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$^2$ 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$_{max}$ 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

A search for point sources of EeV photons

Measurements of air showers made using the hybrid technique developed with the fluorescence and surface detectors of the Pierre Auger Observatory allow a sensitive search for point sources of EeV photons anywhere in the exposed sky. A multivariate analysis reduces the background of hadronic cosmic rays. The search is sensitive to a declination band from -85{\deg} to +20{\deg}, in an energy range from 10^17.3 eV to 10^18.5 eV. No photon point source has been detected. An upper limit on the photon flux has been derived for every direction. The mean value of the energy flux limit that results from this, assuming a photon spectral index of -2, is 0.06 eV cm^-2 s^-1, and no celestial direction exceeds 0.25 eV cm^-2 s^-1. These upper limits constrain scenarios in which EeV cosmic ray protons are emitted by non-transient sources in the Galaxy.Comment: 28 pages, 10 figures, accepted for publication in The Astrophysical Journa

The Pierre Auger Observatory III: Other Astrophysical Observations

Astrophysical observations of ultra-high-energy cosmic rays with the Pierre Auger ObservatoryComment: Contributions to the 32nd International Cosmic Ray Conference, Beijing, China, August 201

Dynamic recrystallization nanoarchitectonics of FeCrCuMnNi multi-phase high entropy alloy

Dynamic recrystallization behavior of the FeCrCuMnNi high entropy alloy (HEA) was investigated through hot compression test at different temperatures and at constant strain rate. The results revealed that during hot deformation of FeCrCuMnNi HEA, flow stress and work hardening rate rapidly decreased with increasing the deformation temperature. Discontinuous dynamic recrystallization (dDRX) was found to be the main active mechanism during hot deformation, which was the governing mechanism even at higher temperatures. In addition, bulging was an effective mechanism for inducing new recrystallized nuclei. Grain growth was occurred at slow strain rate in comparison to conventional alloys and other HEAs. This behavior was attributed to the continuous nucleation during dDRX, sluggish diffusion, high solution hardening characteristics of HEAs, and the presence of multiple phases in the FeCrCuMnNi HEA. Texture analysis showed that at lower temperatures, deformation texture including // CA fiber was formed. By increasing the deformation temperature, the formation of recrystallization texture fibers such as // CA and // CA rapidly intensified

Measurement of the cosmic ray spectrum above 4×10184{\times}10^{18} eV using inclined events detected with the Pierre Auger Observatory

A measurement of the cosmic-ray spectrum for energies exceeding $4{\times}10^{18}$ eV is presented, which is based on the analysis of showers with zenith angles greater than $60^{\circ}$ detected with the Pierre Auger Observatory between 1 January 2004 and 31 December 2013. The measured spectrum confirms a flux suppression at the highest energies. Above $5.3{\times}10^{18}$ eV, the "ankle", the flux can be described by a power law $E^{-\gamma}$ with index $\gamma=2.70 \pm 0.02 \,\text{(stat)} \pm 0.1\,\text{(sys)}$ followed by a smooth suppression region. For the energy ($E_\text{s}$) at which the spectral flux has fallen to one-half of its extrapolated value in the absence of suppression, we find $E_\text{s}=(5.12\pm0.25\,\text{(stat)}^{+1.0}_{-1.2}\,\text{(sys)}){\times}10^{19}$ eV.Comment: Replaced with published version. Added journal reference and DO

Reconstruction of inclined air showers detected with the Pierre Auger Observatory

We describe the method devised to reconstruct inclined cosmic-ray air showers with zenith angles greater than $60^\circ$ detected with the surface array of the Pierre Auger Observatory. The measured signals at the ground level are fitted to muon density distributions predicted with atmospheric cascade models to obtain the relative shower size as an overall normalization parameter. The method is evaluated using simulated showers to test its performance. The energy of the cosmic rays is calibrated using a sub-sample of events reconstructed with both the fluorescence and surface array techniques. The reconstruction method described here provides the basis of complementary analyses including an independent measurement of the energy spectrum of ultra-high energy cosmic rays using very inclined events collected by the Pierre Auger Observatory.Comment: 27 pages, 19 figures, accepted for publication in Journal of Cosmology and Astroparticle Physics (JCAP

The Pierre Auger Observatory: Contributions to the 34th International Cosmic Ray Conference (ICRC 2015)

Contributions of the Pierre Auger Collaboration to the 34th International Cosmic Ray Conference, 30 July - 6 August 2015, The Hague, The NetherlandsComment: 24 proceedings, the 34th International Cosmic Ray Conference, 30 July - 6 August 2015, The Hague, The Netherlands; will appear in PoS(ICRC2015

Reducibility of high-grade pellets directly reduced in hydrogen atmosphere: Modeling and experimental procedure

Abstract The paper analyzes the behavior of high-grade pellets specially developed for hydrogen direct reduction (HDRI). The reducibility of these pellets depends largely on their composition, porosity, pore structure and distribution. X-ray tomographic analyzes of the unreduced pellets showed different degrees of porosity as well as different pore sizes and distributions in each observed pellet. This prompted us to investigate the reduction behavior of each individual pellet at 1000 °C and 1 bar. The effect of composition on the reduction kinetics was analyzed using HSC software to isolate the effect of composition from the porosity structure of the pellets. After reduction, X-ray tomographic observations enabled the measurement of porosity variation in each pellet studied. The porosity variation data was used to validate a finite element model developed to analyze porosity evolution using COMSOL Multiphysics. The study found that larger pores have higher activity and a tendency to coalesce, forming interconnected networks that allow for better gas and heat diffusion. The results showed that porosity increased from approximately 30 % to approximately 65 % after reduction, and the close agreement between the experimental data and the FEM simulations confirmed the accuracy of the model. It was found that the presence of CaO and MgO increased the porosity and thus improved the reducibility, while the inhibitory effects of SiO2 and Al2O3 were minimized. These results contribute significantly to the optimization of pellet composition and structure for efficient and uniform reduction of iron oxides in hydrogen atmospheres.Abstract The paper analyzes the behavior of high-grade pellets specially developed for hydrogen direct reduction (HDRI). The reducibility of these pellets depends largely on their composition, porosity, pore structure and distribution. X-ray tomographic analyzes of the unreduced pellets showed different degrees of porosity as well as different pore sizes and distributions in each observed pellet. This prompted us to investigate the reduction behavior of each individual pellet at 1000 °C and 1 bar. The effect of composition on the reduction kinetics was analyzed using HSC software to isolate the effect of composition from the porosity structure of the pellets. After reduction, X-ray tomographic observations enabled the measurement of porosity variation in each pellet studied. The porosity variation data was used to validate a finite element model developed to analyze porosity evolution using COMSOL Multiphysics. The study found that larger pores have higher activity and a tendency to coalesce, forming interconnected networks that allow for better gas and heat diffusion. The results showed that porosity increased from approximately 30 % to approximately 65 % after reduction, and the close agreement between the experimental data and the FEM simulations confirmed the accuracy of the model. It was found that the presence of CaO and MgO increased the porosity and thus improved the reducibility, while the inhibitory effects of SiO2 and Al2O3 were minimized. These results contribute significantly to the optimization of pellet composition and structure for efficient and uniform reduction of iron oxides in hydrogen atmospheres

Energy Estimation of Cosmic Rays with the Engineering Radio Array of the Pierre Auger Observatory

The Auger Engineering Radio Array (AERA) is part of the Pierre Auger Observatory and is used to detect the radio emission of cosmic-ray air showers. These observations are compared to the data of the surface detector stations of the Observatory, which provide well-calibrated information on the cosmic-ray energies and arrival directions. The response of the radio stations in the 30 to 80 MHz regime has been thoroughly calibrated to enable the reconstruction of the incoming electric field. For the latter, the energy deposit per area is determined from the radio pulses at each observer position and is interpolated using a two-dimensional function that takes into account signal asymmetries due to interference between the geomagnetic and charge-excess emission components. The spatial integral over the signal distribution gives a direct measurement of the energy transferred from the primary cosmic ray into radio emission in the AERA frequency range. We measure 15.8 MeV of radiation energy for a 1 EeV air shower arriving perpendicularly to the geomagnetic field. This radiation energy -- corrected for geometrical effects -- is used as a cosmic-ray energy estimator. Performing an absolute energy calibration against the surface-detector information, we observe that this radio-energy estimator scales quadratically with the cosmic-ray energy as expected for coherent emission. We find an energy resolution of the radio reconstruction of 22% for the data set and 17% for a high-quality subset containing only events with at least five radio stations with signal.Comment: Replaced with published version. Added journal reference and DO