34 research outputs found
Techniques for measuring aerosol attenuation using the Central Laser Facility at the Pierre Auger Observatory
The Pierre Auger Observatory in Malargüe, Argentina, is designed to study the properties of ultra-high energy cosmic rays with energies above 10(18) eV. It is a hybrid facility that employs a Fluorescence Detector to perform nearly calorimetric measurements of Extensive Air Shower energies. To obtain reliable calorimetric information from the FD, the atmospheric conditions at the observatory need to be continuously monitored during data acquisition. In particular, light attenuation due to aerosols is an important atmospheric correction. The aerosol concentration is highly variable, so that the aerosol attenuation needs to be evaluated hourly. We use light from the Central Laser Facility, located near the center of the observatory site, having an optical signature comparable to that of the highest energy showers detected by the FD. This paper presents two procedures developed to retrieve the aerosol attenuation of fluorescence light from CLF laser shots. Cross checks between the two methods demonstrate that results from both analyses are compatible, and that the uncertainties are well understood. The measurements of the aerosol attenuation provided by the two procedures are currently used at the Pierre Auger Observatory to reconstruct air shower data
Ultrahigh-energy neutrino follow-up of gravitational wave events GW150914 and GW151226 with the Pierre Auger Observatory
The rapid atmospheric monitoring system of the Pierre Auger Observatory
The Pierre Auger Observatory is a facility built to detect air showers produced by cosmic rays above 10(17) eV. During clear nights with a low illuminated moon fraction, the UV fluorescence light produced by air showers is recorded by optical telescopes at the Observatory. To correct the observations for variations in atmospheric conditions, atmospheric monitoring is performed at regular intervals ranging from several minutes (for cloud identification) to several hours (for aerosol conditions) to several days (for vertical profiles of temperature, pressure, and humidity). In 2009, the monitoring program was upgraded to allow for additional targeted measurements of atmospheric conditions shortly after the detection of air showers of special interest, e. g., showers produced by very high-energy cosmic rays or showers with atypical longitudinal profiles. The former events are of particular importance for the determination of the energy scale of the Observatory, and the latter are characteristic of unusual air shower physics or exotic primary particle types. The purpose of targeted (or 'rapid') monitoring is to improve the resolution of the atmospheric measurements for such events. In this paper, we report on the implementation of the rapid monitoring program and its current status. The rapid monitoring data have been analyzed and applied to the reconstruction of air showers of high interest, and indicate that the air fluorescence measurements affected by clouds and aerosols are effectively corrected using measurements from the regular atmospheric monitoring program. We find that the rapid monitoring program has potential for supporting dedicated physics analyses beyond the standard event reconstruction
Trigger and Aperture of the Surface Detector Array of the Pierre Auger Observatory
The surface detector array of the Pierre Auger Observatory consists of 1600
water-Cherenkov detectors, for the study of extensive air showers (EAS)
generated by ultra-high-energy cosmic rays. We describe the trigger hierarchy,
from the identification of candidate showers at the level of a single detector,
amongst a large background (mainly random single cosmic ray muons), up to the
selection of real events and the rejection of random coincidences. Such trigger
makes the surface detector array fully efficient for the detection of EAS with
energy above eV, for all zenith angles between 0 and
60, independently of the position of the impact point and of the mass
of the primary particle. In these range of energies and angles, the exposure of
the surface array can be determined purely on the basis of the geometrical
acceptance.Comment: 29 pages, 12 figure
The Rapid Atmospheric Monitoring System of the Pierre Auger Observatory
The Pierre Auger Observatory is a facility built to detect air showers
produced by cosmic rays above 10^17 eV. During clear nights with a low
illuminated moon fraction, the UV fluorescence light produced by air showers is
recorded by optical telescopes at the Observatory. To correct the observations
for variations in atmospheric conditions, atmospheric monitoring is performed
at regular intervals ranging from several minutes (for cloud identification) to
several hours (for aerosol conditions) to several days (for vertical profiles
of temperature, pressure, and humidity). In 2009, the monitoring program was
upgraded to allow for additional targeted measurements of atmospheric
conditions shortly after the detection of air showers of special interest,
e.g., showers produced by very high-energy cosmic rays or showers with atypical
longitudinal profiles. The former events are of particular importance for the
determination of the energy scale of the Observatory, and the latter are
characteristic of unusual air shower physics or exotic primary particle types.
The purpose of targeted (or "rapid") monitoring is to improve the resolution of
the atmospheric measurements for such events. In this paper, we report on the
implementation of the rapid monitoring program and its current status. The
rapid monitoring data have been analyzed and applied to the reconstruction of
air showers of high interest, and indicate that the air fluorescence
measurements affected by clouds and aerosols are effectively corrected using
measurements from the regular atmospheric monitoring program. We find that the
rapid monitoring program has potential for supporting dedicated physics
analyses beyond the standard event reconstruction
Evidence for a mixed mass composition at the ‘ankle’ in the cosmic-ray spectrum
We report a first measurement for ultrahigh energy cosmic rays of the correlation between the depth of shower maximum and the signal in the water Cherenkov stations of air-showers registered simultaneously by the fluorescence and the surface detectors of the Pierre Auger Observatory. Such a correlation measurement is a unique feature of a hybrid air-shower observatory with sensitivity to both the electromagnetic and muonic components. It allows an accurate determination of the spread of primary masses in the cosmic-ray flux. Up till now, constraints on the spread of primary masses have been dominated by systematic uncertainties. The present correlation measurement is not affected by systematics in the measurement of the depth of shower maximum or the signal in the water Cherenkov stations. The analysis relies on general characteristics of air showers and is thus robust also with respect to uncertainties in hadronic event generators. The observed correlation in the energy range around the \u2018ankle\u2019 at lg\u2061(E/eV)=18.5\u201319.0 differs significantly from expectations for pure primary cosmic-ray compositions. A light composition made up of proton and helium only is equally inconsistent with observations. The data are explained well by a mixed composition including nuclei with mass A>4. Scenarios such as the proton dip model, with almost pure compositions, are thus disfavored as the sole explanation of the ultrahigh-energy cosmic-ray flux at Earth
A Targeted Search for Point Sources of EeV Photons with the Pierre Auger Observatory
Simultaneous measurements of air showers with the fluorescence and surface detectors of the Pierre Auger Observatory allow a sensitive search for EeV photon point sources. Several Galactic and extragalactic candidate objects are grouped in classes to reduce the statistical penalty of many trials from that of a blind search and are analyzed for a significant excess above the background expectation. The presented search does not find any evidence for photon emission at candidate sources, and combined p-values for every class are reported. Particle and energy flux upper limits are given for selected candidate sources. These limits significantly constrain predictions of EeV proton emission models from non-transient Galactic and nearby extragalactic sources, as illustrated for the particular case of the Galactic center region
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 Pierre Auger Observatory status and latest results
The Pierre Auger Observatory, in Argentina, is the present flagship experiment studying ultrahigh-energy cosmic rays (UHECRs). Facing the challenge due to low cosmic-ray flux at the highest energies, the Observatory has been taking data for more than a decade, reaching an exposure of over 50 000 km2sr yr. The combination of a large surface detector array and fluorescence telescopes provides a substantial improvement in energy calibration and extensive air shower measurements, resulting in data of unprecedented quality. Moreover, the installation of a denser subarray has allowed extending the sensitivity to lower energies. Altogether, this contributes to provide important information on key questions in the UHECR field in the energy range from 0.1 EeV up to 100 EeV. A review of main results from the Pierre Auger Observatory is presented with a particular focus on the energy spectrum measurements, the mass composition studies, the arrival directions analyses, the search for neutral cosmic messengers, and the investigation of high-energy hadronic interactions. Despite this large amount of valuable results, the understanding of the nature of UHECRs and of their origin remains an open science case that the Auger collaboration is planning to address with the AugerPrime project to upgrade the Observatory
The Pierre Auger Observatory Upgrade
It is planned to operate the Pierre Auger Observatory until at least the end of 2024. An upgrade of the experiment has been proposed in order to provide additional measurements to allow one to elucidate the mass composition and the origin of the flux suppression at the highest energies, to search for a flux contribution of protons up to the highest energies and to reach a sensitivity to a contribution as small as 10% in the flux suppression region, to study extensive air showers and hadronic multi-particle production. With operation planned until 2024, event statistics will more than double compared with the existing Auger data set, with the critical added advantage that every event will now have mass information. Obtaining additional composition-sensitive information will not only help to better reconstruct the properties of the primary particles at the highest energies, but also improve the measurements in the energy range just above the ankle. Furthermore, measurements with the new detectors will help to reduce systematic uncertainties related to the modelling hadronic showers and to limitations in the reconstruction algorithms. A description of the principal proposed Auger upgrade will be presented. The Auger upgrade promises high-quality future data, and real scope for new physics