117 research outputs found
Correlations between Ultrahigh Energy Cosmic Rays and Infrared-Luminous Galaxies
We confirm the UHECR horizon established by the Pierre Auger Observatory
using the heterogeneous Veron-Cetty Veron (VCV) catalog of AGNs, by performing
a redshift-angle-IR luminosity scan using PSCz galaxies having infrared
luminosity greater than 10^{10}L_sun. The strongest correlation -- for z <
0.016, psi = 2.1 deg, and L_ir > 10^{10.5}L_sun -- arises in fewer than 0.3% of
scans with isotropic source directions. When we apply a penalty for using the
UHECR energy threshold that was tuned to maximize the correlation with VCV, the
significance degrades to 1.1%. Since the PSCz catalog is complete and
volume-limited for these parameters, this suggests that the UHECR horizon
discovered by the Pierre Auger Observatory is not an artifact of the
incompleteness and other idiosyncrasies of the VCV catalog. The strength of the
correlation between UHECRs and the nearby highest-IR-luminosity PSCz galaxies
is stronger than in about 90% percent of trials with scrambled luminosity
assignments for the PSCz galaxies. If confirmed by future data, this result
would indicate that the sources of UHECRs are more strongly associated with
luminous IR galaxies than with ordinary, lower IR luminosity galaxies.Comment: 4 pages, 3 figures. Replaced with accepted versio
UHECR observations and lensing in the magnetic field of the Virgo cluster
We discuss how lensing by magnetic fields in galaxy clusters affects
ultrahigh energy cosmic ray (UHECR) observations. As specific example, we use
Virgo together with the cluster magnetic fields obtained earlier in a
constrained simulation of structure formation including MHD processes. We find
that, if M87 is the single source of UHECRs from Virgo, the emitted flux is
strongly anisotropic in the most interesting energy range, (50-100)EeV, and
differs from the average value by a factor five or more for a significant
fraction of observers. Since magnetic lensing is energy dependent, the external
energy spectrum as seen by different observers varies strongly too. These
anisotropies are averaged out in the case that all active galactic nuclei in
Virgo emit UHECRs. In both cases, the anisotropies of the emitted UHECR flux
may introduce an important bias in the interpretation of UHECR data like, e.g.,
the determination of the source density n_s and the source energy spectrum of
UHECRs.Comment: 12 pages, 15 eps figures; v2: extended discussion of modifications in
external energy spectrum, matches version to be publishe
UHECR Anisotropy from Luminous Infrared Galaxies - Predictions for the Pierre Auger Observatory
Abstract We consider the hypothesis that luminous infrared galaxies (LIRGs) are sources of the UHECRs. By associating the AGASA triplet with the Arp 299 galaxy we obtain reasonable values for Galactic and extragalactic magnetic fields. We predict what the southern sky, to be seen by the Auger experiment, should look like, so that the LIRG hypothesis could be verified soon
Search for single sources of ultra high energy cosmic rays on the sky
In this paper, we suggest a new way to identify single bright sources of
Ultra High Energy Cosmic Rays (UHECR) on the sky, on top of background. We look
for doublets of events at the highest energies, E > 6 x 10^19 eV, and identify
low energy tails, which are deflected by the Galactic Magnetic Field (GMF). For
the sources which are detected, we can recover their angular positions on the
sky within one degree from the real ones in 68% of cases. The reconstruction of
the deflection power of the regular GMF is strongly affected by the value of
the turbulent GMF. For typical values of 4 microG near the Earth, one can
reconstruct the deflection power with 25% precision in 68% of cases.Comment: 20 pages, 10 figures. Corresponds to the version published in JCA
Magnetic deflections and possible sources of the ultra-high-energy cosmic rays in the AGASA-HiRes-Yakutsk cluster
The cluster of ultra-high-energy cosmic rays observed by the AGASA, HiRes and
Yakutsk experiments is studied with respect to possible deflections of
particles in regular magnetic fields. Best-fit positions of a potential source
of these clustered particles are found, with account of the errors in energy
estimation, both in the frameworks of particular models of the Galactic
magnetic field and treating the direction and the amount of deflection as free
parameters. The study suggests that an unknown regular component of either
Galactic or extragalactic magnetic field may dominate over modelled components
in the direction of the cluster. Possible sources of the cosmic rays in that
direction are considered.Comment: 18 pages, 3 eps figures, iopart.cl
Clusters of Galaxies and the Diffuse Gamma Ray Background
We discuss the diffuse emission of gamma rays and neutrinos from galaxy
clusters in the viable models for structure formation in the universe. We use a
self-consistent picture for cluster formation and evolution starting from a
primordial density perturbation spectrum, and a realistic modelling for the
distribution of the intergalactic medium which is abundantly present within
galaxy clusters. We find that an evolving population of clusters can produce a
fraction of the diffuse gamma-ray background (DGRB)
observed by EGRET. This result is robust and is weakly dependent on the
cosmological scenario and on the degree of evolution of the inter galactic
medium (IGM) in distant clusters, because the bulk of the sources contributing
to the DGRB is located at redshifts z \simlt 0.2. We also found a correlation
between the non-thermal, gamma-ray and the thermal X-ray emissions from these
structures. Using this result, we derived a list of gamma-ray clusters
observable with the next generation -ray detectors. Finally, we briefly
discuss the possible relevance of galaxy clusters for neutrino astronomy and
for very high energy particle astronomy.Comment: 37 pages, 9 Figures, Latex (using elsart,epsfig), to appear in
Astroparticle Physics. Send comments to S.Colafrancesco:
[email protected]
The signature of local cosmic structures on the ultra-high energy cosmic ray anisotropies
Current experiments collecting high statistics in ultra-high energy cosmic
rays (UHECRs) are opening a new window on the universe facing the possibility
to perform UHECR astronomy. Here we discuss a large scale structure (LSS) model
for the UHECR origin for which we evaluate the expected large scale anisotropy
in the UHECR arrival distribution. Employing the IRAS PSCz catalogue as tracer
of the LSS, we derive the minimum statistics needed to reject or assess the
correlation of the UHECRs with the baryonic distribution in the universe, in
particular providing a forecast for the Auger experiment.Comment: 8 pages, 6 figures, contribution to the CRIS06 proceedings (Catania,
Italy, May 29 - June 2, 2006
Cross-Correlation between UHECR Arrival Distribution and Large-Scale Structure
We investigate correlation between the arrival directions of
ultra-high-energy cosmic rays (UHECRs) and the large-scale structure (LSS) of
the Universe by using statistical quantities which can find the angular scale
of the correlation. The Infrared Astronomical Satellite Point Source Redshift
Survey (IRAS PSCz) catalog of galaxies is adopted for LSS. We find a positive
correlation of the highest energy events detected by the Pierre Auger
Observatory (PAO) with the IRAS galaxies inside within the angular
scale of . This positive correlation observed in the southern
sky implies that a significant fraction of the highest energy events comes from
nearby extragalactic objects. We also analyze the data of the Akeno Giant Air
Shower Array (AGASA) which observed the northern hemisphere, but the obvious
signals of positive correlation with the galaxy distribution are not found.
Since the exposure of the AGASA is smaller than the PAO, the cross-correlation
in the northern sky should be tested using a larger number of events detected
in the future. We also discuss the correlation using the all-sky combined data
sets of both the PAO and AGASA, and find a significant correlation within . These angular scales can constrain several models of intergalactic
magnetic field. These cross-correlation signals can be well reproduced by a
source model in which the distribution of UHECR sources is related to the IRAS
galaxies.Comment: 21 pages,7 figure
- …