Calculations of radio pulses from High Energy Showers

In this article we review the progress made in understanding the main characteristics of coherent \v{C}erenkov radiation induced by high energy showers in dense media. A specific code developed for this purpose is described because it took a significant part in this process. Subsequent approximations developed for the calculation of radio pulses from EeV showers are reviewed. Emphasis is given to the relation between the shower characteristics and different features of the corresponding radio emission.Comment: Latex file, aipproc.sty and epsfig.sty, 11 pages, 6 figures, talk given at the 1st International Workshop on Radio Detection of High Energy Particles (RADHEP-2000), UCLA, November 200

Density and magnetic intensity dependence of radio pulses induced by energetic air showers

We have studied the effect of changing the density and magnetic field strength in the coherent pulses that are emitted as energetic showers develop in the atmosphere. For this purpose we have developed an extension of ZHS, a program to calculate coherent radio pulses from electromagnetic showers in homogeneous media, to account for the Lorentz force due to a magnetic field. This makes it possible to perform quite realistic simulations of radio pulses from air showers in a medium similar to the atmosphere but without variations of density with altitude. The effects of independently changing the density, the refractive index and the magnetic field strength are studied in the frequency domain for observers in the Cherenkov direction at far distances from the shower. This approach is particularly enlightening providing an explanation of the spectral behavior of the induced electric field in terms of shower development parameters. More importantly, it clearly displays the complex scaling properties of the pulses as density and magnetic field intensity are varied. The usually assumed linear behavior of electric field amplitude with magnetic field intensity is shown to hold up to a given magnetic field strength at which the extra time delays due to the deflection in the magnetic field break it. Scaling properties of the pulses are obtained as the density of air decreases relative to sea level. A remarkably accurate scaling law is obtained that relates the spectra of pulses obtained when reducing the density and increasing the magnetic field.Comment: 27 pages, 14 figure

Monte Carlo simulations of radio pulses in atmospheric showers using ZHAireS

We present predictions for the radio pulses emitted by extensive air showers using ZHAireS, an AIRES-based Monte Carlo code that takes into account the full complexity of ultra-high energy cosmic-ray induced shower development in the atmosphere, and allows the calculation of the electric field in both the time and frequency domains. We do not presuppose any emission mechanism, but our results are compatible with a superposition of geomagnetic and charge excess radio emission effects. We investigate the polarization of the electric field as well as the effects of the refractive index n and shower geometry on the radio pulses. We show that geometry, coupled to the relativistic effects that appear when using a realistic n>1, play a prominent role on the radio emission of air showers.Comment: Replaced with version published in Astroparticle Physic

Measurement of the cosmic ray flux with the ANITA experiment

The ANITA experiment consists on an aerostatic balloon flying over Antarctica and carrying a payload with antennas. Although ANITA was designed to detect the electric field of netrino-induced showers in the ice cap, it has also detected 16 radio pulses coming from extensive air showers, and the ANITA collaboration has used these data to produce the first cosmic ray flux measurement obtained by employing radio as a stand-alone technique. We review the experimental results and its interpretation. We also focus on the simulations and the method used for obtaining the cosmic ray flux