arXiv subjects

O. Deligny

Publications and source records attributed to O. Deligny.

115 records · Page 7Linked to original sources

arXiv2014

A Targeted Search for Point Sources of EeV Neutrons

A 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.

astro-ph.HE↗

arXiv2014

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° 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.

astro-ph.HE↗

arXiv2013

Mass Composition Working Group Report at UHECR-2012

We present a summary of the measurements of mass sensitive parameters at the highest cosmic ray energies done by several experiments. The Xmax distribution as a function of energy has been measured with fluorescence telescopes by the HiRes, TA and Auger experiments and with Cherenkov light detectors by Yakutsk. The or the average mass ( ) has been also inferred using ground detectors, such as muon and water Cherenkov detectors. We discuss the different data analyses elaborated by each collaboration in order to extract the relevant information. Special attention is given to the different approaches used in the analysis of the data measured by fluorescence detectors in order to take into account detector biases. We present a careful analysis of the stability and performance of each analysis. The results of the different experiments will be compared and the discrepancies or agreements will be quantified.

astro-ph.HE↗

arXiv2011

The East-West method: an exposure-independent method to search for large scale anisotropies of cosmic rays

The measurement of large scale anisotropies in cosmic ray arrival directions at energies above 10^13 eV is performed through the detection of Extensive Air Showers produced by cosmic ray interactions in the atmosphere. The observed anisotropies are small, so accurate measurements require small statistical uncertainties, i.e. large datasets. These can be obtained by employing ground detector arrays with large extensions (from 10^4 to 10^9 m^2) and long operation time (up to 20 years). The control of such arrays is challenging and spurious variations in the counting rate due to instrumental effects (e.g. data taking interruptions or changes in the acceptance) and atmospheric effects (e.g. air temperature and pressure effects on EAS development) are usually present. These modulations must be corrected very precisely before performing standard anisotropy analyses, i.e. harmonic analysis of the counting rate versus local sidereal time. In this paper we discuss an alternative method to measure large scale anisotropies, the "East-West method", originally proposed by Nagashima in 1989. It is a differential method, as it is based on the analysis of the difference of the counting rates in the East and West directions. Besides explaining the principle, we present here its mathematical derivation, showing that the method is largely independent of experimental effects, that is, it does not require corrections for acceptance and/or for atmospheric effects. We explain the use of the method to derive the amplitude and phase of the anisotropy and we demonstrate its power under different conditions of detector operation.

astro-ph.IM↗

arXiv2009

The propagation of ultra-high energy tau leptons and neutrinos while skimming the Earth

The detection of Earth-skimming tau neutrinos has turned into a very promising strategy for the observation of UHE cosmic neutrinos. The sensitivity of this channel crucially depends on the parameters of the propagation of the tau neutrino (and the tau lepton) through the terrestrial crust, which governs the flux of emerging tau leptons that can be detected. This propagation problem is usually treated in a simplified framework where several effects are neglected, e.g. the possibility of multiple regenerations of the tau neutrino, the weak interactions of the tau lepton, as well as the stochastic nature of its energy losses. We discuss here the validity of such approximations by studying the propagation in standard rock of tau leptons and neutrinos with both mono-energetic and power-law spectra. We also investigate the impact of such simplifications in non-standard scenarios for the neutrino-nucleon interactions as well as for the tau energy losses.

hep-ph↗

arXiv2004

Angular Power Spectrum Estimation of Cosmic Ray Anisotropies with Full or Partial Sky Coverage

We study the angular power spectrum estimate in order to search for large scale anisotropies in the arrival directions distribution of the highest-energy cosmic rays. We show that this estimate can be performed even in the case of partial sky coverage and validated over the full sky under the assumption that the observed fluctuations are statistically spatial stationary. If this hypothesis - which can be tested directly on the data - is not satisfied, it would prove, of course, that the cosmic ray sky is non isotropic but also that the power spectrum is not an appropriate tool to represent its anisotropies, whatever the sky coverage available. We apply the method to simulations of the Pierre Auger Observatory, reconstructing an input power spectrum with the Southern site only and with both Northern and Southern ones. Finally, we show the improvement that a full-sky observatory brings to test an isotropic distribution, and we discuss the sensitivity of the Pierre Auger Observatory to large scale anisotropies.

astro-ph↗

arXiv2001

Tau Neutrinos in the Auger Observatory : A New Window to UHECR Sources

The cosmic ray spectrum has been shown to extend well beyond 10^{20}eV. With nearly 20 events observed in the last 40 years, it is now established that particles are accelerated or produced in the universe with energies near 10^{21}eV. In all production models neutrinos and photons are part of the cosmic ray flux. In acceleration models (bottom-up models), they are produced as secondaries of the possible interactions of the accelerated charged particle; in direct production models (top-down models) they are a dominant fraction of the decay chain. In addition, hadrons above the GZK threshold energy will also produce, along their path in the Universe, neutrinos and photons as secondaries of the pion photo-production processes. Therefore, photons and neutrinos are very distinctive signatures of the nature and distribution of the potential sources of ultra high energy cosmic rays. In the following we describe the tau neutrino detection and identification capabilities of the Auger observatory. We show that in the range 3x10^{17}-3x10^{20}eV the Auger effective apperture reaches a few tenths of km^2.sr, making the observatory sensitive to fluxes as low as a few tau neutrinos per km^2.sr.year. In the hypothesis of nu_mu <-->nu_tau oscillations with full mixing, this sensitivity allows to probe the GZK cutoff as well as to provide model independent constraints on the mechanisms of production of ultra high energy cosmic rays.

astro-ph↗