Radio-detection of extensive air showers at the Pierre Auger Observatory - Results and enhancements

The Pierre Auger Collaboration is exploring the potential of radio-detection techniques to measure the extensive air showers. The main advantage of these setups is the possibility to cover a large area with no atmospheric attenuation and having 100% duty cycle. Radio emission in the MHz range is recorded by the Auger Engineering Radio Array (AERA), presently consisting of 124 stations distributed over an area of approximately 6 km$^2$. This enhancement is focused on physics of cosmic rays with an energy greater than 10$^{17}$ eV. In addition, novel detection techniques based on the GHz emission from extensive air showers are being tested at the Pierre Auger Observatory. Three different setups are currently installed and are collecting data: MIDAS (Microwave Detection of Air Showers) and AMBER (Air-shower Microwave Bremsstrahlung Experimental Radiometer) are prototypes of an imaging parabolic dish detector, while EASIER (Extensive Air Shower Identification using Electron Radiometer) records the radio emission by antenna horns located on more than 60 surface detector units. The status of these different activities and the new results in MHz and GHz bands will be reported.Comment: 3 pages -- EPS-HEP'13 European Physical Society Conference on High Energy Physics (July, 18-24, 2013) at Stockholm, Swede

Monte Carlo simulation of multiple scattered light in the atmosphere

We present a Monte Carlo simulation for the scattering of light in the case of an isotropic light source. The scattering phase functions are studied particularly in detail to understand how they can affect the multiple light scattering in the atmosphere. We show that although aerosols are usually in lower density than molecules in the atmosphere, they can have a non-negligible effect on the atmospheric point spread function. This effect is especially expected for ground-based detectors when large aerosols are present in the atmosphere.Comment: 5 pages. Proceedings of the Atmospheric Monitoring for High-Energy Astroparticle Detectors (AtmoHEAD) Conference, Saclay (France), June 10-12, 201

Atmospheric multiple scattering of fluorescence light from extensive air showers and effect of the aerosol size on the reconstruction of energy and depth of maximum

The reconstruction of the energy and the depth of maximum $X_{\rm max}$ of an extensive air shower depends on the multiple scattering of fluorescence photons in the atmosphere. In this work, we explain how atmospheric aerosols, and especially their size, scatter the fluorescence photons during their propagation. Using a Monte Carlo simulation for the scattering of light, the dependence on the aerosol conditions of the multiple scattered light contribution to the recorded signal is fully parameterised. A clear dependence on the aerosol size is proposed for the first time. Finally, using this new parameterisation, the effect of atmospheric aerosols on the energy and on the $X_{\rm max}$ reconstructions is presented for a vertical extensive air shower observed by a ground-based detector at $30~$km: for typical aerosol conditions, multiple scattering leads to a systematic over-estimation of $5\pm1.5\%$ for the energy and $4.0\pm 1.5~$g/cm$^2$ for the $X_{\rm max}$, where the uncertainties refer to a variation of the aerosol size.Comment: 12 pages, 9 figures, journal paper, accepted in Astroparticle Physics. arXiv admin note: text overlap with arXiv:1310.170

Atmospheric considerations for CTA site search using global models

The Cherenkov Telescope Array (CTA) will be the next high-energy gamma-ray observatory. Selection of the sites, one in each hemisphere, is not obvious since several factors have to be taken into account. Among them, and probably the most crucial, are the atmospheric conditions. Indeed, CTA will use the atmosphere as a giant calorimeter, i.e. as part of the detector. The Southern Hemisphere presents mainly four candidate sites: one in Namibia, one in Chile and two in Argentina. Using atmospheric tools already validated in other air shower experiments, the purpose of this work is to complete studies aiming to choose the site with the best quality for the atmosphere. Three strong requirements are checked: the cloud cover and the frequency of clear skies, the wind speed and the backward trajectories of air masses travelling above the sites and directly linked to the aerosol concentrations. It was found, that the Namibian site is favoured, and one site in Argentina is clearly not suited. Atmospheric measurements at these sites will be performed in the coming months and will help with the selection of a CTA site.Comment: 4 pages, 4 figures, ECRS'12 - 23rd European Cosmic Ray Symposium (July, 3-7, 2012) at Mosco

Ramsauer approach for light scattering on non-absorbing spherical particles and application to the Henyey-Greenstein phase function

We present a new method to study light scattering on non-absorbing spherical particles. This method is based on the Ramsauer approach, a model known in atomic an nuclear physics. Its main advantage is its intuitive understanding of the underlying physics phenomena. We show that although the approximations are numerous, the Ramsauer analytical solutions describe fairly well the scattering phase function and the total cross section. Then this model is applied to the Henyey-Greenstein parameterisation of scattering phase function to give a relation between its asymmetry parameter and the mean particle size.Comment: 25 pages, 12 figures, journal paper, accepted in Applied Optics. arXiv admin note: text overlap with arXiv:0903.297

Atmospheric Monitoring at the Pierre Auger Observatory - Status and Update

International audienceCalorimetric measurements of extensive air showers are performed with the uorescence detector of the PierreAuger Observatory. To correct these measurements for the effects introduced by atmospheric uctuations, the Observa-tory operates several instruments to record atmospheric conditions across and above the detector site. New developmentshave been made in the study of the aerosol optical depth, the aerosol phase function and cloud identication. Also,for cosmic ray events meeting certain criteria, a rapid monitoring program has been developed to improve the accuracyof the reconstruction. We present an updated overview of performed measurements and their application to air shower reconstruction

Atmospheric effects in astroparticle physics experiments and the challenge of ever greater precision in measurements

Astroparticle physics and cosmology allow us to scan the universe through multiple messengers. It is the combination of these probes that improves our understanding of the universe, both in its composition and its dynamics. Unlike other areas in science, research in astroparticle physics has a real originality in detection techniques, in infrastructure locations, and in the observed physical phenomenon that is not created directly by humans. It is these features that make the minimisation of statistical and systematic errors a perpetual challenge. In all these projects, the environment is turned into a detector medium or a target. The atmosphere is probably the environment component the most common in astroparticle physics and requires a continuous monitoring of its properties to minimise as much as possible the systematic uncertainties associated. This paper introduces the different atmospheric effects to take into account in astroparticle physics measurements and provides a non-exhaustive list of techniques and instruments to monitor the different elements composing the atmosphere. A discussion on the close link between astroparticle physics and Earth sciences ends this paper.Comment: 27 pages, 8 figures, review paper, submitted to Astroparticle Physic

Origin of atmospheric aerosols at the Pierre Auger Observatory using backward trajectory of air masses

The Pierre Auger Observatory is the largest operating cosmic ray observatory ever built. Calorimetric measurements of extensive air showers induced by cosmic rays are performed with a fluorescence detector. Thus, one of the main challenges is the monitoring of the atmosphere, both in terms of atmospheric state variables and optical properties. To better understand the atmospheric conditions, a study of air mass trajectories above the site is presented. Such a study has been done using an air-modelling program well known in atmospheric sciences. Its validity has been checked using meteorological radiosonde soundings performed at the Pierre Auger Observatory. Finally, aerosol concentration values measured by the Central Laser Facility are compared to backward trajectories.Comment: 4 pages, 6 figures -- ECRS'12 European Cosmic Ray Symposium (July, 3-7, 2012) at Moscow, Russi

Atmospheric aerosols at the Pierre Auger Observatory and environmental implications

The Pierre Auger Observatory detects the highest energy cosmic rays. Calorimetric measurements of extensive air showers induced by cosmic rays are performed with a fluorescence detector. Thus, one of the main challenges is the atmospheric monitoring, especially for aerosols in suspension in the atmosphere. Several methods are described which have been developed to measure the aerosol optical depth profile and aerosol phase function, using lasers and other light sources as recorded by the fluorescence detector. The origin of atmospheric aerosols traveling through the Auger site is also presented, highlighting the effect of surrounding areas to atmospheric properties. In the aim to extend the Pierre Auger Observatory to an atmospheric research platform, a discussion about a collaborative project is presented.Comment: Regular Article, 16 pages, 12 figure

Ramsauer approach to Mie scattering of light on spherical particles

The scattering of an electromagnetic plane wave by a spherical particle was solved analytically by Gustav Mie in 1908. The Mie solution is expressed as a series with very many terms thus obscuring the physical interpretations of the results. The purpose of the paper is to try to illustrate this phenomenon within the Ramsauer framework used in atomic and nuclear physics. We show that although the approximations are numerous, the Ramsauer analytical formulae describe fairly well the differential and the total cross sections. This allows us to propose an explanation for the origin of the different structures in the total cross section