The energy spectrum of cosmic rays beyond the turn-down around 10^17 eV as measured with the surface detector of the Pierre Auger Observatory

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 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

Reconstruction of events recorded with the surface detector of the Pierre Auger Observatory

Cosmic rays arriving at Earth collide with the upper parts of the atmosphere, thereby inducing extensive air showers. When secondary particles from the cascade arrive at the ground, they are measured by surface detector arrays. We describe the methods applied to the measurements of the surface detector of the Pierre Auger Observatory to reconstruct events with zenith angles less than 60o using the timing and signal information recorded using the water-Cherenkov detector stations. In addition, we assess the accuracy of these methods in reconstructing the arrival directions of the primary cosmic ray particles and the sizes of the induced showers

An Indication of Anisotropy in Arrival Directions of Ultra-high-energy Cosmic Rays through Comparison to the Flux Pattern of Extragalactic Gamma-Ray Sources

A new analysis of the data set from the Pierre Auger Observatory provides evidence for anisotropy in the arrival directions of ultra-high-energy cosmic rays on an intermediate angular scale, which is indicative of excess arrivals from strong, nearby sources. The data consist of 5514 events above 20 EeV with zenith angles up to 80 degrees. recorded before 2017 April 30. Sky models have been created for two distinct populations of extragalactic gamma-ray emitters: active galactic nuclei from the second catalog of hard Fermi-LAT sources (2FHL) and starburst galaxies from a sample that was examined with Fermi-LAT. Flux-limited samples, which include all types of galaxies from the Swift-BAT and 2MASS surveys, have been investigated for comparison. The sky model of cosmic-ray density constructed using each catalog has two free parameters, the fraction of events correlating with astrophysical objects, and an angular scale characterizing the clustering of cosmic rays around extragalactic sources. A maximum-likelihood ratio test is used to evaluate the best values of these parameters and to quantify the strength of each model by contrast with isotropy. It is found that the starburst model fits the data better than the hypothesis of isotropy with a statistical significance of 4.0 sigma, the highest value of the test statistic being for energies above 39 EeV. The three alternative models are favored against isotropy with 2.7 sigma-3.2 sigma significance. The origin of the indicated deviation from isotropy is examined and prospects for more sensitive future studies are discussed

Inferences on mass composition and tests of hadronic interactions from 0.3 to 100 EeV using the water-Cherenkov detectors of the Pierre Auger Observatory

We present a new method for probing the hadronic interaction models at ultrahigh energy and extracting details about mass composition. This is done using the time profiles of the signals recorded with the water-Cherenkov detectors of the Pierre Auger Observatory. The profiles arise from a mix of the muon and electromagnetic components of air showers. Using the risetimes of the recorded signals, we define a new parameter, which we use to compare our observations with predictions from simulations. We find, first, inconsistencies between our data and predictions over a greater energy range and with substantially more events than in previous studies. Second, by calibrating the new parameter with fluorescence measurements from observations made at the Auger Observatory, we can infer the depth of shower maximum Xmax for a sample of over 81,000 events extending from 0.3 to over 100 EeV. Above 30 EeV, the sample is nearly 14 times larger than what is currently available from fluorescence measurements and extending the covered energy range by half a decade. The energy dependence of ?Xmaxcopyright is compared to simulations and interpreted in terms of the mean of the logarithmic mass. We find good agreement with previous work and extend the measurement of the mean depth of shower maximum to greater energies than before, reducing significantly the statistical uncertainty associated with the inferences about mass composition

The FRAM robotic telescope for atmospheric monitoring at the Pierre Auger Observatory

FRAM (F/Photometric Robotic Atmospheric Monitor) is a robotic telescope operated at the Pierre Auger Observatory in Argentina for the purposes of atmospheric monitoring using stellar photometry. As a passive system which does not produce any light that could interfere with the observations of the fluorescence telescopes of the observatory, it complements the active monitoring systems that use lasers. We discuss the applications of stellar photometry for atmospheric monitoring at optical observatories in general and the particular modes of operation employed by the Auger FRAM. We describe in detail the technical aspects of FRAM, the hardware and software requirements for a successful operation of a robotic telescope for such a purpose and their implementation within the FRAM system

Search for photons with energies above 1018eV using the hybrid detector of the Pierre Auger Observatory

A search for ultra-high energy photons with energies above 1EeV is performed using nine years of data collected by the Pierre Auger Observatory in hybrid operation mode. An unprecedented separation power between photon and hadron primaries is achieved by combining measurements of the longitudinal air-shower development with the particle content at ground measured by the fluorescence and surface detectors, respectively. Only three photon candidates at energies 1\u20132EeV are found, which is compatible with the expected hadron induced background. Upper limits on the integral flux of ultra-high energy photons of 0.027, 0.009, 0.008, 0.008 and 0.007 km 122 sr 121 yr 121 are derived at 95% C.L. for energy thresholds of 1, 2, 3, 5 and 10EeV. These limits bound the fractions of photons in the all-particle integral flux below 0.1%, 0.15%, 0.33%, 0.85% and 2.7%. For the first time the photon fraction at EeV energies is constrained at the sub-percent level. The improved limits are below the flux of diffuse photons predicted by some astrophysical scenarios for cosmogenic photon production. The new results rule-out the early top-down models 12 in which ultra-high energy cosmic rays are produced by, e.g., the decay of super-massive particles 12 and challenge the most recent super-heavy dark matter model

Design, upgrade and characterization of the silicon photomultiplier front-end for the AMIGA detector at the Pierre Auger Observatory

none359AMIGA (Auger Muons and Infill for the Ground Array) is an upgrade of the Pierre Auger Observatory to complement the study of ultra-high-energy cosmic rays (UHECR) by measuring the muon content of extensive air showers (EAS). It consists of an array of 61 water Cherenkov detectors on a denser spacing in combination with underground scintillation detectors used for muon density measurement. Each detector is composed of three scintillation modules, with 10 m(2) detection area per module, buried at 2.3 m depth, resulting in a total detection area of 30 m(2). Silicon photomultiplier sensors (SiPM) measure the amount of scintillation light generated by charged particles traversing the modules. In this paper, the design of the front-end electronics to process the signals of those SiPMs and test results from the laboratory and from the Pierre Auger Observatory are described. Compared to our previous prototype, the new electronics shows a higher performance, higher efficiency and lower power consumption, and it has a new acquisition system with increased dynamic range that allows measurements closer to the shower core. The new acquisition system is based on the measurement of the total charge signal that the muonic component of the cosmic ray shower generates in the detector.noneAab A.; Abreu P.; Aglietta M.; Albury J.M.; Allekotte I.; Almela A.; Alvarez-Muniz J.; Alves Batista R.; Anastasi G.A.; Anchordoqui L.; Andrada B.; Andringa S.; Aramo C.; Araujo Ferreira P.R.; Asorey H.; Assis P.; Avila G.; Badescu A.M.; Bakalova A.; Balaceanu A.; Barbato F.; Barreira Luz R.J.; Becker K.H.; Bellido J.A.; Berat C.; Bertaina M.E.; Bertou X.; Biermann P.L.; Bister T.; Biteau J.; Blazek J.; Bleve C.; Bohacova M.; Boncioli D.; Bonifazi C.; Bonneau Arbeletche L.; Borodai N.; Botti A.M.; Brack J.; Bretz T.; Briechle F.L.; Buchholz P.; Bueno A.; Buitink S.; Buscemi M.; Caballero-Mora K.S.; Caccianiga L.; Canfora F.; Caracas I.; Carceller J.M.; Caruso R.; Castellina A.; Catalani F.; Cataldi G.; Cazon L.; Cerda M.; Chinellato J.A.; Choi K.; Chudoba J.; Chytka L.; Clay R.W.; Cobos Cerutti A.C.; Colalillo R.; Coleman A.; Coluccia M.R.; Conceicao R.; Condorelli A.; Consolati G.; Contreras F.; Convenga F.; Covault C.E.; Dasso S.; Daumiller K.; Dawson B.R.; Day J.A.; de Almeida R.M.; de Jesus J.; de Jong S.J.; de Mauro G.; de Mello Neto J.R.T.; de Mitri I.; de Oliveira J.; de Oliveira Franco D.; de Souza V.; de Vito E.; Debatin J.; del Rio M.; Deligny O.; Di Matteo A.; Dobrigkeit C.; D'Olivo J.C.; dos Anjos R.C.; Dova M.T.; Ebr J.; Engel R.; Epicoco I.; Erdmann M.; Escobar C.O.; Etchegoyen A.; Falcke H.; Farmer J.; Farrar G.; Fauth A.C.; Fazzini N.; Feldbusch F.; Fenu F.; Fick B.; Figueira J.M.; Filipcic A.; Fodran T.; Freire M.M.; Fujii T.; Fuster A.; Galea C.; Galelli C.; Garcia B.; Garcia Vegas A.L.; Gemmeke H.; Gesualdi F.; Gherghel-Lascu A.; Ghia P.L.; Giaccari U.; Giammarchi M.; Giller M.; Glombitza J.; Gobbi F.; Gollan F.; Golup G.; Gomez Berisso M.; Gomez Vitale P.F.; Gongora J.P.; Gonzalez J.M.; Gonzalez N.; Goos I.; Gora D.; Gorgi A.; Gottowik M.; Grubb T.D.; Guarino F.; Guedes G.P.; Guido E.; Hahn S.; Hampel M.R.; Hansen P.; Harari D.; Harvey V.M.; Haungs A.; Hebbeker T.; Heck D.; Hill G.C.; Hojvat C.; Horandel J.R.; Horvath P.; Hrabovsky M.; Huege T.; Hulsman J.; Insolia A.; Isar P.G.; Johnsen J.A.; Jurysek J.; Kaapa A.; Kampert K.H.; Keilhauer B.; Kemp J.; Klages H.O.; Kleifges M.; Kleinfeller J.; Kopke M.; Lago B.L.; Lang R.G.; Langner N.; Leigui de Oliveira M.A.; Lenok V.; Letessier-Selvon A.; Lhenry-Yvon I.; Lo Presti D.; Lopes L.; Lopez R.; Luce Q.; Lucero A.; Lundquist J.P.; Machado Payeras A.; Mancarella G.; Mandat D.; Manning B.C.; Manshanden J.; Mantsch P.; Marafico S.; Mariazzi A.G.; Maris I.C.; Marsella G.; Martello D.; Martinez H.; Martinez Bravo O.; Mastrodicasa M.; Mathes H.J.; Matthews J.; Matthiae G.; Mayotte E.; Mazur P.O.; Medina-Tanco G.; Melo D.; Menshikov A.; Merenda K.-D.; Michal S.; Micheletti M.I.; Miramonti L.; Mollerach S.; Montanet F.; Morello C.; Mostafa M.; Muller A.L.; Muller M.A.; Mulrey K.; Mussa R.; Muzio M.; Namasaka W.M.; Nellen L.; Niculescu-Oglinzanu M.; Niechciol M.; Nitz D.; Nosek D.; Novotny V.; Nozka L.; Nucita A.; Nunez L.A.; Palatka M.; Pallotta J.; Papenbreer P.; Parente G.; Parra A.; Pech M.; Pedreira F.; Pekala J.; Pelayo R.; Pena-Rodriguez J.; Perez Armand J.; Perlin M.; Perrone L.; Petrera S.; Pierog T.; Pimenta M.; Pirronello V.; Platino M.; Pont B.; Pothast M.; Privitera P.; Prouza M.; Puyleart A.; Querchfeld S.; Rautenberg J.; Ravignani D.; Reininghaus M.; Ridky J.; Riehn F.; Risse M.; Ristori P.; Rizi V.; Rodrigues de Carvalho W.; Rodriguez Rojo J.; Roncoroni M.J.; Roth M.; Roulet E.; Rovero A.C.; Ruehl P.; Saffi S.J.; Saftoiu A.; Salamida F.; Salazar H.; Salina G.; Sanabria Gomez J.D.; Sanchez F.; Santos E.M.; Santos E.; Sarazin F.; Sarmento R.; Sarmiento-Cano C.; Sato R.; Savina P.; Schafer C.M.; Scherini V.; Schieler H.; Schimassek M.; Schimp M.; Schluter F.; Schmidt D.; Scholten O.; Schovanek P.; Schroder F.G.; Schroder S.; Schulte J.; Sciutto S.J.; Scornavacche M.; Shellard R.C.; Sigl G.; Silli G.; Sima O.; Smida R.; Sommers P.; Soriano J.F.; Souchard J.; Squartini R.; Stadelmaier M.; Stanca D.; Stanic S.; Stasielak J.; Stassi P.; Streich A.; Suarez-Duran M.; Sudholz T.; Suomijarvi T.; Supanitsky A.D.; Supik J.; Szadkowski Z.; Taboada A.; Tapia A.; Timmermans C.; Tkachenko O.; Tobiska P.; Todero Peixoto C.J.; Tome B.; Travaini A.; Travnicek P.; Trimarelli C.; Trini M.; Tueros M.; Ulrich R.; Unger M.; Vaclavek L.; Vacula M.; Valdes Galicia J.F.; Valore L.; Varela E.; Varma V.K.C.; Vasquez-Ramirez A.; Veberic D.; Ventura C.; Vergara Quispe I.D.; Verzi V.; Vicha J.; Vink J.; Vorobiov S.; Wahlberg H.; Watson A.A.; Weber M.; Weindl A.; Wiencke L.; Wilczynski H.; Winchen T.; Wirtz M.; Wittkowski D.; Wundheiler B.; Yushkov A.; Zapparrata O.; Zas E.; Zavrtanik D.; Zavrtanik M.; Zehrer L.; Zepeda A.Aab, A.; Abreu, P.; Aglietta, M.; Albury, J. M.; Allekotte, I.; Almela, A.; Alvarez-Muniz, J.; Alves Batista, R.; Anastasi, G. A.; Anchordoqui, L.; Andrada, B.; Andringa, S.; Aramo, C.; Araujo Ferreira, P. R.; Asorey, H.; Assis, P.; Avila, G.; Badescu, A. M.; Bakalova, A.; Balaceanu, A.; Barbato, F.; Barreira Luz, R. J.; Becker, K. H.; Bellido, J. A.; Berat, C.; Bertaina, M. E.; Bertou, X.; Biermann, P. L.; Bister, T.; Biteau, J.; Blazek, J.; Bleve, C.; Bohacova, M.; Boncioli, D.; Bonifazi, C.; Bonneau Arbeletche, L.; Borodai, N.; Botti, A. M.; Brack, J.; Bretz, T.; Briechle, F. L.; Buchholz, P.; Bueno, A.; Buitink, S.; Buscemi, M.; Caballero-Mora, K. S.; Caccianiga, L.; Canfora, F.; Caracas, I.; Carceller, J. M.; Caruso, R.; Castellina, A.; Catalani, F.; Cataldi, G.; Cazon, L.; Cerda, M.; Chinellato, J. A.; Choi, K.; Chudoba, J.; Chytka, L.; Clay, R. W.; Cobos Cerutti, A. C.; Colalillo, R.; Coleman, A.; Coluccia, M. R.; Conceicao, R.; Condorelli, A.; Consolati, G.; Contreras, F.; Convenga, F.; Covault, C. E.; Dasso, S.; Daumiller, K.; Dawson, B. R.; Day, J. A.; de Almeida, R. M.; de Jesus, J.; de Jong, S. J.; de Mauro, G.; de Mello Neto, J. R. T.; de Mitri, I.; de Oliveira, J.; de Oliveira Franco, D.; de Souza, V.; de Vito, E.; Debatin, J.; del Rio, M.; Deligny, O.; Di Matteo, A.; Dobrigkeit, C.; D'Olivo, J. C.; dos Anjos, R. C.; Dova, M. T.; Ebr, J.; Engel, R.; Epicoco, I.; Erdmann, M.; Escobar, C. O.; Etchegoyen, A.; Falcke, H.; Farmer, J.; Farrar, G.; Fauth, A. C.; Fazzini, N.; Feldbusch, F.; Fenu, F.; Fick, B.; Figueira, J. M.; Filipcic, A.; Fodran, T.; Freire, M. M.; Fujii, T.; Fuster, A.; Galea, C.; Galelli, C.; Garcia, B.; Garcia Vegas, A. L.; Gemmeke, H.; Gesualdi, F.; Gherghel-Lascu, A.; Ghia, P. L.; Giaccari, U.; Giammarchi, M.; Giller, M.; Glombitza, J.; Gobbi, F.; Gollan, F.; Golup, G.; Gomez Berisso, M.; Gomez Vitale, P. F.; Gongora, J. P.; Gonzalez, J. M.; Gonzalez, N.; Goos, I.; Gora, D.; Gorgi, A.; Gottowik, M.; Grubb, T. D.; Guarino, F.; Guedes, G. P.; Guido, E.; Hahn, S.; Hampel, M. R.; Hansen, P.; Harari, D.; Harvey, V. M.; Haungs, A.; Hebbeker, T.; Heck, D.; Hill, G. C.; Hojvat, C.; Horandel, J. R.; Horvath, P.; Hrabovsky, M.; Huege, T.; Hulsman, J.; Insolia, A.; Isar, P. G.; Johnsen, J. A.; Jurysek, J.; Kaapa, A.; Kampert, K. H.; Keilhauer, B.; Kemp, J.; Klages, H. O.; Kleifges, M.; Kleinfeller, J.; Kopke, M.; Lago, B. L.; Lang, R. G.; Langner, N.; Leigui de Oliveira, M. A.; Lenok, V.; Letessier-Selvon, A.; Lhenry-Yvon, I.; Lo Presti, D.; Lopes, L.; Lopez, R.; Luce, Q.; Lucero, A.; Lundquist, J. P.; Machado Payeras, A.; Mancarella, G.; Mandat, D.; Manning, B. C.; Manshanden, J.; Mantsch, P.; Marafico, S.; Mariazzi, A. G.; Maris, I. C.; Marsella, G.; Martello, D.; Martinez, H.; Martinez Bravo, O.; Mastrodicasa, M.; Mathes, H. J.; Matthews, J.; Matthiae, G.; Mayotte, E.; Mazur, P. O.; Medina-Tanco, G.; Melo, D.; Menshikov, A.; Merenda, K. -D.; Michal, S.; Micheletti, M. I.; Miramonti, L.; Mollerach, S.; Montanet, F.; Morello, C.; Mostafa, M.; Muller, A. L.; Muller, M. A.; Mulrey, K.; Mussa, R.; Muzio, M.; Namasaka, W. M.; Nellen, L.; Niculescu-Oglinzanu, M.; Niechciol, M.; Nitz, D.; Nosek, D.; Novotny, V.; Nozka, L.; Nucita, A.; Nunez, L. A.; Palatka, M.; Pallotta, J.; Papenbreer, P.; Parente, G.; Parra, A.; Pech, M.; Pedreira, F.; Pekala, J.; Pelayo, R.; Pena-Rodriguez, J.; Perez Armand, J.; Perlin, M.; Perrone, L.; Petrera, S.; Pierog, T.; Pimenta, M.; Pirronello, V.; Platino, M.; Pont, B.; Pothast, M.; Privitera, P.; Prouza, M.; Puyleart, A.; Querchfeld, S.; Rautenberg, J.; Ravignani, D.; Reininghaus, M.; Ridky, J.; Riehn, F.; Risse, M.; Ristori, P.; Rizi, V.; Rodrigues de Carvalho, W.; Rodriguez Rojo, J.; Roncoroni, M. J.; Roth, M.; Roulet, E.; Rovero, A. C.; Ruehl, P.; Saffi, S. J.; Saftoiu, A.; Salamida, F.; Salazar, H.; Salina, G.; Sanabria Gomez, J. D.; Sanchez, F.; Santos, E. M.; Santos, E.; Sarazin, F.; Sarmento, R.; Sarmiento-Cano, C.; Sato, R.; Savina, P.; Schafer, C. M.; Scherini, V.; Schieler, H.; Schimassek, M.; Schimp, M.; Schluter, F.; Schmidt, D.; Scholten, O.; Schovanek, P.; Schroder, F. G.; Schroder, S.; Schulte, J.; Sciutto, S. J.; Scornavacche, M.; Shellard, R. C.; Sigl, G.; Silli, G.; Sima, O.; Smida, R.; Sommers, P.; Soriano, J. F.; Souchard, J.; Squartini, R.; Stadelmaier, M.; Stanca, D.; Stanic, S.; Stasielak, J.; Stassi, P.; Streich, A.; Suarez-Duran, M.; Sudholz, T.; Suomijarvi, T.; Supanitsky, A. D.; Supik, J.; Szadkowski, Z.; Taboada, A.; Tapia, A.; Timmermans, C.; Tkachenko, O.; Tobiska, P.; Todero Peixoto, C. J.; Tome, B.; Travaini, A.; Travnicek, P.; Trimarelli, C.; Trini, M.; Tueros, M.; Ulrich, R.; Unger, M.; Vaclavek, L.; Vacula, M.; Valdes Galicia, J. F.; Valore, L.; Varela, E.; Varma, V. K. C.; Vasquez-Ramirez, A.; Veberic, D.; Ventura, C.; Vergara Quispe, I. D.; Verzi, V.; Vicha, J.; Vink, J.; Vorobiov, S.; Wahlberg, H.; Watson, A. A.; Weber, M.; Weindl, A.; Wiencke, L.; Wilczynski, H.; Winchen, T.; Wirtz, M.; Wittkowski, D.; Wundheiler, B.; Yushkov, A.; Zapparrata, O.; Zas, E.; Zavrtanik, D.; Zavrtanik, M.; Zehrer, L.; Zepeda, A

Combined fit of spectrum and composition data as measured by the Pierre Auger Observatory

We present a combined fit of a simple astrophysical model of UHECR sources to both the energy spectrum and mass composition data measured by the Pierre Auger Observatory. The fit has been performed for energies above 5 c5 1018 eV, i.e. the region of the all-particle spectrum above the so-called "ankle" feature. The astrophysical model we adopted consists of identical sources uniformly distributed in a comoving volume, where nuclei are accelerated through a rigidity-dependent mechanism. The fit results suggest sources characterized by relatively low maximum injection energies, hard spectra and heavy chemical composition. We also show that uncertainties about physical quantities relevant to UHECR propagation and shower development have a non-negligible impact on the fit results