Measurement of the Iron Spectrum in Cosmic Rays with VERITAS

TL;DR

This paper presents a novel measurement of the cosmic ray iron spectrum in the 20 TeV to 500 TeV range using VERITAS imaging air Cherenkov telescopes, employing advanced reconstruction and background estimation techniques.

Contribution

It introduces a new method for measuring the iron spectrum with IACTs, combining template likelihood fitting and Cherenkov light analysis for cosmic-ray physics.

Findings

Iron spectrum measured from 20 TeV to 500 TeV.

Used Cherenkov light and multivariate background estimation.

Demonstrated IACTs' capability for cosmic-ray elemental measurements.

Abstract

The elemental energy spectra of cosmic rays play an important role in understanding their acceleration and propagation. Most current results are obtained either from direct measurements by balloon or satellite detectors, or from indirect measurements by air shower detector arrays on the Earth's surface. Imaging Air Cherenkov Telescopes (IACTs), used primarily for gamma-ray astronomy, can also be used for cosmic-ray physics. They are able to measure Cherenkov light emitted both by heavy nuclei and by secondary particles produced in their air showers, and are thus sensitive to the charge and energy of cosmic ray particles with energies of tens to hundreds of TeV. A measurement of the energy spectrum of iron nuclei, based on 71 hours of data taken by the VERITAS array of IACTs between 2009 and 2012, will be presented. The energy and other properties of the primary particle are reconstructed using a template-based likelihood fit. The event selection makes use of direct Cherenkov light, which is emitted by the primary particle before starting the air shower. A multivariate method is used to estimate the remaining background. Using these methods, the iron spectrum was measured in the energy range from 20 TeV to 500 TeV.