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The Pierre Auger observatory is presently being upgraded to enlarge its detection capabilities for ultra-high-energy cosmic rays. Part of this upgrade is a radio detector array, aimed to cover a surface area of 3000 km2 to measure the properties of the highestenergy cosmic rays. The plans for this radio upgrade are outlined. [ABSTRACT FROM AUTHOR]

Radio detection of extensive air showers is a flourish technique, attracting more and more interest to investigate the properties of high-energy cosmic rays. Past, present, and future developments are reviewed. [ABSTRACT FROM AUTHOR]

The Pierre Auger Observatory is presently being upgraded to enlarge its detection capabilities for ultra-high-energy cosmic rays. Part of this upgrade is a radio detector array, aimed to cover a surface area of 3000 km2 to measure the properties of the highest-energy cosmic rays. The plans for this radio upgrade are outlined [ABSTRACT FROM AUTHOR]

Status and perspectives of the radio detection of high-energy cosmic rays are discussed with emphasis on recent developments at the LOFAR radio telescope and the Pierre Auger Observatory. [ABSTRACT FROM AUTHOR]

High-energy cosmic rays, impinging on the atmosphere of the Earth initiate cascades of secondary particles, the extensive air showers. The electrons and positrons in the air shower emit electromagnetic radiation. This emission is detected with the LOFAR radio telescope in the frequency range from 30 to 240 MHz. The data are used to determine the properties of the incoming cosmic rays. The radio technique is now routinely used to measure the arrival direction, the energy, and the particle type (atomic mass) of cosmic rays in the energy range from 1017 to 1018 eV. This energy region is of particular astrophysical interest, since in this regime a transition from a Galactic to an extra-galactic origin of cosmic rays is expected. For illustration, the LOFAR results are used to set constraints on models to describe the origin of high-energy cosmic rays. [ABSTRACT FROM AUTHOR]

One of the main ways to use radio to detect Ultra High Energy Neutrinos and Cosmic Rays is the Lunar Askaryan technique, that uses the Moon as a target and searches for nanosecond pulses with large radio telescopes. To use low frequency aperture arrays, such as LOFAR and the SKA, pose new challenges and possibilities in detection techniques of short radio pulses and to measure the Total Electron Content (TEC). As a prepatory work, we have used other measurements that use similar techniques, or that can answer a specific question, with the LOFAR radio telescope. This contribution reports on our work on triggering on short radio signals, post-event imaging of radio signals from buffered data and methods to determine the TEC-value. [ABSTRACT FROM AUTHOR]

The refractive index of the atmosphere, which is n ∼ 1:0003 at sea level, varies with altitude and with local temperature, pressure and humidity. When performing radio measurements of air showers, natural variations in n will change the radio lateral intensity distribution, by changing the Cherenkov angle. Using CoREAS simulations, we have evaluated the systematic error on measurements of the shower maximum Xmax due to variations in n. It was found that a 10% increase in refractivity (n - 1) leads to an underestimation of Xmax between 8 and 22 g/cm2 for proton-induced showers at zenith angles from 15 to 45 degrees, respectively. [ABSTRACT FROM AUTHOR]

A simulation study of the energy released by extensive air showers in the form of MHz radiation is performed using the CoREAS simulation code. We develop an efficient method to extract this radiation energy from air-shower simulations. We determine the longitudinal profile of the radiation energy release and compare it to the longitudinal profile of the energy deposit by the electromagnetic component of the air shower. We find that the radiation energy corrected for the geometric dependence of the geomagnetic emission scales quadratically with the energy in the electromagnetic component of the air shower with a second order dependency on the atmospheric density at the position of the maximum of the shower development Xmax. In a measurement where Xmax is not accessible, this second order dependence can be approximated using the zenith angle of the incoming direction of the air shower with only a minor deterioration in accuracy. This method results in an intrinsic uncertainty of 4% with respect to the electromagnetic shower energy which is well below current experimental uncertainties. [ABSTRACT FROM AUTHOR]

In the dense core of LOFAR individual air showers are detected by hundreds of dipole antennas simultaneously. We reconstruct Xmax by using a hybrid technique that combines a two-dimensional fit of the radio profile to CoREAS simulations and a one-dimensional fit of the particle density distribution. For high-quality detections, the statistical uncertainty on Xmax is smaller than 20 g/cm2. We present results of cosmic-ray mass analysis in the energy regime of 1017 - 1017.5 eV. This range is of particular interest as it may harbor the transition from a Galactic to an extragalactic origin of cosmic rays. [ABSTRACT FROM AUTHOR]

The high number density of radio antennas at the LOFAR core in Northern Netherlands allows to detect radio signals emitted by cosmic ray induced air showers, and to characterize the geometry of the observed cascade in a detailed way. We present here a study of the radio frequency spectrum in the 30 - 80 MHz regime, and its correlation with some geometrical parameters of the extensive air shower. An important goal of this study is to find a correlation between the frequency spectrum and the primary particle type. Preliminary results on how the frequency spectrum changes as function of distance to the shower axis, and as function of primary particles mass composition are shown. The final aim of this study is to find a method to infer information of primary cosmic rays in an independent way from the well-established fluorescence and surface detector techniques, in view of affirming the radio detection technique as reliable method for the study of high energy cosmic rays. [ABSTRACT FROM AUTHOR]

The radio signals emitted by Extensive Air Showers have been successfully used for the last decade by LOFAR to reconstruct the properties of the primary cosmic rays. Since an effective real-time recognition system for the very short radio pulses is lacking, cosmic-ray acquisition is currently triggered by an external array of particle detector, called LORA, limiting the LOFAR collecting area to the area covered by LORA. A new algorithm for the real-time cosmic-ray detection has been developed for the LOFAR Low Band Antenna, which are sensitive between 10 and 90 MHz, and is here presented together with the latest results. [ABSTRACT FROM AUTHOR]

The spatial signal distribution of the radio frequency radiation from extensive air showers on the ground contains information on crucial cosmic-ray properties, such as energy and mass. A long-standing challenge to access this information experimentally with a sparse grid of antennas is an analytic modeling of the radio signal distribution, which will be addressed in this contribution. We present an analytic model based on the two physical processes generating radio emission in air showers: the geomagnetic and the charge-excess emission. Our study is based on full Monte-Carlo simulations with the CoREAS code. Besides an improved theoretical understanding of radio emission, our model describes the radio signal distribution with unprecedented precision. Our model explicitly includes polarization information, which basically doubles the information that is used from a single radio station. The model depends only on the definition of the shower axis and on the parameters energy and distance to the emission region, where the distance to the emission region has a direct relation to the cosmic-ray mass. The model describes the true signal distribution precisely such that the model uncertainties are negligible compared to typical experimental uncertainties. [ABSTRACT FROM AUTHOR]

The LOw Frequency ARay (LOFAR) is a multi-purpose radio antenna array aimed to detect radio signals in the frequency range 10 - 240 MHz, covering a largesurface in Northern Europe with a higher density in the Netherlands. Analytical calculations and simulation studies performed in the 2000s indicate a dependence of the radio frequency spectrum on cosmic-ray characteristics. The high number density of radio antennas at the LOFAR core allows to characterise the observed cascade in a detailed way. The radio signal emitted by air showers in the atmosphere has been studied accurately in the 30 - 80 MHz frequency range. The analysis has been conducted on simulated eventsand on real data detected by LOFAR since 2011. The final aim of this study is to find an independent method to infer information of primary cosmic rays for improving the reconstruction of primary particle parameters. Results show a strong dependence of the frequency spectrum on the distance to the shower axis for both real data and simulations. Furthermore, results show that this method is very sensitive to the precision in reconstructing the position of the shower axis at ground, and to different antenna calibration procedures. A correlation between the frequency spectrum and geometrical distance to the shower maximum development Xmax has also been investigated. [ABSTRACT FROM AUTHOR]

Ultra-high-energy neutrinos and cosmic rays produce short radio flashes through the Askaryan effect when they impact on the Moon. Earthbound radio telescopes can search the Lunar surface for these signals. A new generation of lowfrequency, digital radio arrays, spearheaded by LOFAR, will allow for searches with unprecedented sensitivity. In the first stage of the NuMoon project, low-frequency observations were carried out with the Westerbork Synthesis Radio Telescope, leading to the most stringent limit on the cosmic neutrino flux above 1023 eV. With LOFAR we will be able to reach a sensitivity of over an order of magnitude better and to decrease the threshold energy. [ABSTRACT FROM AUTHOR]

LOFAR (the Low Frequency Array) is the largest radio telescope in the world for observing low frequency radio emission from 10 to 240 MHz. In addition to its use as an interferometric array, LOFAR is now routinely used to detect cosmic ray induced air showers by their radio emission. The LOFAR core in the Netherlands has a higher density of antennas than any dedicated cosmic ray experiment in radio. On an area of 12 km2 more than 2300 antennas are installed. They measure the radio emission from air showers with unprecedented precision and, therefore, give the perfect opportunity to disentangle the physical processes which cause the radio emission in air showers. In parallel to ongoing astronomical observations LOFAR is triggered by an array of particle detectors to record time-series containing cosmic-ray pulses. Cosmic rays have been measured with LOFAR since June 2011. We present the results of the first year of data. [ABSTRACT FROM AUTHOR]

Recent results on the composition of cosmic rays in the energy region from about 1014 to 1018 eV are reviewed. [ABSTRACT FROM AUTHOR]

The article gives an overview on early cosmic-ray work, published in German in the period from around 1910 to about 1940. [ABSTRACT FROM AUTHOR]