Motivated by recent Pierre Auger result on the correlation of the highest-energy cosmic rays with the nearby active galactic nuclei, we explore possible ultrahigh energy cosmic ray (UHECR) source distributions and their effects on GZK horizons. Effects on GZK horizons by local over-density of UHECR sources are examined carefully with constraints on the degree of local over-density inferred from the measured UHECR spectrum. We include the energy calibration effect on the Pierre Auger data in our studies. We propose possible local over-densities of UHECR sources which are testable in the future cosmic ray astronomy.
Motivated by recent Pierre Auger result on the correlation of the highest-energy cosmic rays with the nearby active galactic nuclei, we explore possible ultrahigh energy cosmic ray (UHECR) source distributions and their effects on GZK horizons. Effects on GZK horizons by local over-density of UHECR sources are examined carefully with constraints on the degree of local over-density inferred from the measured UHECR spectrum. We include the energy calibration effect on the Pierre Auger data in our studies. We propose possible local over-densities of UHECR sources which are testable in the future …
The apparent lack of suitable astrophysical sources for the observed highest energy cosmic rays (UHECRs) within $\approx 20$ Mpc is the "GZK Paradox". We constrain representative models of the extra-galactic magnetic field structure by Faraday Rotation measurements; limits are at the $μ$G level rather than the nG level usually assumed. In such fields, even the highest energy cosmic rays experience large deflections. This allows nearby AGNs (possibly quiet today) or GRBs to be the source of ultra-high energy cosmic rays without contradicting the GZK distance limit.
Scattering processes in the cosmic microwave background limit the propagation of ultra high energy charged particles in our Universe. For extragalactic proton sources resonant photopion production results in the famous Greisen-Zatsepin-Kuzmin (GZK) cutoff at about 4x10^10 GeV expected in the spectrum observed on Earth. The faint flux of ultra high energy cosmic rays of less than one event per year and cubic kilometer and the large systematic uncertainties in the energy calibration of cosmic ray showers is a challenge for cosmic ray observatories and so far the GZK cutoff has not been unambiguo…
The Ultra High Energy (UHE) neutrino scattering onto relic cosmic neutrinos in galactic and local halos offers an unique way to overcome GZK cut-off. The UHE nu secondary of UHE photo-pion decays may escape the GZK cut-off and travel on cosmic distances hitting local light relic neutrinos clustered in dark halos. The Z resonant production and the competitive W^+W^-, ZZ pair production define a characteristic imprint on hadronic consequent UHECR spectra. This imprint keeps memory both of the primary UHE nu spectra as well as of the possible relic neutrino masses values, energy spectra and relic…
The nature of the unknown sources of ultra-high energy cosmic rays can be revealed through the detection of the GZK feature in the cosmic ray spectrum, resulting from the production of pions by ultra-high energy protons scattering off the cosmic microwave background. Here we show that the GZK feature cannot be accurately determined with the small sample of events with energies $\sim 10^{20}$ eV detected thus far by the largest two experiments, AGASA and HiRes. With the help of numerical simulations for the propagation of cosmic rays, we find the error bars around the GZK feature are dominated …
We analyze the existing evidence that BL Lacertae objects (BL Lacs) are sources of the highest-energy cosmic rays. We argue that three independent signatures observed in the real data -- (1) improvement of correlations with corrections of trajectories for the Galactic magnetic field; (2) connection between gamma-ray and UHECR emissions; (3) non-uniform distribution of correlating rays over the sky -- are consistent with the hypothesis that a substantial fraction of cosmic rays in the energy range 40-60 EeV are protons accelerated in BL Lacs.
We calculate numerically the spectrum of ultra-high energy cosmic rays on Earth assuming that their sources are distributed in space like the observed galaxies. We use the CfA2 and the PSCz galaxy redshift surveys to model the local galaxy distribution, properly taking into account the galaxy selection functions for each survey. When the survey selection effects are included, we find that the local overdensity is only a factor of two, an order of magnitude less than used in some earlier studies. An overdensity of two is not enough to bridge the gap between the predicted number of events above …
The expected Ultra High Energy Neutrino signals from PeVs up to GZK energies may arise as Upward and Horizontal Tau air Showers, UPTAUS and HORTAUS, flashing toward mountain peaks, airplanes, balloons and satellites. The Areas, Volumes and Masses from these Terrestrial Corona at each height are estimated for present and future Tau Air-Showering experiments. While observing from high mountains these masses are comparable to few km^3 volumes above EeVs neutrino energies and they may even exceed 150 km^3 at GZK energies, (E > = 10^19 eV), while being recording from a satellite looking toward terr…
The status of the field of ultrahigh energy cosmic rays is summarized, from the point of view of the latest results of the High Resolution Fly's Eye (HiRes) Experiment. HiRes results are presented, and compared with those of the Akeno Giant Air Shower Array (AGASA), plus the Telescope Array and Pierre Auger experiments. The HiRes measurements of the cosmic ray spectrum, and the observation of the GZK cutoff are presented. HiRes results on composition, searches for anisotropy, measurement of the proton-air total cross section, and shapes of shower profiles are presented.
Cosmic rays of energy higher than 10^19 eV may be explained by topological defects produced in the early stages of universe. Two suitable alternatives are: necklaces formed by magnetic monopoles connected by strings, and vortons which are loops stabilized by superconducting currents. The former are uniformly distributed in the universe, may account for cosmic rays above the ankle, suffer a transient GZK cutoff with a subsequent recovery and isotropy of observations is expected. The latter are concentrated in the galactic halo, require an additional extragalactic contribution between the ankle …
The HiRes and AGASA Collaborations have published contradictory energy spectra for energies above the GZK cut-off. In this article, we investigate the acceptance of fluorescence telescopes to different primary particles at the highest energies. Using CORSIKA shower simulations without and with the new pre-showering scheme, which allows photons to interact in the Earth magnetic field, we estimate the aperture of the HiRes I telescope for gammas and protons primaries. We calculate the dependence of the telescope sensitivity to primary particle identity. We also investigate the possibility that s…
EUSO experiment, while monitoring the downward Earth atmosphere layers, may observe among common Ultra High Energy Cosmic Rays, UHECR, also High Energy Neutrino-Induced Showers either blazing upward to the detectors at high (PeVs) energies or at much higher GZK E >= 10^19 eV energies, showering horizontally in air or vertically downward. A small fraction of these upward, horizontal and vertical Shower maybe originated by direct astrophysical UHE neutrino interacting on terrestrial air layers itself; however the dominant UHE neutrino signal are Upward and Horizontal Tau Air-Showers, UPTAUS and …
Ultra High Energy (UHE) neutrino Astronomy and relic Neutrino masses may play a key role in solving the Ultra High Energy Cosmic Ray (UHECR) puzzle within the Z-Showering model. Tau air-shower originated by UHE neutrino in matter may probe and amplify this expected UHE neutrino Astronomy. The discover of upcoming and horizontal tau air-showers (UPTAUs, HORTAUs), born by UHE, nu_tau interacting inside mount chains or along Earth Crust crown masses at the Horizons edges, will greatly amplify the single UHE nu_tau track. Observing UPTAUs and HORTAUs along their line of showering, from higher ball…
The discoveries of the GZK cutoff with the HiRes and Auger Observatories and the discovery by Auger of clustering of >~60 EeV ultra-high energy cosmic rays (UHECRs) towards nearby <~75 Mpc) AGNs along the supergalactic plane establishes the astrophysical origin of the UHECRs. The likely sources of the UHECRs are gamma-ray bursts and radio-loud AGNs because: (1) they are extragalactic; (2) they are sufficiently powerful; (3) acceleration to ultra-high energies can be achieved in their relativistic ejecta; (4) anomalous X-ray and gamma-ray features can be explained by nonthermal hadron accelerat…
UHE neutrinos may transfer highest cosmic-rays energies overcoming $2.75K^\circ$ BBR and radio-waves opacities (the GZK cut off) from most distant AGN sources at the age of the Universe. These UHE $ν$ might scatter onto those (light and cosmological) relic neutrinos clustered around our galactic halo or nearby neutrino hot dark halo clustered around the AGN blazar and its jets. The branched chain reactions from a primordial nucleon (via photo production of pions and decay to UHE neutrinos) toward the consequent beam dump scattering on galactic relic neutrinos is at least three order of magnitu…
The main results from the Auger Observatory are described. A steepening of the spectrum is observed at the highest energies, supporting the expectation that above $4\times 10^{19}$ eV the cosmic ray energies are significantly degraded by interactions with the CMB photons (the GZK effect). This is further supported by the correlations observed above $6\times 10^{19}$ eV with the distribution of nearby active galaxies, which also show the potential of Auger to start the era of charged particle astronomy. The lack of observation of photons or neutrinos strongly disfavors top-down models, and thes…
Along the years HiRes and AGASA experiments have explored the fluorescence and the ground array experimental techniques to measure extensive air showers, being both essential to investigate the ultra-high energy cosmic rays. However, such Collaborations have published contradictory energy spectra for energies above the GZK cut-off. In this article, we investigate the acceptance of fluorescence telescopes to different primary particles at the highest energies. Using CORSIKA and CONEX shower simulations without and with the new pre-showering scheme, which allows photons to interact in the Earth …
In this paper we briefly discuss the problem of the origin of Ultra High Energy Cosmic Rays in the framework of Top-Down models. We show that, for high energy of decays and in a wide range of spectra of injected protons, their extragalactic flux is consistent with the observed fluxes of cosmic rays in the energy range 0.1 E_{GZK}< E < 10E_{GZK}. For suitable energy and spectra of injected protons, the contribution of galactic sources is moderate, in this energy range, but it dominates at smaller and larger energies. In such models we can expect that at these energies the anisotropy of cosmic r…
A new method to derive an upper limit on photon primaries from small data sets of air showers is developed which accounts for shower properties varying with the primary energy and arrival direction. Applying this method to the highest-energy showers recorded by the AGASA experiment, an upper limit on the photon fraction of 51% (67%) at a confidence level of 90% (95%) for primary energies above 1.25 * 10^20 eV is set. This new limit on the photon fraction above the GZK cutoff energy constrains the Z-burst model of the origin of highest-energy cosmic rays.
The observation of cosmic--ray events above the Greisen-Kuzmin-Zatsepin (GZK) cutoff of $\sim 5\times 10^{19}$ eV challenges orthodox modeling. We discuss a possible solution which uses standard hot Big Bang cosmology and Standard Model (SM) particle physics augmented only by $\lsim $ eV neutrino masses as suggested by solar, atmospheric, and terrestrial neutrino detection. In this scheme, cosmic ray neutrinos from distant, highest-energy sources annihilate resonantly on the relic-neutrino background to produce Z-bosons. The highly-boosted ($γ_Z\sim 10^{11}$) Z's instantly decay, producing "Z-…
We study the small scale anisotropy signal expected at the Pierre Auger Observatory in the next 1, 5, 10, and 15 years of operation, from sources of ultra-high energy (UHE) protons. We numerically propagate UHE protons over cosmological distances using an injection spectrum and normalization that fits current data up to $\sim 10^{20}\eV$. We characterize possible sources of ultra-high energy cosmic rays (UHECRs) by their mean density in the local Universe, $\barρ = 10^{-r}$ Mpc$^{-3}$, with $r$ between 3 and 6. These densities span a wide range of extragalactic sites for UHECR sources, from co…
We examine the anisotropy of the arrival directions of twenty seven ultra high energy cosmic rays detected by the Pierre Auger Collaboration. We confirm the anisotropy of the arrival directions of these events and find a significant correlation with the updated definition of the supergalactic plane at distances up to 70 Mpc, A Monte Carlo calculation of isotropic source distribution suggests a chance probability for isotropic event arrival direction distribution of 2-6$\times10^{-4}$.
Measurements of the arrival directions of cosmic rays have not revealed their sources. High energy neutrino telescopes attempt to resolve the problem by detecting neutrinos whose directions are not scrambled by magnetic fields. The key issue is whether the neutrino flux produced in cosmic ray accelerators is detectable. It is believed that the answer is affirmative, both for the galactic and extragalactic sources, provided the detector has kilometer-scale dimensions. We revisit the case for kilometer-scale neutrino detectors in a model-independent way by focussing on the energetics of the sour…
Resonant photopion production with the cosmic microwave background predicts a suppression of extragalactic protons above the famous Greisen-Zatsepin-Kuzmin cutoff at about E_{GZK} ~ 5 x 10^10 GeV. Current cosmic ray data measured by the AGASA and HiRes Collaborations do not unambiguously confirm the GZK cutoff and leave a window for speculations about the origin and chemical composition of the highest energy cosmic rays. In this work we analyze the possibility of strongly interacting neutrino primaries and derive model-independent quantitative requirements on the neutrino-nucleon inelastic cro…
The absence of the expected GZK cutoff strongly challenges the notion that the highest-energy cosmic rays are of distant extragalactic origin. We discuss the possibility that these ultra-high-energy events originate in our Galaxy and propose that they may be due to iron nuclei accelerated from young, strongly magnetic neutron stars. Newly formed pulsars accelerate ions from their surface through relativistic MHD winds. We find that pulsars whose initial spin periods are shorter than $\sim 4 (B_S/10^{13}{\rm G})$ ms, where $B_S$ is the surface magnetic field, can accelerate iron ions to greater…
The significant attenuation of the cosmic-ray flux above $\sim 5 10^{19}$ eV suggests that the observed high-energy spectrum is shaped by the so-called GZK effect. This interaction of ultra-high-energy cosmic rays (UHECRs) with the ambient radiation fields also affects their composition. We review the effect of photo-dissociation interactions on different nuclear species and analyze the phenomenology of secondary proton production as a function of energy. We show that, by itself, the UHECR spectrum does not constrain the cosmic-ray composition at their extragalactic sources. While the propagat…
The hypothesis that the electron neutrino is a tachyon with |m|=sqrt(-m^2) = 0.5 eV/c^2 is consistent with certain properties of the cosmic ray spectrum, including: the existence of a change in power law (the "knee") at E = 10^15 eV, the E^-3 power law after the knee, another change in power law (the "ankle") at E = 10^19 eV, the changes in composition above the knee, the change in anisotropy at the knee, and the absence of a GZK cutoff above E = 4 x 10^19 eV. The hypothesis predicts a substantial flux of cosmic ray neutrons in a narrow energy region just above the knee of the spectrum.
The GZK cutoff predicted at the Ultra High Energy Cosmic Ray (UHECR) spectrum as been observed by the HiRes and Auger experiments. The results put severe constraints on the effect of Lorentz Invariance Violation(LIV) which has been introduced to explain the absence of GZK cutoff indicated in the AGASA data. Assuming homogeneous source distribution with a single power law spectrum, we calculate the spectrum of UHECRs observed on Earth by taking the processes of photopion production, $e^+e^-$ pair production and adiabatic energy loss into account. The effect of LIV is also taken into account in …
We present results of numerical simulations of the propagation of ultra high energy cosmic rays (UHECRs) over cosmological distances, aimed at quantifying the statistical significance of the highest energy data on the spectrum and small scale anisotropies as detected by the AGASA experiment. We assess the significance of the lack of a GZK feature and its compatibility with the reported small scale anisotropies. Assuming that UHECRs are protons from extragalactic sources, we find that the small scale anisotropies are incompatible with the reported spectrum at a probability level of $2 \times 10…
We conduct a review of experimental results on Ultra-High Energy Cosmic Rays (UHECR's) including measurements of the features of the spectrum, the composition of the primary particle flux and the search for anisotropy in event arrival direction. We find that while there is a general consensus on the features in the spectrum -- the Second Knee, the Ankle, and (to a lesser extent) the GZK Cutoff -- there is little consensus on the composition of the primaries that accompany these features. This lack of consensus on the composition makes interpretation of the agreed upon features problematic. The…
We report on the solar diurnal variation of the galactic cosmic-ray intensity observed by the Tibet III air shower array during the period from 1999 to 2003. In the higher-energy event samples (12 TeV and 6.2 TeV), the variations are fairly consistent with the Compton-Getting anisotropy due to the terrestrial orbital motion around the sun, while the variation in the lower-energy event sample (4.0 TeV) is inconsistent with this anisotropy. This suggests an additional anisotropy superposed at the multi-TeV energies, e.g. the solar modulation effect. This is the highest-precision measurement of t…
The recent discovery by the Pierre Auger collaboration of anisotropy in the arrival directions of the highest energy cosmic rays, correlated with the positions of nearby active galactic nuclei, encourages the search for counterpart TeV gamma-ray emission. Approximately half of the sky viewed by the southern hemisphere Pierre Auger experiment is also visible at reasonable elevations for the northern hemisphere gamma-ray telescope array, VERITAS. We report on first observations by VERITAS of regions associated with the arrival directions of ultra-high energy cosmic ray events.
It is difficult for conventional sources to accelerate cosmic ray particles to the highest energies that have been observed. Topological defects such as monopoles and strings overcome this difficulty, because their natural energy scale is at or above the observed energies. Monopoles connected by strings are a particularly attractive source, because they would cluster in the galactic halo and thus explain the absence of the GZK cutoff. Heavy monopoles connected by light strings could last for the age of the universe as required. Further observations might support this model by detection of the …
Data collected by the Pierre Auger Observatory provide evidence for anisotropy in the arrival directions of the cosmic rays with the highest energies, which are correlated with the positions of relatively nearby active galactic nuclei (AGN) \cite{science}. The correlation has maximum significance for cosmic rays with energy greater than ~ 6x10^{19}$ eV and AGN at a distance less than ~ 75 Mpc. We have confirmed the anisotropy at a confidence level of more than 99% through a test with parameters specified {\em a priori}, using an independent data set. The observed correlation is compatible with…
The observation of cosmic ray particles with unexpected high energies is pushing astroparticle physics into a period of rapid progress both theoretically and experimentally. Different proposed models for the generation of these particles are constrained by the absence of the predicted GZK cutoff in the cosmic ray spectrum and by the composition and the distribution of arrival directions observed. The database increase due to the Pierre Auger Observatory will provide a clearer picture of the spectral anisotropy and properties of such high energy particles, enabling tests of their origin and nat…
The universe should be dark at energies exceeding $\sim 5\times 10^{19}$ eV. This simple but solid prediction of our best known particle physics is not confirmed by observations, that seem to suggest a quite different picture. Numerous events have in fact been detected in this energy region, with spectra and anisotropy features that defy many conventional and unconventional explanations. Is there a problem with known physics or is this a result of astrophysical uncertainties? Here we try to answer these questions, in the light of present observations, while discussing which information future …
A natural interpretation of the correlation between nearby Active Galactic Nuclei (AGN) and the highest-energy cosmic rays observed recently by the Pierre Auger Collaboration is that the sources of the cosmic rays are either AGN or other objects with a similar spatial distribution (the ``AGN hypothesis''). We question this interpretation. We calculate the expected distribution of the arrival directions of cosmic rays under the AGN hypothesis and argue that it is not supported by the data, one of manifestations of the discrepancy being the deficit of events from the direction of the Virgo super…
There has been much interest in possible violations of Lorentz invariance, particularly motivated by quantum gravity theories. It has been suggested that a small amount of Lorentz invariance violation (LIV) could turn off photomeson interactions of ultrahigh energy cosmic rays (UHECRs) with photons of the cosmic background radiation and thereby eliminate the resulting sharp steepening in the spectrum of the highest energy CRs predicted by Greisen Zatsepin and Kuzmin (GZK). Recent measurements of the UHECR spectrum reported by the HiRes and Auger collaborations, however, indicate the presence o…
We introduce a static toy model of the cosmic ray (CR) universe in which cosmic ray propagation is taken to be diffusive and cosmic ray sources are distributed randomly with a density the same as that of local L* galaxies, $5 \times 10^{-3}$ Mpc$^{-3}$. These sources "fire" at random times through the history of the universe but with a set expectation time for the period between bursts. Our toy model model captures much of the essential CR physics despite its simplicity and, moreover, broadly reproduces CR phenomenology for reasonable parameter values and without extreme fine-tuning. Using thi…
The High Resolution Fly's Eye (HiRes) experiment is an air fluorescence detector which, operating in stereo mode, has a typical angular resolution of 0.6 degrees and is sensitive to cosmic rays with energies above 10^18 eV. HiRes is thus an excellent instrument for the study of the arrival directions of ultrahigh energy cosmic rays. We present the results of a search for anisotropies in the distribution of arrival directions on small scales (<5 degrees) and at the highest energies (>10^19 eV). The search is based on data recorded between 1999 December and 2004 January, with a total of 271 even…
We study the effect of the stochastic character of supernova explosions on the anisotropy of galactic cosmic rays below the knee. We conclude that if the bulk of cosmic rays are produced in supernova explosions the observed small and nearly energy independent amplitude of the anisotropy and its phase are to the large extent determined by the history of these explosions in the vicinity of the solar system, namely by the location and the age of the supernova remnants, within a few kpc, which give the highest contribution to the total intensity at the present epoch. Among the most important facto…
We show that ``top-down'' mechanisms of Ultra-High Energy Cosmic Rays which involve heavy relic particle-like objects predict Galactic anisotropy of highest energy cosmic rays at the level of minimum $\sim 20%$. This anisotropy is large enough to be either observed or ruled out in the next generation of experiments.
The Pierre Auger Southern Observatory in Argentina has begun taking data as it is being developed up to a final enclosed area of 3000 square kilometres. A key aspect of the project is to provide information on the origin of the highest energy cosmic rays through understanding the arrival directions of those particles. To avoid claims of a spurious anisotropy detection because trials have not been properly accounted, the Auger Collaboration has agreed 'a priori' to the analysis prescription presented here. It specifies the following: 1. The accumulation time for the (future) data set to be anal…
Planned space-based ultra-high-energy cosmic-ray detectors (TUS, JEM-EUSO and S-EUSO) are best suited for searches of global anisotropies in the distribution of arrival directions of cosmic-ray particles because they will be able to observe the full sky with a single instrument. We calculate quantitatively the strength of anisotropies associated with two models of the origin of the highest-energy particles: the extragalactic model (sources follow the distribution of galaxies in the Universe) and the superheavy dark-matter model (sources follow the distribution of dark matter in the Galactic ha…
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 searches for their signatures have limited their contribution to the UHECR flux to be subdominant, while the theoretical motivation for these searches remained strong: Topological defects are a generic consequence of Grand Unified Theories and superheavy particles are a creditable dark matter candidate. While Fermi/GLAST results should help to improve soon bounds…
The Ultra High Energy Cosmic Ray UHECR, by UHE neutrino-relic neutrino Z showering in Hot Dark Halos HDM, should exhibits an energy spectra and an anisotropy reflecting (also) the relic neutrino masses and their hierarchical HDM halo clustering. A twin light neutrino mass splitting may reflect to twin Z resonance and into a complex UHECR spectra modulation, a twin bump, at the edge at highest GZK energy cut-off. Each possible neutrino mass associates a characteristic dark halo size (galactic, local, Super Cluster) and its local anisotropy due to our peculiar position within that dark matter di…
The Pierre Auger Observatory is a multi-national project for research on ultra-high energy cosmic rays. The Southern Auger Observatory in Mendoza province, Argentina, is approaching completion in 2007 with an instrumented area of 3,000 km^2. It will accurately measure the spectrum and composition of ultra-high energy cosmic rays up to and beyond the predicted GZK feature. We are obtaining results on the energy spectrum, mass composition and distribution of arrival directions on the southern sky. The Northern Auger Observatory is designed to complete and extend the investigations begun in the S…
The present status of anisotropy studies for the highest energy cosmic rays is presented including the first full sky survey. Directions and prospects for the future are also discussed in light of new statistical methods and the last quantities of data expected in the near future from the Pierre Auger Observatory.
We measure the correlation between sky coordinates of the Swift BAT catalogue of active galactic nuclei with the arrival directions of the highest energy cosmic rays detected by the Auger Observatory. The statistically complete, hard X-ray catalogue helps to distinguish between AGN and other source candidates that follow the distribution of local large-scale structure. The positions of the full catalogue are marginally uncorrelated with the cosmic ray arrival directions, but when weighted by their hard X-ray flux, AGN within 100 Mpc are correlated at a significance level of 98 per cent. This c…
We have performed the detailed numerical simulations on the propagation of the UHE protons in the energy range $E=(10^{19.5} - 10^{22.0}$) eV in the relatively strong extra-galactic magnetic field with strength $B= (10, 100)$ nG within about 40 Mpc. In this case, the deflection angles of UHECRs become so large that the no counterparts problem is simply solved. As for the source distribution, we assumed that it is proportional to the number distribution of galaxies within the GZK sphere. We have found many clusters, which mean the small-scale anisotropy, in our simulations. It has been also sho…
Recent progress suggests we are moving towards a quantitative understanding of the whole cosmic ray spectrum, and that many bumps due to different components and processes hide beneath a relatively smooth total flux between knee and ankle. The knee is much better understood: the KASCADE observations support a rather sharp rigidity cut-off; while theoretical developments (strong magnetic field generation) indicate that supernova remnants (SNR) of different types should indeed accelerate to a very similar rigidity. X-ray and TeV observations of shell-type SNR produce evidence in favour of accele…
Decaying topological defects, in particular cosmic strings, can produce a significant flux of high energy neutrinos, photons and cosmic rays. According to the prevailing understanding of cosmic string dynamics in an expanding Universe, the network of long strings loses its energy first into string loops, which in turn give off most of their energy as gravitational radiation. However, it has been suggested by Vincent et al. (VHS) that particle emission may be the dominant energy loss channel for the long string network. In this case, the predicted flux of high energy particles would be much lar…
Using WMAP 3-year data at the locations of close to $\sim 700$ X-ray selected clusters we have detected the amplitude of the thermal Sunyaev-Zeldovich (TSZ) effect at the 15$σ$ level, the highest statistical significance reported so far. Owing to the large size of our cluster sample, we are able to detect the corresponding CMB distortions out to large cluster-centric radii. The region over which the TSZ signal is detected is, on average, four times larger in radius than the X-ray emitting region, extending to $\sim 3h_{70}^{-1}$Mpc. We show that an isothermal $β$ model does not fit the electro…
Ultra High Energy (UHE) particles coming from discrete extragalactic sources are potential candidates for EAS events above a few tens of EeV. In particular, galaxies with huge infrared luminosity triggered by collision and merging processes are possible sites of UHECR acceleration. Using the PSCz catalogue of IR galaxies we calculate a large scale anisotropy of UHE protons originating in the population of the luminous infrared galaxies (LIRGs). Small angle particle scattering in weak irregular extragalactic magnetic fields as well as deflection by regular Galactic field are taken into account.…
Contrary to earlier expectations, several cosmic ray events with energies above $10^{20}$ eV have been reported by a number of ultra-high energy cosmic ray observatories. According to the AGASA experiment, the flux of such events is well above the predicted Greisen-Zatsepin-Kuzmin cutoff due to the pion production of extragalactic cosmic ray protons off the cosmic microwave background. In addition to the relatively high flux of events, the isotropic distribution of arrival directions and an indication of small scale clustering strongly challenge all models proposed to resolve this puzzle. We d…
We have developed a model that explains cosmic rays with energies E between \~0.3 PeV and the energy of the second knee at E_2 ~ 3*10^{17} eV as originating from a recent Galactic gamma-ray burst (GRB) that occurred ~1 Myr ago within 1 kpc from Earth. Relativistic shocks from GRBs are assumed to inject power-law distributions of cosmic rays (CRs) to the highest energies. Diffusive propagation of CRs from the local GRB explains the CR spectrum near and above the first knee at E_1 ~ 3*10^{15} eV. The first and the second knees are explained as being directly connected with the injection of plasm…
The clustering properties of the highest energy cosmic rays and their correlations with candidate sources are re-examined using the most recently available AGASA data and a rigorous correlation analysis. The statistical methodology incorporates some important points not considered in previous studies. Results include small angle clustering significances consistent with, but somewhat less than, earlier findings, a possible large scale anisotropy for events with energies $E \approx 5 - 8 \times 10^{19} \mathrm{eV}$, and no statistically significant cross correlations with BL Lacertae or blazars.…
We consider the possibility that ultra-high energy cosmic rays originate from the annihilation of relic superheavy dark-matter particles. We find that a cross section of <sigma_A v> ~ 10^{-26}cm^2 (M_X/10^{12}GeV)^{3/2} is required to account for the observed rate of super-GZK events if the superheavy dark matter follows a Navarro-Frenk-White density profile. This would require extremely large-l contributions to the annihilation cross section. We also calculate the possible signature from annihilation in sub-galactic clumps of dark matter and find that the signal from sub-clumps dominates and …
During the recombination epoch, cosmic background photons couple not only to free electrons through Thompson scattering, but also to the neutral hydrogen through Rayleigh scattering. This latter is ~2% effect for photons near the peak of the photon energy distribution at z=800 and a ~0.2% effect at z=1100. Including Rayleigh scattering in the calculation reduces Silk damping at fixed redshift, alters the position of the surface of last scattering and alters the propagation of acoustic waves. We estimate the amplitude of these effects. For the Microwave Anisotropy Probe (MAP), Rayleigh scatteri…
