Ultra-high energy nuclei source in the direction to Virgo cluster

The significant anisotropy in the arrival directions of the 69 events with energy E> 55 EeV detected by Pierre Auger collaboration is located in the 20-degree region centered near Cen A. Not only the 2-point, but also the 3-point and 4-point autocorrelation functions are completely saturated by this region. Besides there is an deficit of events in the direction of Virgo cluster. If one assumes that the excess around Cen A is due to heavy nuclei shifted from Virgo, one can explain 20-degree scale of this anomaly. Also location of the highest energy event between the Cen A region and the Virgo cluster supports this idea. Magnitude and direction of the magnetic field is similar in this case to those expected for Galactic models. The existence of nuclei sources in the sky opens the road for a self-consistent description of Auger data.Comment: 4 pages, 3 figure

Gamma-Ray Constraints on Maximum Cosmogenic Neutrino Fluxes and UHECR Source Evolution Models

The dip model assumes that the ultra-high energy cosmic rays (UHECRs) above 10$^{18}$ eV consist exclusively of protons and is consistent with the spectrum and composition measure by HiRes. Here we present the range of cosmogenic neutrino fluxes in the dip-model which are compatible with a recent determination of the extragalactic very high energy (VHE) gamma-ray diffuse background derived from 2.5 years of Fermi/LAT data. We show that the largest fluxes predicted in the dip model would be detectable by IceCube in about 10 years of observation and are within the reach of a few years of observation with the ARA project. In the incomplete UHECR model in which protons are assumed to dominate only above 10$^{19}$ eV, the cosmogenic neutrino fluxes could be a factor of 2 or 3 larger. Any fraction of heavier nuclei in the UHECR at these energies would reduce the maximum cosmogenic neutrino fluxes. We also consider here special evolution models in which the UHECR sources are assumed to have the same evolution of either the star formation rate (SFR), or the gamma-ray burst (GRB) rate, or the active galactic nuclei (AGN) rate in the Universe and found that the last two are disfavored (and in the dip model rejected) by the new VHE gamma-ray background.Comment: 19 pages, 16 figures, JHEP3.cls needed to typese

Cosmic-ray spectrum in the local Galaxy

Aims. We study the spectral properties of the cosmic-ray spectrum in the interstellar medium within 1 kpc distance from the Sun. Methods. We used eight-year exposure data of molecular clouds of the Gould Belt obtained with the Fermi-LAT telescope to precisely measure the cosmic-ray spectrum at different locations in the local Galaxy. We compared this measurement with the direct measurements of the cosmic-ray flux in and around the solar system obtained by Voyager and AMS-02 or PAMELA. Results. We find that the average cosmic-ray spectrum in the local Galaxy in the 1–100 GeV range is well described by a broken power-law in rigidity with a low-energy slope of 2.33+0.06-0.08 and a break at 18+7-4 GV, with a slope change by 0.59 ± 0.11. This result is consistent with an earlier analysis of the γ-ray signal from the Gould Belt clouds based on a shorter exposure of Fermi-LAT and with a different event selection. The break at 10–20 GV is also consistent with the combined Voyager + AMS-02 measurements in/around the solar system. The slope of the spectrum below the break agrees with the slope of the average cosmic-ray spectrum in the inner part of the disk of the Milky Way that was previously derived from the Fermi-LAT γ-ray data. We conjecture that it is this slope of 2.33 and not the locally measured softer slope of 2.7–2.8 that is determined by the balance between a steady-state injection of cosmic rays with a power-law slope of 2–2.1 that is due to Fermi acceleration and the energy-dependent propagation of cosmic-ray particles through the turbulent interstellar magnetic field with a Kolmogorov turbulence spectrum. The approximation of a continuous-in-time injection of cosmic rays at a constant rate breaks down, which causes the softening of the spectrum at higher energies

Strong constraints on hadronic models of blazar activity from Fermi and IceCube stacking analysis

International audienceContext. High-energy emission from blazars is produced by electrons that are either accelerated directly, under the assumption of leptonic models of blazar activity, or produced in interactions of accelerated protons with matter and radiation fields, under the assumption of hadronic models. The hadronic models predict that γ-ray emission is accompanied by neutrino emission with comparable total energy. Aims. We derive constraints on the hadronic models of activity of blazars imposed by non-detection of neutrino flux from a population of γ-ray emitting blazars. Methods. We stacked the γ-ray and muon neutrino flux from 749 blazars situated in the declination strip above − 5°. Results. Non-detection of neutrino flux from the stacked blazar sample rules out the proton-induced cascade models in which the high-energy emission is powered by interactions of a shock-accelerated proton beam in the active galactic nucleus (AGN) jet with the ambient matter or radiation field of the black hole accretion disk. The result also remains valid for the case of interactions in the scattered radiation field in the broad line region. The IceCube constraint could be avoided if the spectrum of accelerated protons is sharply peaking in the ultra-high-energy cosmic ray range, as in the models of acceleration in the magnetic reconnection regions or in the vacuum gaps of black hole magnetospheres. Models based on these acceleration mechanisms are only consistent with the data if characteristic energies of accelerated protons are higher than 1019 eV. The constraint could also be avoided if the hadronic emission component of γ-ray flux is largely sub-dominant compared to the leptonic component and/or if it only appears during flaring activity episodes, which provide negligible contribution to the time-averaged source flux. Key words: galaxies: active / gamma rays: galaxies / neutrino

Cosmic-ray composition measurements and cosmic ray background-free γ\gamma-ray observations with Cherenkov telescopes

International audienceThe muon component of extensive air showers (EAS) initiated by cosmic-ray particles carries information on the primary particle identity. We show that the muon content of EAS could be measured in a broad energy range from 10–100 TeV up to ultra-high-energy cosmic-ray range using wide field-of-view imaging atmospheric Cherenkov telescopes observing strongly inclined or nearly horizontal EAS from the ground of from high altitude. Cherenkov emission from muons in such EAS forms a distinct component (halo or tail) of the EAS image in the telescope camera. We show that detection of the muon signal could be used to measure composition of the cosmic-ray spectrum in the energy ranges of the knee, the ankle and of the Galactic-to-extragalactic transition. It could also be used to veto the cosmic-ray background in gamma-ray observations. This technique provides a possibility for up to 2 orders of magnitude improvement of sensitivity for γ-ray flux in the energy band above 10 PeV, compared to KASCADE-Grande, and an order-of-magnitude improvement of sensitivity in the multi-EeV energy band, compared to Pierre Auger Observatory