LOPES: detecting radio emission from cosmic ray air showers

Abstract

Radio pulses emitted in the atmosphere during the air shower development of high-energy primary cosmic rays were measured during the late 1960ies in the frequency range from 2 MHz to 520 MHz. Mainly due to difficulties with radio interference these measurements ceased in the late 1970ies.LOFAR (Low Frequency Array) is a new digital radio interferometer under development. Using high bandwidth ADCs and fast data processing it will be able to filter out most of the interference. By storing the whole waveform information in digital form one can analyze transient events like air showers even after they have been recorded.To test this new technology and to demonstrate its ability to measure air showers a "LOFAR Prototype Station" (LOPES) is set up to operate in conjunction with an existing air shower array (KASCADE-Grande).The first phase consisting of 10 antennas is already running. It operates in the frequency range of 40 to 80 MHz, using simple short dipole antennas and direct 2nd Nyquist sampling of the incoming wave. It has proven to be able to do simple astronomical measurements, like imaging of a solar burst. It has also demonstrated how digital interference suppression and beamforming can overcome the problem of radio interference and pick out air shower events.

Radio emission from cosmic ray air showers: Simulation results and parametrization

“…On the experimental side, the LOPES project [6] is developing and testing the design of a LOFAR prototype station for the measurement of cosmic ray air showers. It will provide experimental data that should finally pin down the absolute strength as well as the polarization properties of the radio emission very soon.…”

Detection and imaging of atmospheric radio flashes from cosmic ray air showers

“…KASCADE provides coincidence triggers for LOPES and well-calibrated information about air shower properties. Experimental procedure and data reduction have been described elsewhere 17 and we give here only a brief summary in the Methods section. A related experiment is currently under way at the Nançay radio observatory 18 .…”

The KASCADE-Grande Experiment and the LOPES Project

“…The antennas operate in the frequency range of 40-80 MHz. A preliminary analysis of the first data has already been performed [16]. Fig.…”

“…Steps of the reconstruction of a strong air shower event[16] detected by LOPES. In the upper part the received powers (squares of the electric fields) of 8 antennas before beamforming are overlayed.…”