Probing the radio emission from air showers with polarization measurements

Abstract

The emission of radio waves from air showers has been attributed to the so-called geomagnetic emission process. At frequencies around 50 MHz this process leads to coherent radiation which can be observed with rather simple setups. The direction of the electric field induced by this emission process depends only on the local magnetic field vector and on the incoming direction of the air shower. We report on measurements of the electric field vector where, in addition to this geomagnetic component, another component has been observed that cannot be described by the geomagnetic emission process. The data provide strong evidence\ud hat the other electric field component is polarized radially with respect to he shower axis, in agreement\ud with predictions made by Askaryan who described radio emission from particle showers due to a negative\ud charge excess in the front of the shower. Our results are compared to calculations which include the\ud radiation mechanism induced by this charge-excess proces

Method for high precision reconstruction of air showerXmaxusing two-dimensional radio intensity profiles

“…Proof for a contribution of charge excess was found by CODALEMA [32] and later by polarization studies of AERA [25] and LOFAR [26]. CROME [33] and ANITA [34] detected GHz emission at the Cherenkov angle, which can be interpreted as relativistic compression of the airshower radio emission.…”

“…The relative contribution of charge excess to the total emission depends on the geometry (angle to the geomagnetic field, zenith angle, observer position, etc.) and has typical values of 5%-20% of the total pulse amplitude [24][25][26].…”

Laboratory tests of two-dimensional wavelet trigger in radio detection of cosmic rays

“…3D-plots generated by MAXIMA for arbitrarily assumed frequency spectrum of artificially generated pulse by iFFT with 4 peaks above the threshold (corresponding to 17.12, 40.9, 65.2 and 90.7 MHz, respectively, left graph) and for with only 2 peaks (corresponding to 40.9 and 65.2 MHz, respectively, right graph). The axis x corresponds to the frequency range from 0 to 100 MHz, the axis y denotes time evolution, the axis z is in arbitrarily units corresponding to (6). signal power simultaneously for time and frequency.…”

The Energy Content of Extensive Air Showers in the Radio Frequency Range of 30-80 MHz

“…The second component is polarized radially with respect to the axis of the air shower and results from the negative charge excess in the shower front [9,10,11,12]. Its relative strength is on average 14% at the Auger site for an air shower arriving perpendicular to the geomagnetic field [13]. The constructive and destructive interference of the two emission processes lead to a radial asymmetry of the lateral signal distribution function (LDF) [14,15,16] that can be modeled with a two-dimensional LDF [17,18].…”