The Pierre Auger Observatory is the world’s largest operating detection system for the observation of ultra high energy cosmic rays (UHECRs), with energies above 10 17 eV. The detector allows ...detailed measurements of the energy spectrum, mass composition and arrival directions of primary cosmic rays in the energy range above 10 17 eV. The data collected at the Auger Observatory over the last decade show the suppression of the cosmic ray flux at energies above 4 × 10 19 eV. However, it is still unclear if this suppression is caused by the energy limitation of their sources or by the Greisen–Zatsepin–Kuzmin (GZK) cut-off. In such a case, UHECRs would interact with the microwave background (CMB), so that particles traveling long intergalactic distances could not have energies greater than 5 × 10 19 eV. The other puzzle is the origin of UHECRs. Some clues can be drawn from studying the distribution of their arrival directions. The recently observed dipole anisotropy has an orientation that indicates an extragalactic origin of UHECRs. The Auger surface detector array is also sensitive to showers due to ultra high energy neutrinos of all flavors and photons, and recent neutrino and photon limits provided by the Auger Observatory can constrain models of the cosmogenic neutrino production and exotic scenarios of the UHECRs origin, such as the decays of super heavy, non-standard-model particles. In this paper, the recent results on measurements of the energy spectrum, mass composition and arrival directions of cosmic rays, as well as future prospects are presented.
We 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 3000km2 of the Pierre Auger Observatory twice per hour with a spatial resolution of ∼2.4km by ∼5.5km. Our method could also be applied to monitor cloud cover for other ground-based observatories and for space-based observatories.
The measurement of radio signals from air showers is studied in detail with the Auger Engineering Radio Array (AERA) at the site of the Pierre Auger Observatory in Argentina. The first stage of AERA ...is in operation since March 2011 and consists of 24 autonomous radio detector stations. The design of the stations including the radio antennas, the electronics system and the communications system is presented. In the next 12 months AERA will grow to a size of 125 stations covering an area of about 16km2. First results and improvements for this next stage of AERA will be discussed.
The surface detector array of the Pierre Auger Observatory is sensitive to ultra-high energy neutrinos in the cosmic radiation. These particles can interact close to ground, both through charged and ...neutral currents in the atmosphere (down-going) and, for tau neutrinos, through the Earth-skimming mechanism (up-going) where a tau lepton is produced in the Earth's crust that can emerge and decay in the atmosphere. Both types of neutrino-induced events produce an inclined shower that can be identified by the presence of a broad time structure of signals in the water-Cherenkov detectors. Using data collected from the surface detector array of the Pierre Auger Observatory, we present the corresponding limits on the diffuse flux of ultra-high energy neutrinos.
Deployed at the end of 2010 at the Pierre Auger Observatory, the first stage of the Auger Engineering Radio Array, AERA24, consists of 24 radio stations covering an area of 0.5km2. AERA measures the ...radio emission from cosmic-ray induced air showers. The amplitude of this radio emission is used to constrain the characteristics of the primary particle: arrival direction, energy and nature. These studies are possible thanks to an instrumentation development allowing self-triggered and externally triggered measurements in the MHz domain and an improved understanding of radio emission processes. In May 2013, 100 new stations were installed to cover an area of ≃6km2, for a total of 124 stations. This stage 2 will provide higher statistics and will enhance both the estimate of the nature of the primary cosmic ray and the energy resolution above 1017 eV as an addition to detectors such as the Auger fluorescence telescopes and particle detectors. We will present the main results obtained with the stage 1 of AERA and the current status of the experiment. We will end with a brief overview of the GHz-experiments installed at the Pierre Auger Observatory.
The Pierre Auger Observatory explores the potential of radio-detection techniques to measure extensive air showers (EAS) induced by ultra-high energy cosmic rays. To study in detail the mechanisms ...responsible for radio emission in the MHz range, the Auger Engineering Radio Array has been installed at the Observatory. Presently consisting of 24 radio-detection stations, this number will grow to 150 units covering an area of almost 20km2. Novel detection techniques based on the GHz emission from the EAS are currently being studied. AMBER (Air-shower Microwave Bremsstrahlung Experimental Radiometer) and MIDAS (Microwave Detection of Air Showers) are prototypes for a large imaging dish antenna. In EASIER (Extensive Air Shower Identification using Electron Radiometer), the microwave emission is detected by antenna horns located on each surface detector. MIDAS is a self-triggering system while AMBER and EASIER use the trigger from the Auger detectors to record the emission. The status of these radio-detection R&D efforts at the Pierre Auger Observatory will be reported.
The Pierre Auger Observatory is an experiment aimed at the measurement of Extensive Air Showers produced by the Ultra-High Energy Cosmic Rays. It consists of a surface array, which measures the ...shower particles at ground level, and a fluorescence detector, which observes the development of showers above the array. The measurement of the spectrum of Ultra-High Energy Cosmic Rays using fluorescence observations in coincidence with at least one water Cherenkov detector of the array is reported. In particular, the derivation of the corresponding exposure, which is the main ingredient of the calculation of this spectrum, is discussed. The spectrum based only on the surface array data is also described. Finally, the combination of the two spectra, as well as the systematic uncertainties of the combined spectrum is addressed.
Radio detection provides information about the electromagnetic part of an air shower in the atmosphere complementary to that obtained by water-Cherenkov detectors predominantly sensitive to the ...muonic content of an air shower at ground. For the measurement of ultra-high-energy cosmic rays (UHECR) by the detection of their coherent radio emission, several test setups have been developed and deployed at the Pierre Auger Observatory in Argentina. However, these UHECR radio pulses are significantly polluted by man-made radio frequency interferences (RFI). This requires a special design of antennas, analog, data acquisition (DAQ), and communication electronics, which are under investigation at the Pierre Auger Observatory. In large-scale detector arrays sophisticated self-triggering methods are necessary, to use the limited available communication data rate efficiently. This paper gives an overview of the electronics and self-triggering methods used in the test setups at the Pierre Auger Observatory and describes the experiences gained so far.
Completed at the end of 2008, the Pierre Auger Observatory has been continuously operating for more than seven years. We present here the analysis techniques and the results about the search for ...large scale anisotropies in the sky distribution of cosmic rays, reporting both the phase and the amplitude measurements of the first harmonic modulation in right ascension in different energy ranges above 2.5×1017eV. Thanks to the collected statistics, a sensitivity of 1% at EeV energies can be reached. No significant anisotropies have been observed, upper limits on the amplitudes have been derived and are here compared with the results of previous experiments and with some theoretical expectations.
Ultra-high energy cosmic rays generate extensive air showers in Earth’s atmosphere. A standard approach to reconstruct the energy of an ultra-high energy cosmic rays is to sample the lateral profile ...of the particle density on the ground of the air shower with an array of surface detectors.
For cosmic rays with large inclinations, this reconstruction is based on a model of the lateral profile of the muon density observed on the ground, which is fitted to the observed muon densities in individual surface detectors. The best models for this task are derived from detailed Monte-Carlo simulations of the air shower development. We present a phenomenological parametrization scheme which allows to derive a model of the average lateral profile of the muon density directly from a fit to a set of individual Monte-Carlo simulated air showers. The model reproduces the detailed simulations with a high precision. As an example, we generate a muon density model which is valid in the energy range 10
18
eV
<
E
<
10
20
eV and the zenith angle range
60
°
<
θ
<
90
°
.
We will further demonstrate a way to speed up the simulation of such muon profiles by three orders of magnitude, if only the muons in the shower are of interest.
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