Observation of Ultra-high-energy Cosmic Rays with the ANITA Balloon-borne Radio Interferometer

TL;DR

This paper reports the detection of sixteen ultra-high-energy cosmic ray events using a balloon-borne radio interferometer, providing new measurements of radio emission from cosmic ray air showers in Antarctica.

Contribution

First ultra-wideband, far-field measurements of geosynchrotron radio emission from cosmic rays in the 300-1000 MHz range.

Findings

Radio emission is 100% linearly polarized.

Most events show phase-inversion due to ice reflection.

Detection of cosmic rays from above the horizon.

Abstract

We report the observation of sixteen cosmic ray events of mean energy of 1.5 x 10^{19} eV, via radio pulses originating from the interaction of the cosmic ray air shower with the Antarctic geomagnetic field, a process known as geosynchrotron emission. We present the first ultra-wideband, far-field measurements of the radio spectral density of geosynchrotron emission in the range from 300-1000 MHz. The emission is 100% linearly polarized in the plane perpendicular to the projected geomagnetic field. Fourteen of our observed events are seen to have a phase-inversion due to reflection of the radio beam off the ice surface, and two additional events are seen directly from above the horizon.