Washington Rodrigues de Carvalho

Coherent Radiation from Extensive Air Showers in the Ultra-High Frequency Band

Using detailed Monte Carlo simulations we have characterized the features of the radio emission of inclined air showers in the ultrahigh frequency band (300 MHz\char21{}3 GHz). The Fourier spectrum of the radiation is shown to have a sizable intensity well into the GHz frequency range. The emission is mainly due to transverse currents induced by the geomagnetic field and the excess charge produced by the Askaryan effect. At these frequencies only a significantly reduced volume of the shower around the axis contributes coherently to the signal observed on the ground. The size of the coherently emitting volume depends on frequency, shower geometry and observer position, and is interpreted in terms of the relative time delays at observation dominated by the curvature of the shower front. At ground level, the maximum emission at high frequencies is concentrated in an elliptical ringlike region around the intersection of a Cherenkov cone with its vertex at shower maximum and the ground. The frequency spectrum of inclined showers when observed at positions that view shower maximum in the Cherenkov direction, is shown to be in broad agreement with the pulses detected by the Antarctic Impulsive Transient Antenna experiment, making the interpretation that they are due to ultrahigh energy cosmic ray atmospheric showers consistent with our simulations. These results are also of great importance for experiments aiming to detect molecular bremsstrahlung radiation in the GHz range as they present an important background for its detection.

A Search for Microwave Emission From Ultra-High Energy Cosmic Rays

We present a search for microwave emission from air showers induced by ultrahigh energy cosmic rays with the microwave detection of air showers experiment. No events were found, ruling out a wide range of power flux and coherence of the putative emission, including those suggested by recent laboratory measurements.

Radio pulses from ultra-high energy atmospheric showers as the superposition of Askaryan and geomagnetic mechanisms

Abstract Radio emission in atmospheric showers is currently interpreted in terms of radiation due to the deviation of the charged particles in the magnetic field of the Earth and to the charge excess (Askaryan effect). Each of these mechanisms has a distinctive polarization. The complex signal patterns can be qualitatively explained as the interference (superposition) of the fields induced by each mechanism. In this work we explicitly and quantitatively test a simple phenomenological model based on this idea. The model is constructed by isolating each of the two components at the simulation level and by making use of approximate symmetries for each of the contributions separately. The results of the model are then checked against full ZHAireS Monte Carlo simulations of the electric field calculated from first principles. We show that the simple model describes radio emission at a few percent level in a wide range of shower-observer geometries and on a shower-by-shower basis. As a consequence, this approach provides a simple method to reduce the computing time needed to accurately predict the electric field of radio pulses emitted from air showers, with many practical applications in experimental situations of interest.

Calculations of electric fields for radio detection of ultrahigh energy particles

The detection of electromagnetic pulses from high energy showers is used as a means to search for Ultra-High Energy cosmic ray and neutrino interactions. An approximate formula has been obtained to numerically evaluate the radio pulse emitted by a charged particle that instantaneously accelerates, moves at constant speed along a straight track and halts again instantaneously. The approximate solution is applied to the particle track after dividing it in smaller subintervals. The resulting algorithm (often referred to as the ZHS algorithm) is also the basis for most of the simulations of the electric field produced in high energy showers in dense media. In this work, the electromagnetic pulses as predicted with the ZHS algorithm are compared to those obtained with an exact solution of the electric field produced by a charged particle track. The precise conditions that must apply for the algorithm to be valid are discussed and its accuracy is addressed. This comparison is also made for electromagnetic showers in dense media. The ZHS algorithm is shown to describe Cherenkov radiation and to be valid for most situations of interest concerning detectors searching for Ultra-High Energy neutrinos. The results of this work are also relevant for the simulation of pulses emitted from air showers.

Simulations of reflected radio signals from cosmic ray induced air showers

Abstract We present the calculation of coherent radio pulses emitted by extensive air showers induced by ultra-high energy cosmic rays accounting for reflection on the Earth’s surface. Results have been obtained with a simulation program that calculates the contributions from shower particles after reflection at a surface plane. The properties of the radiation are discussed in detail emphasizing the effects of reflection. The shape of the frequency spectrum is shown to be closely related to the angle of the observer with respect to shower axis, becoming hardest in the Cherenkov direction. The intensity of the flux at a fixed observation angle is shown to scale with the square of the primary particle energy to very good accuracy indicating the coherent aspect of the emission. The simulation methods of this paper provide the foundations for energy reconstruction of experiments looking at the Earth from balloons and satellites. They can also be used in dedicated studies of existing and future experimental proposals.

Ultra high frequency geomagnetic radiation from extensive air showers

Using the ZHAireS Monte Carlo code, we show that the Fourier-spectrum of the radio emission of inclined air showers can have a sizable intensity up to the GHz frequency range. At these frequencies only a significantly reduced volume of the shower around the axis contributes coherently to the signal observed on the ground, which is mainly due to the geomagnetic and charge excess mechanisms. At ground level, the maximum emission at high frequencies is concentrated in a ring-like elliptical region defined by the intersection with the ground of a Cherenkov cone with its vertex at shower maximum. The frequency-spectrum of inclined showers, when observed at positions close to the ring-like maximum emission region, is in broad agreement with the pulses detected by the ANITA experiment, making the interpretation that they are due to ultrahigh energy cosmic ray atmospheric showers consistent with our simulations. These results are also relevant for ground-based radio experiments aiming at detecting molecular brems...

Upward-Pointing Cosmic-Ray-like Events Observed with ANITA

These proceedings address a recent publication by the ANITA collaboration of four upward- pointing cosmic-ray-like events observed in the first flight of ANITA. Three of these events were consistent with stratospheric cosmic-ray air showers where the axis of propagation does not inter- sect the surface of the Earth. The fourth event was consistent with a primary particle that emerges from the surface of the ice suggesting a possible {\tau}-lepton decay as the origin of this event. These proceedings follow-up on the modeling and testing of the hypothesis that this event was of {\tau} neutrino origin.

The Giant Radio Array for Neutrino Detection (GRAND) : Present and Perspectives

The Giant Radio Array for Neutrino Detection (GRAND) aims at detecting ultra-high energy extraterrestrial neutrinos via the extensive air showers induced by the decay of tau leptons created in the interaction of neutrinos under the Earths surface. Consisting of an array of

The GRANDproto35 experiment

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The MIDAS experiment: A prototype for the microwave emission of Ultra-High Energy Cosmic Rays

radio antennas deployed over