10 research outputs found
Search for microwave emission from ultrahigh energy cosmic rays
We present a search for microwave emission from air showers induced by
ultrahigh energy cosmic rays with the microwave detection of air showers
experiment. No events were found, ruling out a wide range of power flux and
coherence of the putative emission, including those suggested by recent
laboratory measurements.Comment: 5 pages, 3 figure
Anisotropy and chemical composition of ultra-high energy cosmic rays using arrival directions measured by the Pierre Auger Observatory
The Pierre Auger Collaboration has reported evidence for anisotropy in the
distribution of arrival directions of the cosmic rays with energies
eV. These show a correlation with the distribution
of nearby extragalactic objects, including an apparent excess around the
direction of Centaurus A. If the particles responsible for these excesses at
are heavy nuclei with charge , the proton component of the
sources should lead to excesses in the same regions at energies . We here
report the lack of anisotropies in these directions at energies above
(for illustrative values of ). If the anisotropies
above are due to nuclei with charge , and under reasonable
assumptions about the acceleration process, these observations imply stringent
constraints on the allowed proton fraction at the lower energies
Precise measurement of the absolute fluorescence yield of the 337 nm band in atmospheric gases
Contains fulltext :
111214.pdf (preprint version ) (Open Access
Application of Dynamic Mechanical Analysis (DMA) to the determination of the mechanical properties of coated pellets
The Surface Detector of the Pierre Auger Observatory is sensitive to neutrinos of all flavors above 0.1 EeV. These interact through charged and neutral currents in the atmosphere giving rise to extensive air showers. When interacting deeply in the atmosphere at nearly horizontal incidence, neutrinos can be distinguished from regular hadronic cosmic rays by the broad time structure of their shower signals in the water-Cherenkov detectors. In this paper we present for the first time an analysis based on down-going neutrinos. We describe the search procedure, the possible sources of background, the method to compute the exposure and the associated systematic uncertainties. No candidate neutrinos have been found in data collected from 1 January 2004 to 31 May 2010. Assuming an E-2 differential energy spectrum the limit on the single-flavor neutrino is E2dN/dE<1.74×10-7GeVcm-2s-1sr-1 at 90% C.L. in the energy range 1×1017e
The effect of the geomagnetic field on cosmic ray energy estimates and large scale anisotropy searches on data from the Pierre Auger Observatory
We present a comprehensive study of the influence of the geomagnetic field on
the energy estimation of extensive air showers with a zenith angle smaller than
, detected at the Pierre Auger Observatory. The geomagnetic field
induces an azimuthal modulation of the estimated energy of cosmic rays up to
the ~2% level at large zenith angles. We present a method to account for this
modulation of the reconstructed energy. We analyse the effect of the modulation
on large scale anisotropy searches in the arrival direction distributions of
cosmic rays. At a given energy, the geomagnetic effect is shown to induce a
pseudo-dipolar pattern at the percent level in the declination distribution
that needs to be accounted for.Comment: 20 pages, 14 figure
Correlation of the highest-energy cosmic rays with nearby extragalactic objects
Using data collected at the Pierre Auger Observatory during the past 3.7 years, we demonstrated a correlation between the arrival directions of cosmic rays with energy above 6 × 1019 electron volts and the positions of active galactic nuclei (AGN) lying within ∼75 megaparsecs. We rejected the hypothesis of an isotropic distribution of these cosmic rays with at least a 99% confidence level from a prescribed a priori test. The correlation we observed is compatible with the hypothesis that the highest-energy particles originate from nearby extragalactic sources whose flux has not been substantially reduced by interaction with the cosmic background radiation. AGN or objects having a similar spatial distribution are possible sources
Correlation of the Highest-energy Cosmic Rays with the Positions of Nearby Active Galactic Nuclei.
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
hypothesis that cosmic rays with the highest energies originate from
extra-galactic sources close enough so that their flux is not significantly
attenuated by interaction with the cosmic background radiation (the
Greisen-Zatsepin-Kuz'min effect). The angular scale of the correlation observed
is a few degrees, which suggests a predominantly light composition unless the
magnetic fields are very weak outside the thin disk of our galaxy. Our present
data do not identify AGN as the sources of cosmic rays unambiguously, and other
candidate sources which are distributed as nearby AGN are not ruled out. We
discuss the prospect of unequivocal identification of individual sources of the
highest-energy cosmic rays within a few years of continued operation of the
Pierre Auger Observatory.Comment: 33 pages, 8 figures, submitted to Astropart. phys. Now match the
published versio
Upper limit on the cosmic-ray photon fraction at EeV energies from the Pierre Auger Observatory
From direct observations of the longitudinal development of ultra-high energy air showers performed with the Pierre Auger Observatory, upper limits of 3.8%, 2.4%, 3.5% and 11.7% (at 95% c.l.) are obtained on the fraction of cosmic-ray photons above 2, 3, 5 and 10 EeV, respectively. These are the first experimental limits on ultra-high energy photons at energies below 10 EeV. The results complement previous constraints on top–down models from array data and they reduce systematic uncertainties in the interpretation of shower data in terms of primary flux, nuclear composition and proton-air cross-section
Correlation of the highest energy cosmic rays with nearby extragalactic objects
Using data collected at the Pierre Auger Observatory during the past 3.7 years, we demonstrated a correlation between the arrival directions of cosmic rays with energy above 6 × 10^19 electron volts and the positions of active galactic nuclei (AGN) lying within ~75 megaparsecs. We rejected the hypothesis of an isotropic distribution of these cosmic rays with at least a 99% confidence level from a prescribed a priori test. The correlation we observed is compatible with the hypothesis that the highest-energy particles originate from nearby extragalactic sources whose flux has not been substantially reduced by interaction with the cosmic background radiation. AGN or objects having a similar
spatial distribution are possible sources