 2013 January, the angular extension and energy spectrum of ARGO J2031+4157 are evaluated. After subtracting the contribution of the overlapping TeV sources, the ARGO-YBJ excess map is fitted with a two-dimensional Gaussian function in a square region of 10 • × 10 • , finding a source extension σ ext = 1. • 8 ± 0. • 5. The observed differential energy spectrum is dN/dE = (2.5 ± 0.4) × 10 −11 (E/1 TeV) −2.6±0.3 photons cm −2 s −1 TeV −1 , in the energy range 0.2-10 TeV. The angular extension is consistent with that of the Cygnus Cocoon as measured by Fermi-LAT and the spectrum also shows a good connection with the one measured in the 1-100 GeV energy range. These features suggest to identify ARGO J2031+4157 as the counterpart of the Cygnus Cocoon at TeV energies. The Cygnus Cocoon, located in the star-forming region of Cygnus X, is interpreted as a cocoon of freshly accelerated cosmic rays related to the Cygnus superbubble. The spectral similarity with supernova remnants (SNRs) indicates that the particle acceleration inside a superbubble is similar to that in an SNR. The spectral measurements from 1 GeV to 10 TeV allows for the first time to determine the possible spectrum slope of the underlying particle distribution. A hadronic model is adopted to explain the spectral energy distribution.

A. S. 1)6Au=uIN(**), V. G. RYASSNY(**), 0. G. RYAZHSKAYA(**), 0. SAAVEDRA(*), V. P. TALQCHEIN(**), G. TRINCHERO(*), S. VERNE~TO(*), G. T. ZATSEPIN(**) and V. F. YAKUSHEV(**) (*) Istituto di C o s m o g w f e del C.N.R.

We present the analysis of the muon events with all muon multiplicities collected during 21804 hours of operation of the first LVD tower. The measured angular distribution of muon intensity has been converted to the 'depth -vertical intensity' relation in the depth range from 3 to 12 km w.e.. The analysis of this relation allowed to derive the power index, γ, of the primary all-nucleon spectrum: γ = 2.78 ± 0.05. The 'depth -vertical intensity' relation has been converted to standard rock and the comparison with the data of other experiments has been done. We present also the derived vertical muon spectrum at sea level.PACS numbers: 13.85.T, 96.40.T

The observation of the diffuse Galactic gamma ray flux is the most powerful tool to study cosmic rays in different regions of the Galaxy, because the energy and angular distributions of the photons encode information about the density and spectral shape of relativistic particles in the entire MilkyWay. An open problem of fundamental importance is whether cosmic rays in distant regions of the Milky Way have the same spectral shape observed at the Earth or not. If the spectral shape of protons and nuclei is equal in all the Galaxy, the dominant, hadronic component of the diffuse gamma ray flux must have an angular distribution that, after correcting for absorption effects, is energy independent. To study experimentally the validity of this factorization of the energy and angular dependence of the diffuse flux it is necessary to compare observations in a very broad energy range. The extension of the observations to energies Eγ 0.1-10 PeV is of great interest, because it allows the study of the cosmic ray spectra around the feature known as the "knee". The absorption probability for photons in this energy range is not negligible, and distorts the energy and angular distributions of the diffuse flux, therefore a precise calculation of the absorption effects is necessary for the interpretation of the data. In this work we present predictions of the diffuse gamma ray flux at very high energy, constructed under different hypothesis for the space dependence of the cosmic ray energy spectra, and discuss the potential of the observations for present and future detectors.PACS numbers: 98.35Gi,95.85Pw,95.85Ry * Electronic address: paolo.lipari@roma1.infn.it † Electronic address: vernetto@to.infn.it

Galactic gamma ray astronomy at very high energy (Eγ 30 TeV) is a vital tool in the study of the nonthermal universe. The interpretation of the observations in this energy region requires the precise modeling of the attenuation of photons due to pair production interactions (γγ → e + e − ) where the targets are the radiation fields present in interstellar space. For gamma rays with energy Eγ 300 TeV the attenuation is mostly due to the photons of the cosmic microwave background radiation. At lower energy the most important targets are infrared photons with wavelengths in the range λ ≃ 50-500 µm emitted by dust. The evaluation of the attenuation requires a good knowledge of the density, and energy and angular distributions of the target photons for all positions in the Galaxy. In this work we discuss a simple model for the infrared radiation that depends on only few parameters associated to the space and temperature distributions of the emitting dust. The model allows to compute with good accuracy the effects of absorption for any space and energy distribution of the diffuse Galactic gamma ray emission. The absorption probability due to the Galactic infrared radiation is maximum for Eγ ≃ 150 TeV, and can be as large as P abs ≃ 0.45 for distant sources on lines of sight that pass close to the Galactic center. The systematic uncertainties on the absorption probability are estimated as ∆P abs 0.08.

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The measurement of the cosmic ray energy spectrum, in particular for individual species of nuclei, is an important tool to investigate cosmic ray production and propagation mechanisms. The determination of the "knees" in the spectra of different species remains one of the main challenges in cosmic ray physics. In fact, experimental results are still conflicting. In this paper we report a measurement of the mixed proton and helium energy spectrum, obtained with the combined data of the ARGO-YBJ experiment and a wide field of view Cherenkov telescope, a prototype of the future LHAASO experiment. By means of a multiparameter technique, we have selected a high-purity proton plus helium sample. The reconstructed energy resolution is found to be about 25% throughout the investigated energy range from 100 TeV to 3 PeV, with a systematic uncertainty in the absolute energy scale of 9.7%. The found energy spectrum can be fitted with a broken power-law function, with a break at the energy E k ¼ 700 AE 230ðstatÞ AE 70ðsysÞ TeV, where the spectral * zhangss@ihep.ac.cn † caozh@ihep.ac.cn PHYSICAL REVIEW D 92, 092005 (2015) 1550-7998=2015=92(9)=092005 (12) 092005-1 © 2015 American Physical Society index changes from −2.56 AE 0.05 to −3.24 AE 0.36. The statistical significance of the observed spectral break is 4.2 standard deviations.