Phys. Rev. Lett. 125, 121106 (2020) We report a measurement of the energy spectrum of cosmic rays above
$2.5{\times} 10^{18}$ eV based on $215,030$ events. New results are presented:
at about ...$1.3{\times} 10^{19}$ eV, the spectral index changes from $2.51 \pm
0.03 \textrm{ (stat.)} \pm 0.05 \textrm{ (sys.)}$ to $3.05 \pm 0.05 \textrm{
(stat.)}\pm 0.10\textrm{ (sys.)}$, evolving to $5.1\pm0.3\textrm{ (stat.)} \pm
0.1\textrm{ (sys.)}$ beyond $5{\times} 10^{19}$ eV, while no significant
dependence of spectral features on the declination is seen in the accessible
range. These features of the spectrum can be reproduced in models with
energy-dependent mass composition. The energy density in cosmic rays above
$5{\times} 10^{18}$ eV is $(5.66 \pm 0.03 \textrm{ (stat.)} \pm 1.40 \textrm{
(sys.)} ) {\times} 10^{53}~$erg Mpc$^{-3}$.
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.
We present a measurement of the cosmic-ray spectrum above 100\,PeV using the part of the surface detector of the Pierre Auger Observatory that has a spacing of 750~m. An inflection of the spectrum is ...observed, confirming the presence of the so-called \emph{second-knee} feature. The spectrum is then combined with that of the 1500\,m array to produce a single measurement of the flux, linking this spectral feature with the three additional breaks at the highest energies. The combined spectrum, with an energy scale set calorimetrically via fluorescence telescopes and using a single detector type, results in the most statistically and systematically precise measurement of spectral breaks yet obtained. These measurements are critical for furthering our understanding of the highest energy cosmic rays.
Ultra-high-energy photons with energies exceeding \(10^{17}\) 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 \(10^{15}\) eV range further motivate searches for even higher-energy photons. In this paper, we present a search for photons with energies exceeding \(2{\times}10^{17}\) eV using about 5.5 years 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 \(10^{17}\) and \(10^{18}\) eV.
The atmospheric depth of the air shower maximum \(X_{\mathrm{max}}\) is an observable commonly used for the determination of the nuclear mass composition of ultra-high energy cosmic rays. Direct ...measurements of \(X_{\mathrm{max}}\) are performed using observations of the longitudinal shower development with fluorescence telescopes. At the same time, several methods have been proposed for an indirect estimation of \(X_{\mathrm{max}}\) from the characteristics of the shower particles registered with surface detector arrays. In this paper, we present a deep neural network (DNN) for the estimation of \(X_{\mathrm{max}}\). The reconstruction relies on the signals induced by shower particles in the ground based water-Cherenkov detectors of the Pierre Auger Observatory. The network architecture features recurrent long short-term memory layers to process the temporal structure of signals and hexagonal convolutions to exploit the symmetry of the surface detector array. We evaluate the performance of the network using air showers simulated with three different hadronic interaction models. Thereafter, we account for long-term detector effects and calibrate the reconstructed \(X_{\mathrm{max}}\) using fluorescence measurements. Finally, we show that the event-by-event resolution in the reconstruction of the shower maximum improves with increasing shower energy and reaches less than \(25~\mathrm{g/cm^{2}}\) at energies above \(2\times 10^{19}~\mathrm{eV}\).
We report a measurement of the energy spectrum of cosmic rays for energies above \(2.5 {\times} 10^{18}~\)eV based on 215,030 events recorded with zenith angles below \(60^\circ\). A key feature of ...the work is that the estimates of the energies are independent of assumptions about the unknown hadronic physics or of the primary mass composition. The measurement is the most precise made hitherto with the accumulated exposure being so large that the measurements of the flux are dominated by systematic uncertainties except at energies above \(5 {\times} 10^{19}~\)eV. The principal conclusions are: (1) The flattening of the spectrum near \(5 {\times} 10^{18}~\)eV, the so-called "ankle", is confirmed. (2) The steepening of the spectrum at around \(5 {\times} 10^{19}~\)eV is confirmed. (3) A new feature has been identified in the spectrum: in the region above the ankle the spectral index \(\gamma\) of the particle flux (\(\propto E^{-\gamma}\)) changes from \(2.51 \pm 0.03~{\rm (stat.)} \pm 0.05~{\rm (sys.)}\) to \(3.05 \pm 0.05~{\rm (stat.)} \pm 0.10~{\rm (sys.)}\) before changing sharply to \(5.1 \pm 0.3~{\rm (stat.)} \pm 0.1~{\rm (sys.)}\) above \(5 {\times} 10^{19}~\)eV. (4) No evidence for any dependence of the spectrum on declination has been found other than a mild excess from the Southern Hemisphere that is consistent with the anisotropy observed above \(8 {\times} 10^{18}~\)eV.
We report a measurement of the energy spectrum of cosmic rays above \(2.5{\times} 10^{18}\) eV based on \(215,030\) events. New results are presented: at about \(1.3{\times} 10^{19}\) eV, the ...spectral index changes from \(2.51 \pm 0.03 \textrm{ (stat.)} \pm 0.05 \textrm{ (sys.)}\) to \(3.05 \pm 0.05 \textrm{ (stat.)}\pm 0.10\textrm{ (sys.)}\), evolving to \(5.1\pm0.3\textrm{ (stat.)} \pm 0.1\textrm{ (sys.)}\) beyond \(5{\times} 10^{19}\) eV, while no significant dependence of spectral features on the declination is seen in the accessible range. These features of the spectrum can be reproduced in models with energy-dependent mass composition. The energy density in cosmic rays above \(5{\times} 10^{18}\) eV is \((5.66 \pm 0.03 \textrm{ (stat.)} \pm 1.40 \textrm{ (sys.)} ) {\times} 10^{53}~\)erg Mpc\(^{-3}\).
We have conducted a multiwavelength survey of 42 radio loud narrow-1ine Seyfert 1 galaxies (RLNLS1s), selected by searching among all the known sources of this type and omitting those with steep ...radio spectra. We analyse data from radio frequencies to X-rays, and supplement these with information available from online catalogues and the literature in order to cover the full electromagnetic spectrum. This is the largest known multiwavelength survey for this type of source. We detected 90% of the sources in X-rays and found 17% at γ rays. Extreme variability at high energies was also found, down to timescales as short as hours. In some sources, dramatic spectral and flux changes suggest interplay between a relativistic jet and the accretion disk. The estimated masses of the central black holes are in the range ~106−8 M⊙, lower than those of blazars, while the accretion luminosities span a range from ~0.01 to ~0.49 times the Eddington limit, with an outlier at 0.003, similar to those of quasars. The distribution of the calculated jet power spans a range from ~1042.6 to ~1045.6 erg s-1, generally lower than quasars and BL Lac objects, but partially overlapping with the latter. Once normalised by the mass of the central black holes, the jet power of the three types of active galactic nuclei are consistent with each other, indicating that the jets are similar and the observational differences are due to scaling factors. Despite the observational differences, the central engine of RLNLS1s is apparently quite similar to that of blazars. The historical difficulties in finding radio-loud narrow-line Seyfert 1 galaxies might be due to their low power and to intermittent jetactivity.
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