Abstract
The Pierre Auger Observatory’s Fluorescence Detector (FD) consists of 27 telescopes arranged in four sites around the perimeter of the 3000 square kilometre Surface Detector (SD). Cosmic ray extensive air showers are viewed via the nitrogen fluorescence light they induce in the atmosphere. Careful treatment of light attenuation processes must be made, especially given that some showers are viewed at distances in excess of 30 km. Of particular importance is the attenuation due to scattering by aerosol particles, a challenging topic given that aerosol concentrations can vary on time-scales of hours. At the Auger Observatory, the vertical distribution of aerosols is measured hourly with a series of bi-static lidar systems (consisting of central laser facilities and each of the FD sites), and three times per night with a Raman lidar system. In this contribution we describe the use of aerosol profiles in the analysis of air shower data, in particular in the estimation of the cosmic ray primary energy, and the depth of shower maximum, Xmax. We also demonstrate how statistical and systematic uncertainties in the aerosol concentrations propagate through to a contribution to energy and Xmax uncertainties.
Highlights
An observatory for ultra-high energy cosmic rays (UHECRs) requires an enormous collecting area and reliable methods for assigning arrival directions, energy and estimates of primary mass
The Pierre Auger Observatory’s Fluorescence Detector (FD) consists of 27 telescopes arranged in four sites around the perimeter of the 3000 square kilometre Surface Detector (SD)
Cosmic ray extensive air showers are viewed via the nitrogen fluorescence light they induce in the atmosphere
Summary
An observatory for ultra-high energy cosmic rays (UHECRs) requires an enormous collecting area and reliable methods for assigning arrival directions, energy and estimates of primary mass. The Observatory is located in western Argentina in the province of Mendoza on an elevated plain with an altitude of approximately 1400 m [1] The atmosphere is both the target for the incoming primary cosmic rays and the detection medium. The extensive air shower (EAS) initiated by the cosmic ray has a footprint at ground level of tens of square kilometres allowing for SD estimates of arrival direction and energy. The longitudinal development of the EAS may be observed with the FD via nitrogen fluorescence light. This rather weak light signal (at least compared with Cherenkov light) is emitted isotropically and in proportion to the ionisation energy deposited by the shower in the atmosphere.
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