Energy and Flux Measurements of Ultra-High Energy Cosmic Rays Observed During the First ANITA Flight

TL;DR

This paper reports the first measurements of ultra-high energy cosmic rays using the ANITA experiment, estimating their energies, flux, and validating the detection method through simulations.

Contribution

It provides the first estimation of cosmic-ray flux solely from radio observations and validates the Monte Carlo simulation against observed data.

Findings

Mean cosmic-ray energy estimated at 2.9 EeV.

Monte Carlo simulations agree with observed event properties.

First radio-based cosmic-ray flux estimation.

Abstract

The first flight of the Antarctic Impulsive Transient Antenna (ANITA) experiment recorded 16 radio signals that were emitted by cosmic-ray induced air showers. For 14 of these events, this radiation was reflected from the ice. The dominant contribution to the radiation from the deflection of positrons and electrons in the geomagnetic field, which is beamed in the direction of motion of the air shower. This radiation is reflected from the ice and subsequently detected by the ANITA experiment at a flight altitude of 36km. In this paper, we estimate the energy of the 14 individual events and find that the mean energy of the cosmic-ray sample is 2.9 EeV. By simulating the ANITA flight, we calculate its exposure for ultra-high energy cosmic rays. We estimate for the first time the cosmic-ray flux derived only from radio observations. In addition, we find that the Monte Carlo simulation of the ANITA data set is in agreement with the total number of observed events and with the properties of those events.