Polarized radio emission from extensive air showers measured with LOFAR

Understand

We present LOFAR measurements of radio emission from extensive air showers.

• We find that this emission is strongly polarized, with a median degree of polarization of nearly $99\%$, and that the angle between the polarization direction of the electric field and the Lorentz force acting on the particles, depends on the observer location in the shower plane.
• This can be understood as a superposition of the radially polarized charge-excess emission mechanism, first proposed by Askaryan and the geomagnetic emission mechanism proposed by Kahn and Lerche.
• We calculate the relative strengths of both contributions, as quantified by the charge-excess fraction, for $163$ individual air showers.