The data collected by the Pierre Auger Observatory are analyzed to search for coincidences between the arrival directions of high-energy cosmic rays and the positions in the sky of astrophysical transients. Special attention is directed towards gamma ray observations recorded by NASA's Swift mission, which have an angular resolution similar to that of the Auger surface detectors. In particular, we check our data for evidence of a signal associated with the giant flare that came from the soft gamma repeater 1806-20 on December 27, 2004.
If clustering of the arrival directions of ultra high energy cosmic rays is discovered, this would provide important information about their origin, composition, and the galactic and extragalactic magnetic fields. We present here the analysis of the autocorrelation function of the data from the Pierre Auger Observatory as a function of the angular scale and the energy threshold. We compare our results with the signals found by previous experiments.
The precise determination of the arrival direction of cosmic rays is a fundamental prerequisite for the search for sources or the study of their anisotropies on the sky. One of the most important aspects to achieve an optimal measurement of these directions is to properly take into account the measurement uncertainties in the estimation procedure. In this article we present a model for the uncertainties associated with the time measurements in the Auger surface detector array. We show that this model represents well the measurement uncertainties and therefore provides the basis for an optimal …
The recent discovery by the Pierre Auger collaboration of anisotropy in the arrival directions of the highest energy cosmic rays, correlated with the positions of nearby active galactic nuclei, encourages the search for counterpart TeV gamma-ray emission. Approximately half of the sky viewed by the southern hemisphere Pierre Auger experiment is also visible at reasonable elevations for the northern hemisphere gamma-ray telescope array, VERITAS. We report on first observations by VERITAS of regions associated with the arrival directions of ultra-high energy cosmic ray events.
(abridged) The Pierre Auger Collaboration has reported 27 Ultra-High Energy Cosmic Ray Events (UHECRs) with energies above 56 EeV and well determined arrival directions as of 2007 August 31. They find that the arrival directions are not isotropic, but instead appear correlated with the positions of nearby AGNs. Our aim was to determine the sources of these UHECRs by comparing their arrival directions with more comprehensive source catalogs. Four (eight) of the 27 UHECRs with energy >56EeV detected by the Pierre Auger Observatory have arrival directions within 1.5deg (3.5deg) of the extended (>…
When searching for anisotropies in the arrival directions of Ultra High Energy Cosmic Rays, one must estimate the number of events expected in each direction of the sky in the case of a perfect isotropy. We present in this article a new method, developed for the Auger Observatory, based on a smooth estimate of the zenith angle distribution obtained from the data itself (which is essentially unchanged in the case of the presence of a large scale anisotropy pattern). We also study the sensitivity of several methods to detect large-scale anisotropies in the cosmic ray arrival direction distributi…
The Auger project was designed to study the high-energy cosmic rays by measuring the properties of the showers produced in the atmosphere. The Southern Auger Observatory has taken data since January 2004 and is now completed. Results on mass composition, energy spectrum and anisotropy of the arrival directions are presented together with upper limits on the neutrino fraction. The most important result is the recent observation of correlations with nearby extragalactic objects.
The Pierre Auger Observatory is a multi-national project for research on ultra-high energy cosmic rays. The Southern Auger Observatory in Mendoza province, Argentina, is approaching completion in 2007 with an instrumented area of 3,000 km^2. It will accurately measure the spectrum and composition of ultra-high energy cosmic rays up to and beyond the predicted GZK feature. We are obtaining results on the energy spectrum, mass composition and distribution of arrival directions on the southern sky. The Northern Auger Observatory is designed to complete and extend the investigations begun in the S…
We report a measurement of the cosmic ray energy spectrum obtained using the inclined events detected with the Pierre Auger Observatory. Showers with zenith angles between 60 and 80 degrees recorded in the period between 1 January 2004 and 28 February 2007 are analysed. Showers are first reconstructed in arrival direction and then fitted to density maps of the muon numbers obtained from 10 EeV simulated proton showers for different arrival directions, in order to obtain the core position and an overall normalisation factor N19 which is used as an energy estimator. The parameter N19 is shown to…
The Pierre Auger observatory has presented evidence that the arrival directions of cosmic rays with energies in excess of 6x10^7 TeV may be correlated with nearby active galactic nuclei (AGN). In this context we revisit a suggestion based on gamma ray observations that nearby Fanaroff-Riley I galaxies such as Cen A and M87 are the sources of the local cosmic rays. We compute the accompanying neutrino flux and find a flux within reach of second-generation kilometer-scale neutrino telescopes.
We present the status and the recent measurements from the Pierre Auger Observatory. The energy spectrum will be described and its steepening discussed. The mass composition is addressed with the measurements of the variation of the depth of shower maximum with energy. We also report on upper limits in the primary photon fraction. And finally, searches for anisotropies of cosmic rays arrival directions are reported.
The reconstruction of extensive air showers (arrival direction, core position and energy estimation) by the surface detector of the Pierre Auger Observatory is discussed together with the corresponding accuracy. We determine the angular reconstruction accuracy as a function of the station multiplicity by using two different aproaches. We discuss statistical and systematic uncertainties in the determination of the signal at 1000 m from the core, S(1000), which is used to estimate the primary energy.
The Pierre Auger Observatory, with an array of currently more than 1200 Cherenkov detectors filled with 12 m$^3$ of water, can detect the putative high energy emission of a GRB (photons down to a few hundreds of MeV) by the so-called ``single particle technique'', through a coherent increase in the average background particle rates over the whole array, due to secondary particles in the photon-induced showers. We present a search for bursts on data collected since September 2005, as well as a search for excesses in coincidence with bursts observed by satellites.
The focus of this article is on recent results on ultra-high energy cosmic rays obtained with the Pierre Auger Observatory. The world's largest instrument of this type and its performance are described. The observations presented here include the energy spectrum, the primary particle composition, limits on the fluxes of photons and neutrinos and a discussion of the anisotropic distribution of the arrival directions of the most energetic particles. Finally, plans for the construction of a Northern Auger Observatory in Colorado, USA, are discussed.
The Surface Detector of the Pierre Auger Observatory will consist of 1600 water Cherenkov tanks sampling ground particles of air showers produced by energetic cosmic rays. The arrival times are obtained from GPS and power is provided by solar panels. The construction of the array is nearly completed and a large number of detectors has been operational for more than three years. In this paper the performance of different components of the detectors are discussed. The accuracy of the signal measurement and the trigger stability are presented. The performance of the solar power system and other h…
More than two years of fluorescence detector data collected in coincidence with at least one station of the surface detector array (``hybrid data'') are used to measure the flux and energy spectrum of cosmic rays above about 10$^{18}$ eV. The hybrid measurement extends towards lower energies the spectrum measured with the surface detector data only, and provides a cross-check with an independent data set. The determination of the fluorescence detector aperture and of its live-time, which is the major aspect of this measurement, is illustrated in detail. Our current estimate of the correspondin…
The Southern Pierre Auger Observatory is now nearing completion and the accumulating data sample has already allowed to extract scientific results of relevance for ultra-high energy cosmic-ray (UHECR) physics. This lecture focuses on the description and outcomes of the studies on the UHECR arrival directions (and in particular the anisotropy searches around the Galactic Center) and composition (with the extraction of a limit on the flux of UHE photons and its implications). Perspectives concerning the study of inclined showers and the potential of detection of UHE neutrinos are also briefly di…
The goal of the Pierre Auger Observatory is to determine the still unknown nature and origin of ultra-high energy cosmic rays. The study of these elusive particles probes astrophysical sites of particle acceleration as well as fundamental interactions at energies unattainable in accelerator facilities. Auger combines two observational techniques, a large surface array and air fluorescence detectors, to observe the extended air showers generated in the atmosphere by cosmic rays. This hybrid observation yields an excellent resolution and allows for important cross-checks. The Auger South site, l…
We determine the instantaneous aperture and integrated exposure of the surface detector of the Pierre Auger Observatory, taking into account the trigger efficiency as a function of the energy, arrival direction (with zenith angle lower than 60 degrees) and nature of the primary cosmic-ray. We make use of the so-called Lateral Trigger Probability function (or LTP) associated with an extensive air shower, which summarizes all the relevant information about the physics of the shower, the water tank Cherenkov detector, and the triggers.
This paper presents the highlights from the recent measurements of the energy spectrum, mass composition, and arrival directions of the ultra-high energy ($> 10^{17}$ eV = 0.1 EeV) cosmic rays (UHECR) by the Pierre Auger Observatory. The Auger hybrid detector combines fluorescence observations of the longitudinal profiles of extended air showers, initiated by these extremely energetic particles, with measures of the shower secondaries at the ground level by its large array of Cherenkov water tanks. The complementariness of the two techniques provides important cross-checks at the energies unre…
The trigger system of the Surface Detector (SD) of the Pierre Auger Observatory is described, from the identification of candidate showers ($E>1$ EeV) at the level of a single station, among a huge background (mainly single muons), up to the selection of real events and the rejection of random coincidences at a higher central trigger level (including the reconstruction accuracy). Efficiency of a single station trigger is evaluated using real data , and the high performance of event selection hierarchy will be demonstrated.
The Pierre Auger Observatory is a``hybrid'' UHECR detector. The surface detector (SD) and air fluorescence detector (FD) of the observatory are designed for observation of cosmic ray showers in coincidence, with a 10% duty cycle. The resulting data are expected to be superior in quality to those of either the SD or FD operating individually. Hybrid operation, triggering, data acquisition, and event reconstruction were successfully demonstrated during the prototype phase of the project. This paper focuses on 75 hybrid events recorded during a four month period of running with the prototype dete…
The Pierre Auger Observatory has been designed to study the highest-energy cosmic rays in nature (E > 10^{18.5} eV). The determination of their arrival direction, energy and composition is performed by the analysis of the atmospheric showers they produce. The Auger Surface Array will consist of 1600 water Cerenkov detectors placed in an equilateral triangular grid of 1.5 km spacing. The aim of this paper is to show that the addition of a "small" area of surface detectors at half or less the above mentioned spacing would allow a dramatic increase of the physical scope of this Observatory, reach…
We study about ultra-high-energy cosmic rays (UHECRs) from transient sources, propagating in the Galactic and intergalactic space. Based on the recent observational results, we also estimate upper and lower bounds on the rate of transient UHECR sources and required isotropic cosmic-ray energy input per burst as 0.1 Gpc^-3 yr^-1 < rho_0 < 10^3.5 Gpc^-3 yr^-1 and 10^49.5 ergs < E_HECR^iso < 10^54 ergs, through constraining the apparent burst duration, i.e., dispersion in arrival times of UHECRs. Based on these bounds, we discuss implications for proposed candidates such as gamma-ray bursts and a…
The Pierre Auger Southern Observatory in Argentina has begun taking data as it is being developed up to a final enclosed area of 3000 square kilometres. A key aspect of the project is to provide information on the origin of the highest energy cosmic rays through understanding the arrival directions of those particles. To avoid claims of a spurious anisotropy detection because trials have not been properly accounted, the Auger Collaboration has agreed 'a priori' to the analysis prescription presented here. It specifies the following: 1. The accumulation time for the (future) data set to be anal…
We examine the anisotropy of the arrival directions of twenty seven ultra high energy cosmic rays detected by the Pierre Auger Collaboration. We confirm the anisotropy of the arrival directions of these events and find a significant correlation with the updated definition of the supergalactic plane at distances up to 70 Mpc, A Monte Carlo calculation of isotropic source distribution suggests a chance probability for isotropic event arrival direction distribution of 2-6$\times10^{-4}$.
The detectors of the surface array of the Pierre Auger Observatory are water Cherenkov tanks. The signals from each tank are read out using three photomultipliers. The energy of the primary particle is inferred from signal densities and requires good linearity of the PMTs and a large dynamic range. The absolute time of arrival of the shower front at each tank is obtained from the Global Positioning System (GPS) with a resolution of about 10 ns, ensuring an accurate primary angular reconstruction. Additionally, it is intended to use the rise time and shape of the signals to constrain the nature…
We discuss the anisotropic arrival directions of the ultra high energy cosmic rays detected by Auger which I consider one of the biggest discoverie in astrophysics during the last year.
The Pierre Auger Observatory data have been analyzed to search for excesses of events near the direction of the galactic center in several energy ranges around EeV energies. In this region the statistics accumulated by the Observatory are already larger than that of any previous experiment. Using both the data sets from the surface detector and our hybrid data sets (events detected simultaneously by the surface detector and the fluorescence detector) we do not find any significant excess. At our present level of undestanding of the performance and properties of our detector, our results do not…
The observation of cosmic ray particles with unexpected high energies is pushing astroparticle physics into a period of rapid progress both theoretically and experimentally. Different proposed models for the generation of these particles are constrained by the absence of the predicted GZK cutoff in the cosmic ray spectrum and by the composition and the distribution of arrival directions observed. The database increase due to the Pierre Auger Observatory will provide a clearer picture of the spectral anisotropy and properties of such high energy particles, enabling tests of their origin and nat…
Auger results on clustering of > 60 EeV ultra-high energy cosmic ray (UHECR) ions and the interpretation of the gamma-ray spectra of TeV blazars are connected by effects from the extragalactic background light (EBL). The EBL acts as an obscuring medium for gamma rays and a reprocessing medium for UHECR ions and protons, causing the GZK cutoff. The study of the physics underlying the coincidence between the GZK energy and the clustering energy of UHECR ions favors a composition of > 60 EeV UHECRs in CNO group nucleons. This has interesting implications for the sources of UHECRs. We also comment…
We measure the correlation between the arrival directions of the highest energy cosmic rays detected by the Pierre Auger Observatory with the position of the galaxies in the HI Parkes All Sky Survey (HIPASS) catalogue, weighted for their HI flux and Auger exposure. The use of this absorption-free catalogue, complete also along the galactic plane, allows us to use all the Auger events. The correlation is significant, being 86.2% for the entire sample of HI galaxies, and becoming 99% when considering the richest galaxies in HI content, or 98% with those lying between 40-55. We interpret this res…
The main technique that has been used to estimate the rate of gravitational wave (gw) bursts is to search for coincidence among times of arrival of candidate events in different detectors. Coincidences are modeled as a (possibly non-stationary) random time series background with gw events embedded in it, at random times but constant average rate. It is critical to test whether the statistics of the coincidence counts is Poisson, because the counts in a single detector often are not. At some point a number of parameters are tuned to increase the chance of detection by reducing the expected back…
The discoveries of the GZK cutoff with the HiRes and Auger Observatories and the discovery by Auger of clustering of >~60 EeV ultra-high energy cosmic rays (UHECRs) towards nearby <~75 Mpc) AGNs along the supergalactic plane establishes the astrophysical origin of the UHECRs. The likely sources of the UHECRs are gamma-ray bursts and radio-loud AGNs because: (1) they are extragalactic; (2) they are sufficiently powerful; (3) acceleration to ultra-high energies can be achieved in their relativistic ejecta; (4) anomalous X-ray and gamma-ray features can be explained by nonthermal hadron accelerat…
The arrival directions of extremely high energy cosmic rays (EHECR) above $4\times10^{19}$ eV, observed by four surface array experiments in the northern hemisphere,are examined for coincidences from similar directions in the sky. The total number of cosmic rays is 92.A significant number of double coincidences (doublet) and triple coincidences (triplet) are observed on the supergalactic plane within the experimental angular resolution. The chance probability of such multiplets from a uniform distribution is less than 1 % if we consider a restricted region within $\pm 10^{\circ}$ of the superg…
The southern Pierre Auger Observatory, presently under construction in Malarg"ue, Argentina, is nearing completion. The instrument is designed to measure extensive air-showers with energies ranging from $10^{18}$-$10^{20}$ eV and beyond. It combines two complementary observation techniques; the detection of particles at ground and the coincident observation of associated fluorescence light generated in the atmosphere above the ground. This is being realized by employing an array of 1600 water Cherenkov detectors, distributed over an area of 3000 km$^{2}$, and operating 24 wide-angle Schmidt te…
Firm evidence for a radio emission counterpart of cosmic ray air showers is presented. By the use of an antenna array set up in coincidence with ground particle detectors, we find a collection of events for which both time and arrival direction coincidences between particle and radio signals are observed. The counting rate corresponds to shower energies $\gtrsim 5\times 10^{16}$ eV. These results open overwhelming perspectives to complete existing detection methods for the observation of ultra high-energy cosmic rays.
In this review we discuss the important progress made in recent years towards understanding the experimental data on cosmic rays with energies $\agt 10^{19}$ eV. We begin with a brief survey of the available data, including a description of the energy spectrum, mass composition, and arrival directions. At this point we also give a short overview of experimental techniques. After that, we introduce the fundamentals of acceleration and propagation in order to discuss the conjectured nearby cosmic ray sources. We then turn to theoretical notions of physics beyond the Standard Model where we consi…
We measure the correlation between sky coordinates of the Swift BAT catalogue of active galactic nuclei with the arrival directions of the highest energy cosmic rays detected by the Auger Observatory. The statistically complete, hard X-ray catalogue helps to distinguish between AGN and other source candidates that follow the distribution of local large-scale structure. The positions of the full catalogue are marginally uncorrelated with the cosmic ray arrival directions, but when weighted by their hard X-ray flux, AGN within 100 Mpc are correlated at a significance level of 98 per cent. This c…
Decay or annihilation products of superheavy dark matter (SHDM) could be responsible for the end of the Ultra-High Energy Cosmic Ray (UHECR) spectrum. In this case, the south array of the Pierre Auger Observatory should observe in the future a significant anisotropy of UHECR arrival directions towards the galactic center. Here we use the already existing data of the SUGAR array to test this possibility. If decaying SHDM is distributed according a Navarro-Frenk-White (NFW) dark matter profile with core radius R_c=15 kpc and is responsible only for UHECRs above 6*10^{19} eV, i.e. the AGASA exces…
With the aim of testing recent claims for a particularly strong correlation between ultra-high energy cosmic rays (UHECRs), observed with the AGASA and the Yakutsk experiments, and a sample of BL Lacertae (BL Lacs), we here conduct a blind statistical assessment. We search for associations between the same set of BL Lac objects and the arrival directions of 33 relevant UHECRs observed with the Haverah Park and the Volcano Ranch experiments. Within the accuracy of angle determination, there are no positional coincidences. The probability that this null result arises as a statistical fluctuation…
