Using the analytic modeling of the electromagnetic cascades compared with more precise numerical simulations, we describe the physical properties of electromagnetic cascades developing in the ...universe on cosmic microwave background and extragalactic background light radiations. A cascade is initiated by very-high-energy photon or electron, and the remnant photons at large distance have two-component energy spectrum, proportional, variantE super(-2)(pro portional, variantE super(-1.9) in numerical simulations) produced at the cascade multiplication stage and proportional, variantE super(-3/2) from Inverse Compton electron cooling at low energies. The most noticeable property of the cascade spectrum in analytic modeling is "strong universality," which includes the standard energy spectrum and the energy density of the cascade omega sub(cas) as its only numerical parameter. Using numerical simulations of the cascade spectrum and comparing it with recent Fermi LAT spectrum, we obtained the upper limit on omega sub(cas) stronger than in previous works. The new feature of the analysis is the "E sub(max) rule." We investigate the dependence of omega sub(cas) on the distribution of sources, distinguishing two cases of universality: the strong and weak ones.
We consider decaying dark matter with masses 107≲M≲1016 GeV as a source of ultrahigh energy (UHE) gamma rays. Using recent limits on UHE gamma-ray flux for energies Eγ>2×1014 eV, provided by ...extensive air shower observatories, we put limits on masses and lifetimes of the dark matter. We also discuss possible dark matter decay origin of tentative 100 PeV photon flux detected with the EAS-MSU experiment.
An isotropic component of high energy γ-ray spectrum measured by Fermi LAT constrains the proton component of UHECR. The strongest restriction comes from the highest, (580−820) GeV, energy bin. One ...more constraint on the proton component is provided by the IceCube upper bound on ultrahigh energy cosmogenic neutrino flux. We study the influence of these restrictions on the source properties, such as evolution and distribution of sources, their energy spectrum and admixture of nuclei. We also study the sensitivity of restrictions to various Fermi LAT galactic foreground models (model B being less restrictive), to the choice of extragalactic background light model and to overall normalization of the energy spectrum. We claim that the γ-ray-cascade constraints are stronger than the neutrino ones, and that however many proton models are viable. The basic parameters of such models are relatively large γg and not very large zmax . The allowance for He4 admixture also relaxes the restrictions. However we foresee that future CTA measurements of γ-ray spectrum at Eγ≃(600−800) GeV, as well as resolving of more individual γ-ray sources, may rule out the proton-dominated cosmic ray models.
We examine the hypothesis of decaying heavy dark matter (HDM) in the context of the IceCube highest energy neutrino events and recent limits on the diffuse flux of high-energy photons. We consider ...dark matter (DM) particles X of mass 106?MX?1016 GeV decaying on tree level into X???¯, X?e+e?, and X?qq¯. The full simulation of hadronic and electroweak decay cascades and the subsequent propagation of the decay products through the interstellar medium allows us to determine the permitted values of MX. We show that for leptonic decay channels it is possible to explain the IceCube highest energy neutrino signal without overproducing high-energy photons for MX?5.5×107 GeV and 1.5×108?MX?1.5×109 GeV, while hadronic decays contradict the gamma-ray limits for almost the whole range of MX values considered. The leptonic hypothesis can be probed by operating and planned gamma-ray observatories: For instance, the currently upgrading Carpet experiment will be capable to test a significant part of the remaining parameter window within one year of observation.
We aim to explain in a unified way the experimental data on ultrahigh-energy cosmic rays (UHECRs) and neutrinos, using a single source class and obeying limits on the extragalactic diffuse gamma-ray ...background. If UHECRs only interact hadronically with gas around their sources, the resulting diffuse cosmic-ray (CR) flux can be matched well to the observed one, providing at the same time large neutrino fluxes. Since the required fraction of heavy nuclei is, however, rather large, the maxima of air showers in the Earth’s atmosphere induced by UHECRs with energies E≳3×1018 eV would be too high. Therefore, additional photohadronic interactions of UHECRs close to the accelerator have to be present, in order to modify the nuclear composition of CRs in a relatively narrow energy interval. We thus include both photon and gas backgrounds and combine the resulting CR spectra with the high-energy part of the Galactic CR fluxes predicted by the escape model. As result, we find a good description of experimental data on the total CR flux, the mean shower maximum depth Xmax and its width rms(Xmax) in the whole energy range above E≃1017 eV. The predicted high-energy neutrino flux matches IceCube measurements, while the contribution to the extragalactic diffuse gamma ray background is of order 30%.
We present constraints on the lifetime of the superheavy decaying dark matter branching to the qq̅ channel in the mass range 1019–1025 eV based on the directional limits on the ultra-high-energy ...(UHE) gamma rays from dwarf spheroidal galaxies (dSphs) and the Milky Way (MW) centre obtained by the Pierre Auger Observatory and the Telescope Array experiment. Attenuation effects during the propagation of UHE photons towards Earth are taken into account. The strongest constraints are derived for the MW centre and have an order of 1020 yr. We conclude that the UHE diffuse gamma-ray limits provide more efficient signature for the superheavy DM search than the directional gamma-ray limits.
Recently, the IceCube collaboration reported first evidence for the astrophysical neutrinos. Observation corresponds to the total astrophysical neutrino flux of the order of 3 × 10
−8
GeV cm
−2
s
−1
...sr
−1
in a PeV energy range 1. Active galactic nuclei (AGN) are natural candidate sources for such neutrinos. To model the neutrino creation in AGNs, we study photopion production processes on the radiation field of the Shakura-Sunyaev accretion discs in the black hole vicinity. We show that this model can explain the detected neutrino flux and at the same time avoids the existing constraints from the gamma-ray and cosmic-ray observations.
Abstract
Baikal-GVD is a gigaton-scale underwater neutrino telescope currently under construction in Lake Baikal. Its principal components are optical modules, registering photons propagating through ...the telescope’s working volume. Part of the activations of the optical modules are due to the natural luminescence of the water, and thus appear as noise in the data. We present a neural network, which efficiently rejects this background and reaches 97% signal purity (precision) and 99% survival efficiency (recall) on the Monte-Carlo data. The neural network has a U-net like architecture based on the temporal structure of optical modules activations.
The Telescope Array (TA) observatory utilizes fluorescence detectors and surface detectors (SDs) to observe air showers produced by ultra high energy cosmic rays in Earth's atmosphere. Cosmic-ray ...events observed in this way are termed hybrid data. The depth of air shower maximum is related to the mass of the primary particle that generates the shower. This paper reports on shower maxima data collected over 8.5 yr using the Black Rock Mesa and Long Ridge fluorescence detectors in conjunction with the array of SDs. We compare the means and standard deviations of the observed X max distributions with Monte Carlo X max distributions of unmixed protons, helium, nitrogen, and iron, all generated using the QGSJet II-04 hadronic model. We also perform an unbinned maximum likelihood test of the observed data, which is subjected to variable systematic shifting of the data X max distributions to allow us to test the full distributions, and compare them to the Monte Carlo to see which elements are not compatible with the observed data. For all energy bins, QGSJet II-04 protons are found to be compatible with TA hybrid data at the 95% confidence level after some systematic X max shifting of the data. Three other QGSJet II-04 elements are found to be compatible using the same test procedure in an energy range limited to the highest energies where data statistics are sparse.
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