arXiv subjects

Tim Huege

Publications and source records attributed to Tim Huege.

99 records · Page 6Linked to original sources

arXiv2005

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

We have developed a sophisticated model of the radio emission from extensive air showers in the scheme of coherent geosynchrotron radiation, providing a theoretical foundation for the interpretation of experimental data from current and future experiments. Having verified the model through comparison of analytic calculations, Monte Carlo simulations and historical experimental data, we now present the results of extensive simulations performed with our Monte Carlo code. Important results are the absence of significant asymmetries in the total field strength emission pattern, the spectral dependence of the radiation, the polarization characteristics of the emission (allowing an unambiguous test of the geomagnetic emission mechanism), and the dependence of the radio emission on important air shower and observer parameters such as the shower zenith angle, the primary particle energy, the depth of the shower maximum and the observer position. An analytic parametrization incorporating the aforementioned dependences summarizes our results in a particularly useful way.

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arXiv2005

Monte Carlo simulations of radio emission from cosmic ray air showers

As a basis for the interpretation of data gathered by LOPES and other experiments, we have carried out Monte Carlo simulations of geosynchrotron radio emission from cosmic ray air showers. The simulations, having been verified carefully with analytical calculations, reveal a wealth of information on the characteristics of the radio signal and their dependence on specific air shower parameters. In this article, we review the spatial characteristics of the radio emission, its predicted frequency spectrum and its dependence on important air shower parameters such as the shower zenith angle, the primary particle energy and the depth of the shower maximum, which can in turn be related to the nature of the primary particle.

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arXiv2005

Simulations and parametrisation of radio emission from cosmic ray air showers

Cosmic ray air showers are known to emit pulsed radio emission at frequencies around a few tens of MHz. Accompanying the experimental efforts of the LOPES project, situated at the KASCADE-Grande site of the Forschungszentrum Karlsruhe, we have modeled the underlying emission mechanism in the scheme of coherent geosynchrotron radiation from electron-positron pairs deflected in the earth's magnetic field. As a follow-up to our earlier analytical calculations, we have developed a Monte Carlo simulation based on analytic parametrisations of air shower properties, including longitudinal and lateral particle distributions, particle energy and track-length distributions, and the longitudinal shower development as a whole. Here we present detailed simulation results. Important findings are the absence of significant asymmetries in the total field strength emission pattern in spite of the asymmetry introduced by the geomagnetic field, the polarisation characteristics of the geosynchrotron emission, allowing an unambiguous test of the geomagnetic emission mechanism, and the dependence of the radio emission on important shower parameters such as the shower zenith angle, the primary particle energy and the depth of the shower maximum. As a particularly useful result, these dependences have been summarized in a simple parametrisation formula, providing a solid basis for the interpretation of experimental data gathered with current and future experiments.

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arXiv2005

Fluctuations in the EAS radio signal derived with improved Monte Carlo simulations based on CORSIKA

Cosmic ray air showers are known to emit pulsed radio emission which can be understood as coherent geosynchrotron radiation arising from the deflection of electron-positron pairs in the earth's magnetic field. Here, we present simulations carried out with an improved version of our Monte Carlo code for the calculation of geosynchrotron radiation. Replacing the formerly analytically parametrised longitudinal air shower development with CORSIKA-generated longitudinal profiles, we study the radio flux variations arising from inherent fluctuations between individual air showers. Additionally, we quantify the dependence of the radio emission on the nature of the primary particle by comparing the emission generated by proton- and iron-induced showers. This is only the first step in the incorporation of a more realistic air shower model into our Monte Carlo code. The inclusion of highly realistic CORSIKA-based particle energy, momentum and spatial distributions together with an analytical treatment of ionisation losses will soon allow simulations of the radio emission with unprecedented detail. This is especially important to assess the emission strengths at large radial distances, needed for event-to-event comparisons of the radio signals measured by LOPES in conjunction with KASCADE-Grande and for considerations regarding large arrays of radio antennas intended to measure the radio emission from ultra-high energy cosmic rays, as with LOFAR or in the Pierre Auger Observatory.

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arXiv2004

Simulations of Radio Emission from Cosmic Ray Air Showers

Radio emission from cosmic ray air showers has the potential to become an additional, cost-effective observing technique for cosmic ray research, being largely complementary to the well-established particle detector and air fluorescence techniques. We present Monte Carlo simulatios of radio emission from extensive air showers in the scheme of coherent geosynchrotron radiation from electron-positron pairs gyrating in the earth's magnetic field. Preliminary results of our simulations are the predicted frequency, primary particle energy, shower zenith angle, shower azimuth angle and polarization dependence of the radio emission. These properties can be directly related to data measured by LOPES and other experiments.

astro-ph↗

arXiv2004

Radio emission from cosmic ray air showers: Monte Carlo simulations

We present time-domain Monte Carlo simulations of radio emission from cosmic ray air showers in the scheme of coherent geosynchrotron radiation. Our model takes into account the important air shower characteristics such as the lateral and longitudinal particle distributions, the particle track length and energy distributions, a realistic magnetic field geometry and the shower evolution as a whole. The Monte Carlo approach allows us to retain the full polarisation information and to carry out the calculations without the need for any far-field approximations. We demonstrate the strategies developed to tackle the computational effort associated with the simulation of a huge number of particles for a great number of observer bins and illustrate the robustness and accuracy of these techniques. We predict the emission pattern, the radial and the spectral dependence of the radiation from a prototypical 10^17 eV vertical air shower and find good agreement with our analytical results (Huege & Falcke 2003) and the available historical data. Track-length effects in combination with magnetic field effects surprisingly wash out any significant asymmetry in the total field strength emission pattern in spite of the magnetic field geometry. While statistics of total field strengths alone can therefore not prove the geomagnetic origin, the predicted high degree of polarisation in the direction perpendicular to the shower and magnetic field axes allows a direct test of the geomagnetic emission mechanism with polarisation-sensitive experiments such as LOPES. Our code provides a robust, yet flexible basis for detailed studies of the dependence of the radio emission on specific shower parameters and for the inclusion of additional radiation mechanism in the future.

astro-ph↗

arXiv2003

Radio Emission from Cosmic Ray Air Showers: Coherent Geosynchrotron Radiation

Cosmic ray air showers have been known for over 30 years to emit pulsed radio emission in the frequency range from a few to a few hundred MHz, an effect that offers great opportunities for the study of extensive air showers with upcoming fully digital "software radio telescopes" such as LOFAR and the enhancement of particle detector arrays such as KASCADE Grande or the Pierre Auger Observatory. However, there are still a lot of open questions regarding the strength of the emission as well as the underlying emission mechanism. Accompanying the development of a LOFAR prototype station dedicated to the observation of radio emission from extensive air showers, LOPES, we therefore take a new approach to modeling the emission process, interpreting it as "coherent geosynchrotron emission" from electron-positron pairs gyrating in the earth's magnetic field. We develop our model in a step-by-step procedure incorporating increasingly realistic shower geometries in order to disentangle the coherence effects arising from the different scales present in the air shower structure and assess their influence on the spectrum and radial dependence of the emitted radiation. We infer that the air shower "pancake" thickness directly limits the frequency range of the emitted radiation, while the radial dependence of the emission is mainly governed by the intrinsic beaming cone of the synchrotron radiation and the superposition of the emission over the air shower evolution as a whole. Our model succeeds in reproducing the qualitative trends in the emission spectrum and radial dependence that were observed in the past, and is consistent with the absolute level of the emission within the relatively large systematic errors in the experimental data.

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arXiv2003

Radio Emission From EAS - Coherent Geosynchrotron Radiation

Extensive air showers (EAS) have been known for over 30 years to emit pulses of radio emission at frequencies from a few to a few hundred MHz, an effect that offers great opportunities for the study of EAS with the next generation of "software radio interferometers" such as LOFAR and LOPES. The details of the emission mechanism, however, remain rather uncertain to date. Following past suggestions that the bulk of the emission is of geomagnetic origin, we model the radio pulses as "coherent geosynchrotron radiation" arising from the deflection of electrons and positrons in the earth's magnetic field. We analytically develop our model in a step-by-step procedure to disentangle the coherence effects arising from different scales present in the shower structure and infer which shower characteristics govern the frequency spectrum and radial dependence of the emission. The effect is unavoidable and our predictions are in good agreement with the available experimental data within their large margins of error.

astro-ph↗

arXiv2002

Radio-Emission from Cosmic Ray Air-Showers - A Theoretical Perspective for LOPES

High-energy cosmic ray air-showers have been known for over 30 years to emit strong radio pulses in the regime between a few and several 100 MHz (Allan 1971). To date, however, a thorough analysis of the emission mechanisms has not yet been conducted. Adopting a simplified shower geometry and electron-positron energy distribution, we calculate theoretical pulse spectra in the scheme of synchrotron emission from highly relativistic electron-positron pairs gyrating in the Earth's magnetic field. These calculations will play an important role for the calibration of observational data of radio-emission from cosmic ray air-showers acquired with LOPES and later LOFAR and SKA.

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