Dr. Kimberly Palladino

Abstract:

The first flight of the Antarctic Impulsive Transient Antenna (ANITA) experiment recorded 14 radio signals that were emitted by downward going cosmic-ray induced air showers. The dominant contribution to the radiation comes from the deflection of positrons and electrons in the geomagnetic field and is beamed in a cone around 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 -36 km. In this contribution, we estimate the cosmic-ray energy of the 14 individual events and find a mean energy of 2:9-1018 eV. By simulating the ANITA flight, we calculate its exposure for ultra-high energy cosmic rays (UHECRs) and we estimate for the first time the cosmic-ray flux derived only from radio observations.

Abstract:

From an elevation of ~38 km, the balloon-borne ANtarctic Impulsive Transient Antenna (ANITA) is designed to detect the up-coming radio frequency (RF) signal resulting from a sub-surface neutrino-nucleon collision. Although no neutrinos have been discovered thus far, ANITA is nevertheless the only experiment to self-trigger on radio frequency emissions from cosmic-ray induced atmospheric air showers. In the majority of those cases, down-coming RF signals are observed via their reflection from the Antarctic ice sheet and back up to the ANITA interferometer. Estimating the energy scale of the incident cosmic rays therefore requires an estimate of the fractional power reflected at the air-ice interface. Similarly, inferring the energy of neutrinos interacting in-ice from observations of the upwards-directed signal refracting out to ANITA also requires consideration of signal coherence across the interface. By comparing the direct Solar RF signal intensity measured with ANITA to the surface-reflected Solar signal intensity, as a function of incident elevation angle relative to the surface {\Theta}, we estimate the power reflection coefficients R({\Theta}). We find general consistency between our average measurements and the values of R({\Theta}) expected from the Fresnel equations, separately for horizontal- vs. vertical-polarizations.