Astrophysical neutrinos are expected to be produced in the interactions of ultra-high energy cosmic-rays with surrounding photons. The fluxes of the astrophysical neutrinos are highly dependent on the characteristics of the cosmic-ray sources, such as their cosmological distributions. We study possible constraints on the properties of cosmic-ray sources in a model-independent way using experimentally obtained diffuse neutrino flux above 100 PeV. The semi-analytic formula is derived to estimate the cosmogenic neutrino fluxes as functions of source evolution parameter and source extension in redshift. The obtained formula converts the upper-limits on the neutrino fluxes into the constraints on the cosmic-ray sources. It is found that the recently obtained upper-limit on the cosmogenic neutrinos by IceCube constrains the scenarios with strongly evolving ultra-high energy cosmic-ray sources, and the future limits from an 1 km^3 scale detector are able to further constrain the ultra-high energy cosmic-rays sources with evolutions comparable to the cosmic star formation rate.
We demonstrate that young star clusters have a $γ$-ray surface brightness comparable to that of the diffuse Galactic emission (DGE), and estimate that their sky coverage in the direction of the inner Galaxy exceeds unity. We therefore suggest that they comprise a significant fraction of the DGE.
Cosmic rays (CRs) generate diffuse emission while interacting with the Galactic magnetic field (B-field), the interstellar gas and the radiation field. This diffuse emission extends from radio, microwaves, through X-rays, to high-energy gamma rays. Diffuse emission has considerably increased the interest of the astrophysical community due to recent detailed observations by Planck, Fermi-LAT, and by very-high-energy Cherenkov telescopes. Observations of this emission and comparison with detailed predictions are used to gain information on the properties of CRs, such as their density, spectra, d…
Very recently, the Tibet-AS$γ$ collaboration reported the detection of $γ$ rays from the galactic disk in the energy range of 100 TeV -- 1 PeV. Remarkably, many of these $γ$ rays were observed apart from known very high energy (E$>$ 100 GeV) $γ$-ray sources. These results are best understood if these diffuse $γ$ rays: 1) were produced by a conventional rather than an exotic (i.e. dark matter decay or annihilation) process, 2) have a hadronic rather than a leptonic origin, 3) were produced in impulsive rather than stable sources or, alternatively, in optically thick sources. In addition to that…
We show that the observed fluxes, spectra and sky distributions of the high energy diffuse backgrounds of astronomical neutrinos, gamma rays and cosmic ray positrons satisfy simple relations expected from their common production in hadronic collisions of high energy cosmic rays (CRs) with diffuse matter. This provides compelling evidence that the high energy neutrino, gamma ray, and positron backgrounds have a common origin - hadronic meson production by cosmic rays in our Galaxy and in external galaxies rather than through the decay/annihilation of dark matter particles.
Using diffuse radio emission in clusters of galaxies to probe the cosmic web, cosmic rays and dark matter
漫射射电源的研究对于我们了解星系团的物理条件以及大尺度磁场在相对论粒子在团内介质（ICM）中传播中所起的作用是必不可少的。由于耗散过程，ICM的热等离子体包含无用的信息的结构和CR的形成。这种过去和现在的信息是由它的非热辐射完整地携带的，这种非热辐射是由高度相对论性的粒子在大尺度磁场中螺旋运动引起的。漫射射电辐射与活动星系核现象无关，也没有光学对应物。相反，它与ICM相关，其特征在于陡峭的频谱。低表面射电亮度特征被认为是通过相对论电子的残余群体的再加速或与ICM的质子-质子碰撞形成的。漫射射电源通常分为“遗迹”、“晕”、“迷你晕”和“射电幽灵”。我们用67个红移为0.02 < z < 0.1的邻近星系团的样本来研究漫射射电辐射与大尺度结构（宇宙网）、暗物质（DM）和宇宙射线（CR）之间的关系。我们的样本的集群在低红移包含地区的无线电流量低于Jy水平是非常适合的DM的研究。DM晕可以显著地有助于在低亮度下的源的计数。我们报告正在进行的工作。
The Milky Way is surrounded by a gravitationally bound gas corona extending up to the Galaxy's virial radius. Interactions of cosmic-ray particles with this gas give rise to energetic secondary gamma rays and neutrinos. We present a quantitative analysis of the neutrino and gamma-ray fluxes from the corona of the Milky Way together with a combined contribution of coronae of other galaxies. The high-energy neutrino flux is insufficient to explain the IceCube results, while the contribution to the FERMI-LAT diffuse gamma-ray flux is not negligible.
Cosmic rays accelerated to ultra-high energies (E>4x10^19 eV) in electric fields in accretion discs around supermassive black holes are discussed. Particle injection spectra are assumed to be harder than those formed in acceleration on shock fronts. It turned out that cosmic rays with injection spectra supposed contribute a little in the particle flux detected with ground-based arrays. But in the extragalactic space particle generate a noticeable flux of the diffuse gamma-ray emission compared with the data obtained with the Fermi LAT instrument (onboard the Fermi space observatory). The inten…
We derive the maximum fraction of energy emitted in the form of massive (Kaluza- Klein) gravitons by core collapse supernovae, and the corresponding minimal extra-dimensional Planck mass M* in the ADD gravity framework at TeV scales. Our constraints arise: a) from the extragalactic gamma ray background observed by Fermi-LAT after astrophysical sources have been removed, and b) via the residual galactic emission left after astrophysical and potentially dark matter emission have been removed. We focus on a number of extra dimensions 3 and 4, since M* is then in the TeV range, where astrophysical…
The Tibet ASgamma experiment just reported their measurement of sub-PeV diffuse gamma ray emission from the Galactic disk, with the highest energy up to 957 TeV. These gamma-rays are most likely the hadronic origin by cosmic ray interaction with interstellar gas in the Galaxy. This measurement provides direct evidence to the hypothesis that the Galactic cosmic rays can be accelerated beyond PeV energies. In this work, we try to explain the sub-PeV diffuse gamma-ray spectrum within cosmic rays diffusive propagation model. We find there is a tension between the sub-PeV diffuse gamma rays and the…
The extragalactic sources of ultra-high-energy (E > 4x10^19 eV) cosmic rays that make a small contribution to the flux of particles recorded by ground-based arrays are discussed. We show that cosmic rays from such sources can produce a noticeable diffuse gamma-ray flux in intergalactic space compared to the the data obtained with Fermi LAT (onboard the Fermi space observatory). A possible type of active galactic nuclei (AGNs) in which cosmic-ray protons can be accelerated to energies 1021 eV is considered as an illustration of such sources. We conclude that ultra-high-energy cosmic rays from t…
Recent direct measurements of Galactic cosmic ray spectra by balloon/space-borne detectors reveal spectral hardenings of all major nucleus species at rigidities of a few hundred GV. The all-sky diffuse gamma-ray emissions measured by the Fermi Large Area Telescope also show spatial variations of the intensities and spectral indices of cosmic rays. These new observations challenge the traditional simple acceleration and/or propagation scenario of Galactic cosmic rays. In this work we propose a spatially-dependent diffusion scenario to explain all these phenomena. The diffusion coefficient is as…
The propagation of particles accelerated at supernova remnant shocks and escaping the parent remnants is likely to proceed in a strongly non-linear regime, due to the efficient self-generation of Alfvén waves excited through streaming instability near the sources. Depending on the amount of neutral hydrogen present in the regions around the sites of supernova explosions, cosmic rays may accumulate an appreciable grammage in the same regions and get self-confined for non-negligible times, which in turn results in an enhanced rate of production of secondaries. Here we calculate the contribution …
The diffuse $γ$-ray emission was measured up to $957$ TeV by the Tibet-AS$γ$ experiment recently. Assuming that it is produced by the hadronic interaction between cosmic ray nuclei and the interstellar medium, it requires that the cosmic ray nuclei should be accelerated well beyond PeV energies. Measurements of the cosmic ray spectra for different species show diverse results at present. The Tibet experiments showed that the spectrum of proton plus helium has an early knee below PeV. If this is correct, the diffuse $γ$-ray emission would suggest an additional component of Galactic cosmic rays …
Recent high-energy data from Fermi-LAT on the diffuse gamma-ray background have been used to set among the best constraints on annihilating TeV cold dark matter candidates. In order to assess the robustness of these limits, we revisit and update the calculation of the isotropic extragalactic gamma-ray intensity from dark matter annihilation. The emission from halos with masses $\geq10^{10}\,M_{\odot}$ provides a robust lower bound on the predicted intensity. The intensity including smaller halos whose properties are extrapolated from their higher mass counterparts is typically 5 times higher, …
We demonstrate that the UHECRs produced in the nuclear cascade in the jet of Low-Luminosity Gamma-Ray Bursts (LL-GRBs) can describe the UHECR spectrum and composition and, at the same time, the diffuse neutrino flux at the highest energies. The radiation density in the source simultaneously controls the neutrino production and the development of the nuclear cascade, leading to a flux of nucleons and light nuclei describing even the cosmic-ray ankle at $5 \times 10^{18}$ eV. The derived source parameters are consistent with population studies, indicating a baryonic loading factor of about ten. …
We calculate the fluxes of neutrinos and gamma rays from interactions of cosmic rays with interstellar matter in our galaxy. We use EPOS-LHC, SIBYLL and GHEISHA to obtain the yield of these particles in proton, helium and iron collisions at kinetic energies between 1 and 10^8 GeV, and we correlate the cosmic ray density with the mean magnetic field strength in the disk and the halo of our galaxy. We find that at E>1 PeV the fluxes depend very strongly on the cosmic-ray composition, whereas at 1-5 GeV the main source of uncertainty is the cosmic-ray spectrum out of the heliosphere. We show that…
A flux of cosmic rays (CRs) propagating through a diffuse ionized gas can excite MHD waves, thus generating magnetic disturbances. We propose a generic model of CR penetration into molecular clouds through their diffuse envelopes, and identify the leading physical processes controlling their transport on the way from a highly ionized interstellar medium to a dense interior of the cloud. The model allows us to describe a transition between a free streaming of CRs and their diffusive propagation, determined by the scattering on the self-generated disturbances. A self consistent set of equations,…
Can diffuse X-rays be important in driving photoionisation in molecular clouds?
Max Planck Institute for Extraterrestrial Physics（马克斯·普朗克地外物理研究所）；Physics Department, Technion - Israel Institute of Technology（以色列理工学院物理系）；Faculty of Physics, University of Duisburg-Essen（杜伊斯堡-埃森大学物理学院）；INAF–Osservatorio Astrofisico di Arcetri（意大利国家天体物理研究所阿切特里天文台）
We report, for the first time, the long-awaited detection of diffuse gamma rays with energies between 100 TeV and 1 PeV in the Galactic disk. Particularly, all gamma rays above 398 TeV are observed apart from known TeV gamma-ray sources and compatible with expectations from the hadronic emission scenario in which gamma rays originate from the decay of $π^0$'s produced through the interaction of protons with the interstellar medium in the Galaxy. This is strong evidence that cosmic rays are accelerated beyond PeV energies in our Galaxy and spread over the Galactic disk.
The Picard code for the numerical solution of the Galactic cosmic ray propagation problem allows for high-resolution models that acknowledge the 3D structure of our Galaxy. Picard was used to determine diffuse gamma-ray emission of the Galaxy over the energy range from 100 MeV to 100 TeV. We discuss the impact of a cosmic-ray source distribution aligned with the Galactic spiral arms for a range of such spiral-arm models. As expected, the impact on the gamma-ray emission is most distinct in the inverse-Compton channel, where imprints of the spiral arms are visible and yield predictions that are…
Cosmic ray accelerators like supernova and hypernova remnants in star forming galaxies are one of the most plausible sources of the IceCube observed diffuse astrophysical neutrinos. The neutrino producing hadronic processes will also produce a diffuse gamma ray flux, constrained by the Fermi-LAT bounds. The fact that point sources like blazars also contribute to the diffuse gamma ray flux implies large gamma opacity of the neutrino sources. Indeed, for these high redshift star forming galaxies the gamma absorption during the intergalactic propagation can be significant. In addition, large gamm…
