92 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
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
Global anisotropy of arrival directions of ultra-high-energy cosmic rays: capabilities of space-based detectors
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 halo). Based on
the expected exposure of the experiments, we estimate the optimal strategy for
efficient search of these effects.Comment: 19 pages, 7 figures, iopart style. v.2: discussion of the effect of
the cosmic magnetic fields added; other minor changes. Simulated UHECR
skymaps available at http://livni.inr.ac.ru/UHECRskymaps
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
Gamma-Ray Bursts and Magnetars as Possible Sources of Ultra High Energy Cosmic Rays: Correlation of Cosmic Ray Event Positions with IRAS Galaxies
We use the two-dimensional Kolmogorov-Smirnov (KS) test to study the
correlation between the 60 cosmic ray events above 4x10^19 eV from the AGASA
experiment and the positions of infrared luminous galaxies from the IRAS PSCz
catalog. These galaxies are expected to be hosts to gamma ray bursts (GRB) and
magnetars, both of which are associated with core collapse supernovae and have
been proposed as possible acceleration sites for ultra high energy cosmic rays.
We find consistency between the models and the AGASA events to have been drawn
from the same underlying distribution of positions on the sky with KS
probabilities ~50%. Application of the same test to the 11 highest AGASA events
above 10^20 eV, however, yields a KS probability of < 0.5%, rejecting the
models at >99.5% significance level. Taken at face value, these highest energy
results suggest that the existing cosmic ray events above 10^20 eV do not owe
their origin to long burst GRBs, rapidly rotating magnetars, or any other
events associated with core collapse supernovae. The larger data set expected
from the AUGER experiment will test whether this conclusion is real or is a
statistical fluke that we estimate to be at the 2 sigma level.Comment: 15 pages, 4 figures. Final Version to be published in Phys. Rev.
Anisotropy at the end of the cosmic ray spectrum?
The starburst galaxies M82 and NGC253 have been proposed as the primary
sources of cosmic rays with energies above eV. For energies \agt
10^{20.3} eV the model predicts strong anisotropies. We calculate the
probabilities that the latter can be due to chance occurrence. For the highest
energy cosmic ray events in this energy region, we find that the observed
directionality has less than 1% probability of occurring due to random
fluctuations. Moreover, during the first 5 years of operation at Auger, the
observation of even half the predicted anisotropy has a probability of less
than to occur by chance fluctuation. Thus, this model can be subject
to test at very small cost to the Auger priors budget and, whatever the outcome
of that test, valuable information on the Galactic magnetic field will be
obtained.Comment: Final version to be published in Physical Review
Highlights from the Pierre Auger Observatory
The Pierre Auger Observatory is the world's largest cosmic ray observatory.
Our current exposure reaches nearly 40,000 km str and provides us with an
unprecedented quality data set. The performance and stability of the detectors
and their enhancements are described. Data analyses have led to a number of
major breakthroughs. Among these we discuss the energy spectrum and the
searches for large-scale anisotropies. We present analyses of our X
data and show how it can be interpreted in terms of mass composition. We also
describe some new analyses that extract mass sensitive parameters from the 100%
duty cycle SD data. A coherent interpretation of all these recent results opens
new directions. The consequences regarding the cosmic ray composition and the
properties of UHECR sources are briefly discussed.Comment: 9 pages, 12 figures, talk given at the 33rd International Cosmic Ray
Conference, Rio de Janeiro 201
Astrophysical Origins of Ultrahigh Energy Cosmic Rays
In the first part of this review we discuss the basic observational features
at the end of the cosmic ray energy spectrum. We also present there the main
characteristics of each of the experiments involved in the detection of these
particles. We then briefly discuss the status of the chemical composition and
the distribution of arrival directions of cosmic rays. After that, we examine
the energy losses during propagation, introducing the Greisen-Zaptsepin-Kuzmin
(GZK) cutoff, and discuss the level of confidence with which each experiment
have detected particles beyond the GZK energy limit. In the second part of the
review, we discuss astrophysical environments able to accelerate particles up
to such high energies, including active galactic nuclei, large scale galactic
wind termination shocks, relativistic jets and hot-spots of Fanaroff-Riley
radiogalaxies, pulsars, magnetars, quasar remnants, starbursts, colliding
galaxies, and gamma ray burst fireballs. In the third part of the review we
provide a brief summary of scenarios which try to explain the super-GZK events
with the help of new physics beyond the standard model. In the last section, we
give an overview on neutrino telescopes and existing limits on the energy
spectrum and discuss some of the prospects for a new (multi-particle)
astronomy. Finally, we outline how extraterrestrial neutrino fluxes can be used
to probe new physics beyond the electroweak scale.Comment: Higher resolution version of Fig. 7 is available at
http://www.angelfire.com/id/dtorres/down3.html. Solicited review article
prepared for Reports on Progress in Physics, final versio
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