Browsing by Author "Espadanal, Joao"
Now showing 1 - 10 of 29
Results Per Page
Sort Options
- A search for point sources of EeV photonsPublication . Pierre Auger collaboration (484 authors); Abreu, Pedro; Andringa, Sofia; Assis, Pedro; Brogueira, Pedro; Cazon, Lorenzo; Conceição, Ruben; Diogo, Francisco; Espadanal, Joao; Gonçalves, Patrícia; Oliveira, Micael; Pimenta, Mário; Santo, Catarina E; Santos, Eva; Sarmento, Raul; Tomé, BernardoMeasurements 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° to +20°, 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.
- A Targeted Search for Point Sources of EeV NeutronsPublication . Pierre Auger collaboration (496 authors); Abreu, Pedro; Andringa, Sofia; Assis, Pedro; Brogueira, Pedro; Cazon, Lorenzo; Conceição, Ruben; Diogo, Francisco; Espadanal, Joao; Gonçalves, Patrícia; Oliveira, Micael; Pimenta, Mário; Santo, Catarina E; Santos, Eva; Sarmento, Raul; Tomé, BernardoA flux of neutrons from an astrophysical source in the Galaxy can be detected in the Pierre Auger Observatory as an excess of cosmic-ray air showers arriving from the direction of the source. To avoid the statistical penalty for making many trials, classes of objects are tested in combinations as nine 'target sets,' in addition to the search for a neutron flux from the Galactic center or from the Galactic plane. Within a target set, each candidate source is weighted in proportion to its electromagnetic flux, its exposure to the Auger Observatory, and its flux attenuation factor due to neutron decay. These searches do not find evidence for a neutron flux from any class of candidate sources. Tabulated results give the combined p-value for each class, with and without the weights, and also the flux upper limit for the most significant candidate source within each class. These limits on fluxes of neutrons significantly constrain models of EeV proton emission from non-transient discrete sources in the Galaxy.
- Antennas for the Detection of Radio Emission Pulses from Cosmic-RayPublication . Pierre Auger collaboration (515 authors); Abreu, Pedro; Andringa, Sofia; Assis, Pedro; Brogueira, Pedro; Cazon, Lorenzo; Conceição, Ruben; Diogo, Francisco; Espadanal, Joao; Gonçalves, Patrícia; Pimenta, Mário; Santo, Catarina E; Santos, Eva; Tomé, BernardoThe Pierre Auger Observatory is exploring the potential of the radio detection technique to study extensive air showers induced by ultra-high energy cosmic rays. The Auger Engineering Radio Array (AERA) addresses both technological and scientific aspects of the radio technique. A first phase of AERA has been operating since September 2010 with detector stations observing radio signals at frequencies between 30 and 80 MHz. In this paper we present comparative studies to identify and optimize the antenna design for the final configuration of AERA consisting of 160 individual radio detector stations. The transient nature of the air shower signal requires a detailed description of the antenna sensor. As the ultra-wideband reception of pulses is not widely discussed in antenna literature, we review the relevant antenna characteristics and enhance theoretical considerations towards the impulse response of antennas including polarization effects and multiple signal reflections. On the basis of the vector effective length we study the transient response characteristics of three candidate antennas in the time domain. Observing the variation of the continuous galactic background intensity we rank the antennas with respect to the noise level added to the galactic signal.
- Azimuthal Asymmetry in the Risetime of the Surface Detector Signals of the Pierre Auger ObservatoryPublication . Pierre Auger collaboration (434 authors); Abreu, Pedro; Andringa, Sofia; Assis, Pedro; Blanco, Alberto; Cazon, Lorenzo; Conceição, Ruben; Diogo, Francisco; Espadanal, Joao; Lopes, Luis; Pimenta, Mário; Santos, Eva; Sarmento, Raul; Tomé, BernardoThe azimuthal asymmetry in the risetime of signals in Auger surface detector stations is a source of information on shower development. The azimuthal asymmetry is due to a combination of the longitudinal evolution of the shower and geometrical effects related to the angles of incidence of the particles into the detectors. The magnitude of the effect depends upon the zenith angle and state of development of the shower and thus provides a novel observable, (secθ)max, sensitive to the mass composition of cosmic rays above 3×1018 eV. By comparing measurements with predictions from shower simulations, we find for both of our adopted models of hadronic physics (QGSJETII-04 and EPOS-LHC) an indication that the mean cosmic-ray mass increases slowly with energy, as has been inferred from other studies. However, the mass estimates are dependent on the shower model and on the range of distance from the shower core selected. Thus the method has uncovered further deficiencies in our understanding of shower modeling that must be resolved before the mass composition can be inferred from (secθ)max.
- Bounds on the density of sources of ultra-high energy cosmic rays from the Pierre Auger ObservatoryPublication . Pierre Auger collaboration (512 authors); Abreu, Pedro; Andringa, Sofia; Assis, Pedro; Brogueira, Pedro; Cazon, Lorenzo; Conceição, Ruben; Diogo, Francisco; Espadanal, Joao; Gonçalves, Patrícia; Oliveira, Micael; Pimenta, Mário; Santo, Catarina E; Santos, Eva; Tomé, BernardoWe derive lower bounds on the density of sources of ultra-high energy cosmic rays from the lack of significant clustering in the arrival directions of the highest energy events detected at the Pierre Auger Observatory. The density of uniformly distributed sources of equal intrinsic intensity was found to be larger than ~ (0.06−5) × 10(−)(4) Mpc(−)(3) at 95% CL, depending on the magnitude of the magnetic deflections. Similar bounds, in the range (0.2−7) × 10(−)(4) Mpc(−)(3), were obtained for sources following the local matter distribution.
- Depth of maximum of air-shower profiles at the Pierre Auger Observatory. I. Measurements at energies above $10^{17.8}$ eVPublication . Pierre Auger collaboration (485 authors); Abreu, Pedro; Andringa, Sofia; Assis, Pedro; Brogueira, Pedro; Cazon, Lorenzo; Conceição, Ruben; Diogo, Francisco; Espadanal, Joao; Gonçalves, Patrícia; Oliveira, Micael; Pimenta, Mário; Santo, Catarina E; Santos, Eva; Sarmento, Raul; Tomé, Bernardo
We report a study of the distributions of the depth of maximum, Xmax, of extensive air-shower profiles with energies above 1017.8 eV as observed with the fluorescence telescopes of the Pierre Auger Observatory. The analysis method for selecting a data sample with minimal sampling bias is described in detail as well as the experimental cross-checks and systematic uncertainties. Furthermore, we discuss the detector acceptance and the resolution of the Xmax measurement and provide parametrizations thereof as a function of energy. The energy dependence of the mean and standard deviation of the Xmax distributions are compared to air-shower simulations for different nuclear primaries and interpreted in terms of the mean and variance of the logarithmic mass distribution at the top of the atmosphere.
- Energy Estimation of Cosmic Rays with the Engineering Radio Array of the Pierre Auger ObservatoryPublication . Pierre Auger collaboration (450 authors); Abreu, Pedro; Andringa, Sofia; Assis, Pedro; Blanco, Alberto; Brogueira, Pedro; Cazon, Lorenzo; Conceição, Ruben; Diogo, Francisco; Espadanal, Joao; Lopes, Luis; Pimenta, Mário; Santos, Eva; Sarmento, Raul; Tomé, BernardoThe 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 30–80 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.
- Identifying Clouds over the Pierre Auger Observatory using Infrared Satellite DataPublication . Pierre Auger collaboration (504 authors); Abreu, Pedro; Andringa, Sofia; Assis, Pedro; Brogueira, Pedro; Cazon, Lorenzo; Conceição, Ruben; Diogo, Francisco; Espadanal, Joao; Gonçalves, Patrícia; Oliveira, Micael; Pimenta, Mário; Santo, Catarina E; Santos, Eva; Tomé, BernardoWe describe a new method of identifying night-time clouds over the Pierre Auger Observatory using infrared data from the Imager instruments on the GOES-12 and GOES-13 satellites. We compare cloud identifications resulting from our method to those obtained by the Central Laser Facility of the Auger Observatory. Using our new method we can now develop cloud probability maps for the 3000 km^2 of the Pierre Auger Observatory twice per hour with a spatial resolution of ~2.4 km by ~5.5 km. Our method could also be applied to monitor cloud cover for other ground-based observatories and for space-based observatories.
- Improved limit to the diffuse flux of ultrahigh energy neutrinos from the Pierre Auger ObservatoryPublication . Pierre Auger collaboration (464 authors); Abreu, Pedro; Andringa, Sofia; Assis, Pedro; Blanco, Alberto; Brogueira, Pedro; Cazon, Lorenzo; Conceição, Ruben; Diogo, Francisco; Espadanal, Joao; Lopes, Luis; Pimenta, Mário; Santos, Eva; Sarmento, Raul; Tomé, BernardoNeutrinos in the cosmic ray flux with energies near 1 EeV and above are detectable with the Surface Detector array (SD) of the Pierre Auger Observatory. We report here on searches through Auger data from 1 January 2004 until 20 June 2013. No neutrino candidates were found, yielding a limit to the diffuse flux of ultrahigh energy neutrinos that challenges the Waxman-Bahcall bound predictions. Neutrino identification is attempted using the broad time structure of the signals expected in the SD stations, and is efficiently done for neutrinos of all flavors interacting in the atmosphere at large zenith angles, as well as for “Earth-skimming” neutrino interactions in the case of tau neutrinos. In this paper the searches for downward-going neutrinos in the zenith angle bins 60°–75° and 75°–90° as well as for upward-going neutrinos, are combined to give a single limit. The 90% C.L. single-flavor limit to the diffuse flux of ultrahigh energy neutrinos with an E-2 spectrum in the energy range 1.0×1017 eV–2.5×1019 eV is Eν2dNν/dEν<6.4×10−9 GeV cm−2 s−1 sr−1.
- Interpretation of the Depths of Maximum of Extensive Air Showers Measured by the Pierre Auger ObservatoryPublication . Pierre Auger collaboration (504 authors); Abreu, Pedro; Andringa, Sofia; Assis, Pedro; Brogueira, Pedro; Cazon, Lorenzo; Conceição, Ruben; Diogo, Francisco; Espadanal, Joao; Gonçalves, Patrícia; Oliveira, Micael; Pimenta, Mário; Santo, Catarina E; Santos, Eva; Tomé, BernardoTo interpret the mean depth of cosmic ray air shower maximum and its dispersion, we parametrize those two observables as functions of the first two moments of the ln A distribution. We examine the goodness of this simple method through simulations of test mass distributions. The application of the parameterization to Pierre Auger Observatory data allows one to study the energy dependence of the mean ln A and of its variance under the assumption of selected hadronic interaction models. We discuss possible implications of these dependences in term of interaction models and astrophysical cosmic ray sources.
- «
- 1 (current)
- 2
- 3
- »