Spectral Calibration of the Fluorescence Telescopes of the Pierre Auger Observatory

TL;DR

This paper introduces a precise spectral calibration method for the Pierre Auger Observatory's fluorescence telescopes using a portable xenon flasher and monochromator, improving calibration accuracy and understanding its impact on measurements.

Contribution

A novel end-to-end spectral calibration technique using a portable light source and monochromator for fluorescence telescopes, enhancing precision over previous methods.

Findings

Achieved 1.5% spectral response calibration uncertainty for most telescopes.

Older telescopes have about 2.2% calibration uncertainty.

Calibration changes have minimal impact on physics measurements.

Abstract

We present a novel method to measure precisely the relative spectral response of the fluorescence telescopes of the Pierre Auger Observatory. We used a portable light source based on a xenon flasher and a monochromator to measure the relative spectral efficiencies of eight telescopes in steps of 5 nm from 280 nm to 440 nm. Each point in a scan had approximately 2 nm FWHM out of the monochromator. Different sets of telescopes in the observatory have different optical components, and the eight telescopes measured represent two each of the four combinations of components represented in the observatory. We made an end-to-end measurement of the response from different combinations of optical components, and the monochromator setup allowed for more precise and complete measurements than our previous multi-wavelength calibrations. We find an overall uncertainty in the calibration of the spectral response of most of the telescopes of 1.5% for all wavelengths; the six oldest telescopes have larger overall uncertainties of about 2.2%. We also report changes in physics measureables due to the change in calibration, which are generally small.