The energy region spanning from $\sim 10^{17}$ to $\lesssim 10^{19}$ eV is critical for understanding both, the Galactic and the extragalactic cosmic ray fluxes. This is the region where the propagation regime of nuclei inside the Galactic magnetic environment changes from diffusive to ballistic, as well as the region where, very likely, the most powerful Galactic accelerators reach their maximum output energies. In this work, a diffusion Galactic model is used to analyze the end of the Galactic cosmic ray spectrum and its mixing with the extragalactic cosmic ray flux. In particular, we study the conditions that must be met, from the spectral and composition points of view, by the Galactic and the extragalactic fluxes in order to reproduce simultaneously the total spectrum and elongation rate measured over the transition region by HiRes and Auger. Our analysis favors a mixed extragalactic spectrum in combination with a Galactic spectrum enhanced by additional high energy components, i.e., extending beyond the maximum energies expected from regular supernova remnants. The two additional components have mixed composition, with the lowest energy one heavier than the highest energy one. The potential impact on the astrophysical analysis of the assumed hadronic interaction model is also assessed in detail.
I present the analysis of data of astrophysical polarimetric observations that gives the signature of the fundamental extra dimension Planck scale magnitude essentially higher than $~1TeV$. Magnetic conversion of photons into the fundamental particles (scalars, gravitons) is the probable mechanism that can produce noticeable amount of polarization of optical radiation of astrophysical objects, especially, of distant extragalactic sources. The results of magnetic conversion process of optical light of extragalactic sources are presented for a number of situations including: (a) intergalactic ma…
Angular fluctuations of stochastic gravitational wave backgrounds (GWB) produced by extragalactic astrophysical sources are calculated. The angular properties of such backgrounds are determined by the large scale structure of Universe (galaxy clustering). The evolution of star formation rate with redshift is taken into account. Fluctuations of the metric strain amplitude associated with such noises at angular scales of about one degree are found to be of order 5-20% slowly growing toward smaller angular scales. This feature can be potentially used to separate astrophysical GWB from cosmologica…
The Lyon-Meudon Extragalactic database (LEDA) gives a free access to the main astrophysical parameters for more than 100,000 galaxies. The most common names are compiled allowing users to recover quickly any galaxy. All these measured astrophysical parameters are first reduced to a common system according to well defined reduction formulae leading to mean homogeneized parameters. Further, these parameters are also transformed into corrected parameters from widely accepted models. For instance, raw 21-cm line widths are transformed into mean standard widths after correction for instrumental eff…
The origin and chemical composition of ultra high energy cosmic rays is still an open question in astroparticle physics. The observed large-scale isotropy and also direct composition measurements can be interpreted as an extragalactic proton dominance above the ankle at about 10^10 GeV. Photopion production of extragalactic protons in the cosmic microwave background predicts a cutoff at about 5x10^10 GeV in conflict with excesses reported by some experiments. In this report we will outline a recent statistical analysis (astro-ph/0506698) of cosmic ray data using strongly interacting neutrinos …
We argue that the data published by the Pierre Auger Collaboration (arXiv:0711.2256) disfavor at 99% confidence level their hypothesis that most of the highest-energy cosmic rays are protons from nearby astrophysical sources, either Active Galactic Nuclei or other objects with a similar spatial distribution.
We discuss the region of transition between galactic and extragalactic cosmic rays. The exact shapes and compositions of these two components contains information about important parameters of powerful astrophysical sources and the conditions in extragalactic space. Several types of experimental data, including the exact shape of the ultrahigh energy cosmic rays, their chemical composition and their anisotropy, and the fluxes of cosmogenic neutrinos have to be included in the solution of this problem.
We present a quantitative analysis of the astrophysical and cosmological information that can be extracted from the many important wide-area, shallow surveys that will be carried out in the next few years. Our calculations combine the predictions of the physical model by Granato et al. (2004) for the formation and evolution of spheroidal galaxies with up-to-date phenomenological models for the evolution of starburst and normal late-type galaxies and of radio sources. We compute the expected number counts and the redshift distributions of these source populations separately and then focus on pr…
Confusion noise due to extragalactic sources is a fundamental astrophysical limitation for experiments aimed at accurately determining the power spectrum of the Cosmic Microwave Background (CMB) down to arcmin angular scales and with a sensitivity $ΔT/T \simeq 10^{-6}$. At frequencies $\lsim 200-300$ GHz, the most relevant extragalactic foreground hampering the detection of intrinsic CMB anisotropies is constituted by radio loud Active Galactic Nuclei (AGN), including ``flat--spectrum'' radiogalaxies, quasars, BL-LACs and blazars. We review our present understanding of astrophysical properties…
We consider the stochastic propagation of high-energy protons and nuclei in the cosmological microwave and infrared backgrounds, using revised photonuclear cross-sections and following primary and secondary nuclei in the full 2D nuclear chart. We confirm earlier results showing that the high-energy data can be fit with a pure proton extragalactic cosmic ray (EGCR) component if the source spectrum is $\propto E^{-2.6}$. In this case the ankle in the cosmic ray (CR) spectrum may be interpreted as a pair-production dip associated with the propagation. We show that when heavier nuclei are included…
I review the assumptions and observations that motivate the concept of the extragalactic cosmic background radiation, and the issues of energy accounts and star formation history as a function of galaxy morphological type that figure in the interpretation of the measurements of the extragalactic infrared background.
In order to facilitate the identification of possible new physics signatures in neutrino telescopes, such as neutrinos from the annihilation of neutralinos or decaying relics, it is essential to gain full control over the astrophysical inventory of neutrino sources in the Universe. The total available accretion power, the extragalactic gamma ray background, and the cosmic ray proton intensity can be used to constrain astrophysical models of neutrino production in extragalactic sources. The resulting upper limit on the extragalactic muon neutrino intensity from cosmic particle accelerators comb…
The apparent position of the "core" in a parsec-scale radio jet (a compact, bright emitting region at the narrow end of the jet) depends on the observing frequency, owing to synchrotron self-absorption and external absorption. While providing a tool probing physical conditions in the vicinity of the core, this dependency poses problems for astrometric studies using compact radio sources. We investigated the frequency-dependent shift in the positions of the cores (core shift) observed with very long baseline interferometry (VLBI) in parsec-scale jets. We discuss related physics, as well as its …
The contribution of an astrophysics group based in Milan to the science with the IUE satellite during its almost 20 years lifetime has focussed on high energy sources, of both galactic (LMXRB, HMXRB, and black hole candidates) and extragalactic (AGN) nature. The results of this long term research and in particular of the latest multiwavelength campaigns conducted simultaneously with IUE are reviewed here.
The energy losses and spectra of Ultra High Energy Cosmic Rays (UHECR) are calculated for protons as primary particles. The attention is given to the energy losses due to electron-positron production in collisions with the microwave 2.73 K photons. The energy spectra are calculated for several models, which differ by production spectra and by source distribution, namely: (i) Uniform distribution of the sources with steep generation spectra with indices 2.4 - 2.7, with cosmological evolution and without it. In this case it is possible to fit the shape of the observed spectrum up to 8.10^{19} eV…
Recent X-ray surveys have now resolved most of the X-ray background (XRB) into discrete sources. While this represents a break- through in the understanding of the XRB, the astrophysical nature of these sources still remains mysterious. In this article we present a sample of X-ray/optically selected extragalactic objects which are suitable for adaptive optics observations in the near infrared (NIR) at highest angu- lar resolution. The sample is based on a cross-correlation of the Sloan Digital Sky Survey and the ROSAT All Sky Survey. The NIR properties can help to disentangle the nature of the…
We extend previous studies of mixed-composition extragalactic cosmic-ray source models, by investigating the influence of a non-negligible extragalactic magnetic field on the propagated cosmic-ray spectrum and composition. We study the transport of charged particles in turbulent fields and the transition from a ballistic to a diffusive propagation regime. We introduce a method allowing a fast integration of the particle trajectories, which allows us to calculate extragalactic cosmic-ray spectra in the general case, without using either the diffusive or the rectilinear approximation. We find th…
High Velocity Clouds (HVCs) have recently attracted renewed attention as being long lived, massive dark matter dominated clouds of primordial composition distributed throughout the Local Group. In this picture the HVCs would contain a few times 10^7 M_sun of HI and would be at distances of a few hundred kpc to 1.5 Mpc from the Local Group barycenter. If this extragalactic interpretation of HVCs is true, similar clouds are expected in other galaxy groups and around galaxies. We discuss the limits blind HI surveys and QSO absorption line studies put on this proposed population of clouds.
We consider various classes of persistent extragalactic astrophysical sources which have been suggested in literature as possible emitters of ultra-high-energy cosmic rays (UHECR). We compare the strength of the claimed correlations by a uniform procedure for all classes of sources by making use of the AGASA, Yakutsk and HiRes stereo data. BL Lac type objects correlate with the cosmic rays detected by all three independent experiments and are more probably, compared to other astrophysical sources, related to the UHECR origin. With the account of the Galactic magnetic field (not possible for th…
A model for high-energy (>10^14 eV) cosmic rays (HECRs) from galactic and extragalactic gamma-ray bursts (GRBs) is summarized. Relativistic outflows in GRBs are assumed to inject power-law distributions of CR protons and ions to the highest (>10^20 eV) energies. A diffusive propagation model for HECRs from a single recent GRB within 1 kpc from Earth explains the CR spectrum near and above the knee. The CR spectrum at energies above 10^18 eV is fit with a component from extragalactic GRBs. By normalizing the energy injection rate to that required to produce the CR flux from extragalactic source…
We present spectra of the inverse-Compton and extragalactic components of the high-energy gamma-radiation based on an analysis of the emission at high galactic latitudes ($\vert$b$\vert$ $\geq$ $30°$). We correlate the gamma-ray intensity with a model consisting of an isotropic component, a component proportional to the 408 MHz synchrotron radiation, and a component proportional to atomic hydrogen (H I) column density with different emissivities in eight galactic octants. The spectrum of gamma-radiation that is correlated with the H I column density indicates that this component originates in …
Mainstream presolar SiC grains from primitive meteorites show a clear s-process signature in the isotopic composition of heavy trace elements. These grains most likely condensed in the winds of a variety of AGB stars. However, the non-solar and correlated Si and Ti isotopic compositions measured in these grains are inconsistent with a pure s-signature. We present a possible solution to this much-discussed problem by assuming a spread in the original composition of parent AGB stars due to small chemical inhomogeneities in the interstellar medium at the time of their birth. These inhomogeneities…
A variety of observations suggest that magnetic fields are present in all galaxies and galaxy clusters. These fields are characterized by a modest strength (10^{-7}-10^{-5} G) and huge spatial scale (~Mpc). It is generally assumed that magnetic fields in spiral galaxies arise from the combined action of differential rotation and helical turbulence, a process known as the alpha-omega dynamo. However fundamental questions concerning the nature of the dynamo as well as the origin of the seed fields necessary to prime it remain unclear. Moreover, the standard alpha-omega dynamo does not explain th…
Many galactic and extragalactic astrophysical sources are currently considered promising candidates as high energy neutrino emitters. Astrophysical neutrinos can be detected as upward-going muons produced in charged-current interactions with the medium surrounding the detector. The expected neutrino fluxes from various models start to dominate on the atmospheric neutrino background at neutrino energies above some tens of TeV. We present the results of a search for an excess of high energy upward-going muons among the sample of data collected by MACRO during ~5.8 years of effective running time…
We discuss the region of transition between galactic and extragalactic cosmic rays. The exact shapes and compositions of these two components contains information about important parameters of powerful astrophysical sources and the conditions in extragalactic space as well as for the cosmological evolution of the sources of high energy cosmic rays. Several types of experimental data, including the exact shape of the ultrahigh energy cosmic rays, their chemical composition and their anisotropy, and the fluxes of cosmogenic neutrinos have to be included in the solution of this problem.
Ongoing experimental efforts to detect cosmic sources of high energy neutrinos are guided by the expectation that astrophysical accelerators of cosmic ray protons would also generate neutrinos through interactions with ambient matter and/or photons. However there will be a reduction in the predicted neutrino flux if cosmic ray sources accelerate not only protons but also significant number of heavier nuclei, as is indicated by recent air shower data. We consider plausible extragalactic sources such as active galactic nuclei, gamma-ray bursts and starburst galaxies and demand consistency with t…
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…
I give a brief critical review of the predicted intensity of diffuse high energy neutrinos of astrophysical origin over the energy range from 10^12 eV to 10^24 eV. Neutrinos from interactions of galactic cosmic rays with interstellar matter are guaranteed, and the intensity can be reliably predicted to within a factor of about 2 up to 10^17 eV. Somewhat less certain are intensities in the same energy range from cosmic rays escaping from normal galaxies or active galactic nuclei (AGN) and interacting with intracluster gas. At higher energies, neutrinos will be produced by interactions of extrag…
The study of the Extragalactic Background Light (EBL) is crucial to understand many astrophysical problems (as the formation of first stars, the evolution of galaxies and the role of dust emission). At present, one of the most powerful ways to put constraints on EBL is represented by the study of the photon-photon absorption on gamma-ray spectra of TeV blazars. Adopting this method, we found that, if the only contribution to the optical and Near Infrared (NIR) background is given by galaxies, the spectrum of the blazar H1426+428 cannot be fitted. To reproduce the observational data of H1426+42…
The diffuse extragalactic gamma-ray background (EGRB) has been derived by various groups from observations by the Energetic Gamma Ray Experiment Telescope (EGRET) instrument on the Compton Gamma Ray Observatory (CGRO). The derived EGRB consists of gamma rays that may come from astrophysical components, such as from unresolved extragalactic point sources (blazars, normal galaxies, etc.), true extragalactic diffuse emission, misattributed diffuse signals from the Galaxy and other celestial sources, and an irreducible instrumental background due to gamma rays produced by cosmic-ray (CR) interacti…
A substantial increase of the mean logarithmic mass $<\ln A>$ of galactic cosmic rays {\em vs} energy has been observed . We study three effects that could explain this trend i) different source spectra for protons and heavy nuclei ii) a selective nuclear destruction in flight of heavies iii) a gradient of the source number and chemical composition in the galactic disk. We take advantage of the diffusive cosmic ray propagation model developed at LAPTH to study specifically the geometrical aspects of the propagation and extend it to high energy. Using a simple modeling of the spectral knee arou…
Several recent papers claim the detection of a near infrared Extragalactic Background Light (EBL) intensity at 1.25 - 4 um that exceeds the integrated light of galaxies by factors of >3. When combined with a claimed optical detection of the EBL at 0.80 um the EBL excess emission spectrum has a discontinuity at ~1 um. This discontinuity has given rise to an interpretation in terms of ultraviolet radiation emanating from the first generation of massive stars at redshifts of 7 - 20 (so called Population III stars). The interpretation of the NIR excess emission as being of extragalactic origin dep…
We use the new results of the HEGRA detector on the TeV gamma-ray emission from MKN 501 to set upper limits on the energy density of the cosmic infrared background (CIRB). Contrary to previous interpretations of the gamma-ray spectrum of MKN 421 as showing an intergalactic absorption cutoff at 5 TeV, the observed spectrum of MKN 501 extends beyond 10 TeV and appears to be unattenuated by gamma-gamma collisions with the low-energy CIRB photons. The upper limits on the CIRB intensity -- derived both assuming an `a priori' shape for the CIRB spectrum and without model-dependent assumptions -- are…
We briefly discuss three aspects related to the origin of ultra-high energy cosmic rays (UHECRs) namely: 1) particle acceleration in astrophysical sources; 2) transition to an extragalactic origin; 3) spectrum and anisotropies at the highest energies.
The Z-burst mechanism invoked to explain ultra-high energy cosmic rays is severely constrained by measurements of the cosmic gamma-ray background by EGRET. We discuss the case of optically thick sources and show that jets and hot spots of active galaxies cannot provide the optical depth required to suppress the photon flux. Other extragalactic accelerators (AGN cores and sites of gamma ray bursts), if they are optically thick, could be tested by future measurements of the secondary neutrino flux.
The High Energy Stereoscopic System (H.E.S.S.) experiment, a ground-based gamma-ray Cherenkov telescope array located in Namibia, has now detected many extragalactic objects, which redshifts range from z=0.00183 up to z=0.2, possibly more. With the increasing performances of Cherenkov telescopes, it now becomes possible to probe these objects at small timescales in gamma-ray, allowing the study of regions thought to be very close to the central supermassive black holes. Furthermore, H.E.S.S. has confirmed a gamma-ray emission from M87, which is thus the first extragalactic source seen at the T…
The next generation of ultra high energy cosmic ray experiments will probably detect several dozens of events clustered around the direction towards each of the most powerful extragalactic sources. We develop a method which could make possible to reconstruct, from the arrival directions and energies of the clustered events, the strength and coherence properties of the magnetic field along the line of sight towards the sources. The method exploits peculiar signatures arising from magnetic lensing effects, such as the strong flux magnification of multiple images around caustics. We also discuss …
Primordial Black Holes (PBH) may have formed from the collapse of cosmic string loops. The spectral shape of the PBH mass spectrum can be determined by the scaling argument for string networks. Limits on the spectral amplitude derived from extragalactic gamma-ray and galactic gamma-ray and cosmic ray flux observations as well as constraints from the possible formation of stable black holes remnants are reanalyzed. The new constraints are remarkably close to those derived from the normalization of the cosmic string model to the cosmic microwave background anisotropies.
We compare the clustering properties of the combined dataset of ultra-high energy cosmic rays events, reported by the AGASA, HiRes, Yakutsk and Sugar collaborations, with a catalogue of galaxies of the local universe (redshift z<~0.06). We find that the data reproduce particularly well the clustering properties of the nearby universe within z <~0.02. There is no statistically significant cross-correlation between data and structures, although intriguingly the nominal cross-correlation chance probability drops from ~50% to ~10% using the catalogue with a smaller horizon. Also, we discuss the im…
In a recent paper, Waxman and Bahcall (PRD 59, 023002) claimed that the present data on ultra-high energy cosmic rays imply a model-independent upper bound on extragalactic neutrino fluxes of 2*10^-8 GeV cm^-2 s^-1 ster^-1, independent of neutrino energy. Mannheim, Protheroe and Rachen (astro-ph/9812398) have repeated this calculation and confirmed the WB-bound, within a factor of 2, only at a very limited energy range of E_ν\sim 10^(16-18) eV, while at other energies the neutrino flux is mainly limited by the extragalactic gamma ray background to a level about two orders of magnitude higher t…
Constraints on the lifetime of the heavy sterile neutrino, that was proposed as a possible interpretation of the KARMEN anomaly, are derived from primordial nucleosynthesis and SN 1987A. Together with the recent experimental bounds on the nu_s lifetime, SN 1987A completely excludes this interpretation. Nucleosynthesis arguments permit a narrow window for the lifetime in the interval 0.1-0.2 sec. If nu_s possesses an anomalous interaction with nucleons, the SN bounds may not apply, while the nucleosynthesis ones would remain valid.
We elucidate the physical basis for the upper bound on high energy neutrino fluxes implied by the observed cosmic ray flux. We stress that the bound is valid for neutrinos produced either by p,gamma reactions or by p-p(n) reactions in sources which are optically thin for high energy protons to photo-meson and nucleon-meson interactions. We show that the upper bound is robust and conservative. The Waxman-Bahcall bound overestimates the most likely neutrino flux by a factor ~ 5/tau, for small optical depths tau. The upper limit cannot be plausibly evaded by invoking magnetic fields, optically th…
Recently, several interesting proposals were made modifying the law of gravity on large scales, within a sensible relativistic formulation. This allows a precise formulation of the idea that such a modification might account for galaxy rotation curves, instead of the usual interpretation of these curves as evidence for dark matter. We here summarize several observational constraints which any such modification must satisfy, and which we believe make more challenging any interpretation of galaxy rotation curves in terms of new gravitational physics.
