Related papers: UHECR besides CenA: hints of galactic sources
Ultra High Energy Cosmic Rays (UHECR) can be a signal from very early (post-inflationary) Universe. At this cosmological epoch Topological Defects (TD) and long-lived suprheavy (SH) particles are expected to be naturally and effectively…
Low-luminosity gamma-ray bursts (GRBs) with luminosity . 10^49erg/s probably consititute a distinct population from the classic high-luminosity GRBs. They are the most luminous objects detected so far within ~ 100 Mpc, the horizon distance…
The origin of ultra-high energy cosmic rays (UHECRs) is still unknown. It has recently been proposed that UHECR anisotropies can be attributed to starburst galaxies or active galactic nuclei. We suggest that the latter is more likely and…
Ultra-high energy cosmic rays (UHECRs) may originate from the decay of massive relic particles in the dark halo of the Galaxy, or they may be produced by supermassive black holes in the nuclei of nearby galaxies. The anisotropy in the…
The motivation and the current status of top-down models as sources of ultrahigh energy cosmic rays (UHECR) are reviewed. Stimulated by the AGASA excess, they were proposed as the main source of UHECRs beyond the GZK cutoff. Meanwhile…
The conjecture that ultra high energy cosmic rays (UHECRs) are actually strangelets is discussed. Besides the reason that strangelets can do as cosmic rays beyond the GZK-cutoff, another argument to support the conjecture is addressed in…
The cosmic ray spectrum has been shown to extend well beyond 10^{20}eV. With nearly 20 events observed in the last 40 years, it is now established that particles are accelerated or produced in the universe with energies near 10^{21}eV. In…
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…
GeV-TeV gamma-rays and PeV-EeV neutrino backgrounds provide a unique window on the nature of the ultra-high-energy cosmic-rays (UHECRs). We discuss the implications of the recent Fermi-LAT data regarding the extragalactic gamma-ray…
Ultra High Energy Cosmic Rays are the most energetic particles directly measured, reaching orders of magnitude above those attained in the LHC. The Pierre Auger Observatory is shedding light onto the long-standing mysteries of their nature…
In this paper, the production of neutrinos and photons by ultra high energy cosmic rays (UHECR) interacting with the extragalactic background radiation is studied. Centaurus A is assumed as the prime source of UHECR and the possibility to…
Ultra-high-energy cosmic rays (UHECR) scattering off the cosmic relic neutrino background have recently gained renewed interest in the literature. Current data suggest that (UHECR) are predominantly made of heavy nuclei. Similar to the…
As recently suggested, nearby quasar remnants are plausible sites of black-hole based compact dynamos that could be capable of accelerating ultra-high energy cosmic rays (UHECRs). In such a model, UHECRs would originate at the nuclei of…
We study possible correlations between ultrahigh energy cosmic rays (UHECRs), observed by Auger, AGASA and Yakutsk, and nearby active galactic nuclei (AGNs) and $Fermi$ sources. We consider the deflection effects by a Galactic magnetic…
The Fermi Large Area Telescope (Fermi LAT) collaboration has recently reported on 50 months of measurements of the isotropic Extragalactic Gamma Ray Background (EGRB) spectrum between $100\mbox{MeV}$ and $820\mbox{GeV}$. Ultrahigh Energy…
Over the last decade, observations have shown that the mean mass of ultra-high-energy cosmic rays (UHECRs) increases progressively toward the highest energies. However, the precise composition is still unknown, and several theoretical…
We investigate whether ultra--high energy cosmic rays (UHECR) may be preferentially produced in massive galaxy clusters, by looking for correlations between UHECR directions and those of x-ray clusters. We find an excess-above-random of…
Ultrahigh-energy cosmic rays (UHECRs) arrive at Earth from the most energetic astrophysical accelerators in the universe. They collide with atoms in the upper atmosphere with energies about ten times higher than any man-made accelerator,…
We calculate the number density and luminosity of the sources of ultra high energy cosmic rays (UHECRs), using the information about the small scale anisotropies and the observed spectra. We find that the number of doublets and triplets…
Ultra-high energy cosmic rays (UHECRs) beyond the Greisen-Zatsepin-Kuzmin (GZK) cut-off provide us with a unique opportunity to understand the universe at extreme energies. Secondary GZK photons and GZK neutrinos associated with the same…