Abstract The flux of ultra-high energy cosmic rays reaching Earth above the ankle energy (5 EeV) can be described as a mixture of nuclei injected by extragalactic sources with very hard spectra and a ...low rigidity cutoff. Extragalactic magnetic fields existing between the Earth and the closest sources can affect the observed CR spectrum by reducing the flux of low-rigidity particles reaching Earth. We perform a combined fit of the spectrum and distributions of depth of shower maximum measured with the Pierre Auger Observatory including the effect of this magnetic horizon in the propagation of UHECRs in the intergalactic space. We find that, within a specific range of the various experimental and phenomenological systematics, the magnetic horizon effect can be relevant for turbulent magnetic field strengths in the local neighbourhood in which the closest sources lie of order B rms ≃ (50–100) nG (20 Mpc/d s )( 100 kpc/L coh ) 1/2 , with d s the typical intersource separation and L coh the magnetic field coherence length. When this is the case, the inferred slope of the source spectrum becomes softer and can be closer to the expectations of diffusive shock acceleration, i.e., ∝ E -2 . An additional cosmic-ray population with higher source density and softer spectra, presumably also extragalactic and dominating the cosmic-ray flux at EeV energies, is also required to reproduce the overall spectrum and composition results for all energies down to 0.6 EeV.
Ultra-high-energy photons with energies exceeding 1017 eV offer a wealth of connections to different aspects of cosmic-ray astrophysics as well as to gamma-ray and neutrino astronomy. The recent ...observations of photons with energies in the 1015 eV range further motivate searches for even higher-energy photons. In this paper, we present a search for photons with energies exceeding 2 × 1017 eV using about 5.5 yr of hybrid data from the low-energy extensions of the Pierre Auger Observatory. The upper limits on the integral photon flux derived here are the most stringent ones to date in the energy region between 1017 and 1018 eV.
The flux of ultra-high energy cosmic rays reaching Earth above the ankle energy (5 EeV) can be described as a mixture of nuclei injected by extragalactic sources with very hard spectra and a low ...rigidity cutoff. Extragalactic magnetic fields existing between the Earth and the closest sources can affect the observed CR spectrum by reducing the flux of low-rigidity particles reaching Earth. We perform a combined fit of the spectrum and distributions of depth of shower maximum measured with the Pierre Auger Observatory including the effect of this magnetic horizon in the propagation of UHECRs in the intergalactic space. We find that, within a specific range of the various experimental and phenomenological systematics, the magnetic horizon effect can be relevant for turbulent magnetic field strengths in the local neighbourhood of order \(B_{\rm rms}\simeq (50-100)\,{\rm nG}\,(20\rm{Mpc}/{d_{\rm s})( 100\,\rm{kpc}/L_{\rm coh}})^{1/2}\), with \(d_{\rm s}\) the typical intersource separation and \(L_{\rm coh}\) the magnetic field coherence length. When this is the case, the inferred slope of the source spectrum becomes softer and can be closer to the expectations of diffusive shock acceleration, i.e., \(\propto E^{-2}\). An additional cosmic-ray population with higher source density and softer spectra, presumably also extragalactic and dominating the cosmic-ray flux at EeV energies, is also required to reproduce the overall spectrum and composition results for all energies down to 0.6~EeV.
Ultra-high-energy cosmic rays are known to be mainly of extragalactic origin, and their propagation is limited by energy losses, so their arrival directions are expected to correlate with the ...large-scale structure of the local Universe. In this work, we investigate the possible presence of intermediate-scale excesses in the flux of the most energetic cosmic rays from the direction of the supergalactic plane region using events with energies above 20 EeV recorded with the surface detector array of the Pierre Auger Observatory up to 31 December 2022, with a total exposure of 135,000 km^2 sr yr. The strongest indication for an excess that we find, with a post-trial significance of 3.1{\sigma}, is in the Centaurus region, as in our previous reports, and it extends down to lower energies than previously studied. We do not find any strong hints of excesses from any other region of the supergalactic plane at the same angular scale. In particular, our results do not confirm the reports by the Telescope Array collaboration of excesses from two regions in the Northern Hemisphere at the edge of the field of view of the Pierre Auger Observatory. With a comparable exposure, our results in those regions are in good agreement with the expectations from an isotropic distribution.
The Pierre Auger Collaboration has embraced the concept of open access to their research data since its foundation, with the aim of giving access to the widest possible community. A gradual process ...of release began as early as 2007 when 1% of the cosmic-ray data was made public, along with 100% of the space-weather information. In February 2021, a portal was released containing 10% of cosmic-ray data collected from 2004 to 2018, during Phase I of the Observatory. The Portal included detailed documentation about the detection and reconstruction procedures, analysis codes that can be easily used and modified and, additionally, visualization tools. Since then the Portal has been updated and extended. In 2023, a catalog of the 100 highest-energy cosmic-ray events examined in depth has been included. A specific section dedicated to educational use has been developed with the expectation that these data will be explored by a wide and diverse community including professional and citizen-scientists, and used for educational and outreach initiatives. This paper describes the context, the spirit and the technical implementation of the release of data by the largest cosmic-ray detector ever built, and anticipates its future developments.
The Pierre Auger Observatory is the most sensitive instrument to detect photons with energies above \(10^{17}\) eV. It measures extensive air showers generated by ultra high energy cosmic rays using ...a hybrid technique that exploits the combination of a fluorescence detector with a ground array of particle detectors. The signatures of a photon-induced air shower are a larger atmospheric depth of the shower maximum (\(X_{max}\)) and a steeper lateral distribution function, along with a lower number of muons with respect to the bulk of hadron-induced cascades. In this work, a new analysis technique in the energy interval between 1 and 30 EeV (1 EeV = \(10^{18}\) eV) has been developed by combining the fluorescence detector-based measurement of \(X_{max}\) with the specific features of the surface detector signal through a parameter related to the air shower muon content, derived from the universality of the air shower development. No evidence of a statistically significant signal due to photon primaries was found using data collected in about 12 years of operation. Thus, upper bounds to the integral photon flux have been set using a detailed calculation of the detector exposure, in combination with a data-driven background estimation. The derived 95% confidence level upper limits are 0.0403, 0.01113, 0.0035, 0.0023, and 0.0021 km\(^{-2}\) sr\(^{-1}\) yr\(^{-1}\) above 1, 2, 3, 5, and 10 EeV, respectively, leading to the most stringent upper limits on the photon flux in the EeV range. Compared with past results, the upper limits were improved by about 40% for the lowest energy threshold and by a factor 3 above 3 EeV, where no candidates were found and the expected background is negligible. The presented limits can be used to probe the assumptions on chemical composition of ultra-high energy cosmic rays and allow for the constraint of the mass and lifetime phase space of super-heavy dark matter particles.
We test the predictions of hadronic interaction models regarding the depth of maximum of air-shower profiles, \(X_{max}\), and ground-particle signals in water-Cherenkov detectors at 1000 m from the ...shower core, \(S(1000)\), using the data from the fluorescence and surface detectors of the Pierre Auger Observatory. The test consists in fitting the measured two-dimensional (\(S(1000)\), \(X_{max}\)) distributions using templates for simulated air showers produced with hadronic interaction models EPOS-LHC, QGSJet II-04, Sibyll 2.3d and leaving the scales of predicted \(X_{max}\) and the signals from hadronic component at ground as free fit parameters. The method relies on the assumption that the mass composition remains the same at all zenith angles, while the longitudinal shower development and attenuation of ground signal depend on the mass composition in a correlated way. The analysis was applied to 2239 events detected by both the fluorescence and surface detectors of the Pierre Auger Observatory with energies between \(10^{18.5}\) to \(10^{19.0}\) eV and zenith angles below \(60^\circ\). We found, that within the assumptions of the method, the best description of the data is achieved if the predictions of the hadronic interaction models are shifted to deeper \(X_{max}\) values and larger hadronic signals at all zenith angles. Given the magnitude of the shifts and the data sample size, the statistical significance of the improvement of data description using the modifications considered in the paper is larger than \(5\sigma\) even for any linear combination of experimental systematic uncertainties.
Dark matter particles could be superheavy, provided their lifetime is much longer than the age of the universe. Using the sensitivity of the Pierre Auger Observatory to ultra-high energy neutrinos ...and photons, we constrain a specific extension of the Standard Model of particle physics that meets the lifetime requirement for a superheavy particle by coupling it to a sector of ultra-light sterile neutrinos. Our results show that, for a typical dark coupling constant of 0.1, the mixing angle \(\theta_m\) between active and sterile neutrinos must satisfy, roughly, \(\theta_m \lesssim 1.5\times 10^{-6}(M_X/10^9~\mathrm{GeV})^{-2}\) for a mass \(M_X\) of the dark-matter particle between \(10^8\) and \(10^{11}~\)GeV.
We present measurements of the atmospheric depth of the shower maximum
$X_\mathrm{max}$, inferred for the first time on an event-by-event level using
the Surface Detector of the Pierre Auger ...Observatory. Using deep learning, we
were able to extend measurements of the $X_\mathrm{max}$ distributions up to
energies of 100 EeV ($10^{20}$ eV), not yet revealed by current measurements,
providing new insights into the mass composition of cosmic rays at extreme
energies. Gaining a 10-fold increase in statistics compared to the Fluorescence
Detector data, we find evidence that the rate of change of the average
$X_\mathrm{max}$ with the logarithm of energy features three breaks at
$6.5\pm0.6~(\mathrm{stat})\pm1~(\mathrm{sys})$ EeV, $11\pm
2~(\mathrm{stat})\pm1~(\mathrm{sys})$ EeV, and
$31\pm5~(\mathrm{stat})\pm3~(\mathrm{sys})$ EeV, in the vicinity to the three
prominent features (ankle, instep, suppression) of the cosmic-ray flux. The
energy evolution of the mean and standard deviation of the measured
$X_\mathrm{max}$ distributions indicates that the mass composition becomes
increasingly heavier and purer, thus being incompatible with a large fraction
of light nuclei between 50 EeV and 100 EeV.
We report an investigation of the mass composition of cosmic rays with
energies from 3 to 100 EeV (1 EeV=$10^{18}$ eV) using the distributions of the
depth of shower maximum $X_\mathrm{max}$. The ...analysis relies on ${\sim}50,000$
events recorded by the Surface Detector of the Pierre Auger Observatory and a
deep-learning-based reconstruction algorithm. Above energies of 5 EeV, the data
set offers a 10-fold increase in statistics with respect to fluorescence
measurements at the Observatory. After cross-calibration using the Fluorescence
Detector, this enables the first measurement of the evolution of the mean and
the standard deviation of the $X_\mathrm{max}$ distributions up to 100 EeV. Our
findings are threefold:
(1.) The evolution of the mean logarithmic mass towards a heavier composition
with increasing energy can be confirmed and is extended to 100 EeV.
(2.) The evolution of the fluctuations of $X_\mathrm{max}$ towards a heavier
and purer composition with increasing energy can be confirmed with high
statistics. We report a rather heavy composition and small fluctuations in
$X_\mathrm{max}$ at the highest energies.
(3.) We find indications for a characteristic structure beyond a constant
change in the mean logarithmic mass, featuring three breaks that are observed
in proximity to the ankle, instep, and suppression features in the energy
spectrum.
