G. W. Kant

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

The nature of ultrahigh-energy cosmic rays (UHECRs) at energies >1020 eV remains a mystery. They are likely to be of extragalactic origin, but should be absorbed within ∼50 Mpc through interactions with the cosmic microwave background. As there are no sufficiently powerful accelerators within this distance from the Galaxy, explanations for UHECRs range from unusual astrophysical sources to exotic string physics. Also unclear is whether UHECRs consist of protons, heavy nuclei, neutrinos or γ-rays. To resolve these questions, larger detectors with higher duty cycles and which combine multiple detection techniques are needed. Radio emission from UHECRs, on the other hand, is unaffected by attenuation, has a high duty cycle, gives calorimetric measurements and provides high directional accuracy. Here we report the detection of radio flashes from cosmic-ray air showers using low-cost digital radio receivers. We show that the radiation can be understood in terms of the geosynchrotron effect. Our results show that it should be possible to determine the nature and composition of UHECRs with combined radio and particle detectors, and to detect the ultrahigh-energy neutrinos expected from flavour mixing.

Extending the Field of View With Phased Array Techniques: Results of European SKA Research

The radio frequency window of the square kilometre array is planned to cover the wavelength regime from centimeters up to a few meters. For this range to be optimally covered, different antenna concepts are considered. At the lowest frequency range, up to a few gigahertz, it is expected that multibeam techniques will be used, increasing the effective field-of-view to a level that allows very efficient detailed and sensitive exploration of the complete sky. Although sparse narrow-band phased arrays are as old as radio astronomy, multioctave sparse and dense arrays now considered for the SKA require new low-noise design, signal processing, and calibration techniques. The successful implementation of these new array techniques has already been introduced for the use of phased array feeds upgrading existing telescopes: enhancing aperture efficiency as well as effective field-of-view. Especially the development of low-cost array antenna design will allow a cost-effective large-scale implementation for the SKA. This paper addresses these new capabilities, emphasizing the R&D work done in Europe and aims to provide insight into the status of enabling technologies and technical research on polarization, calibration, and side-lobe control that will unleash the potential of phased arrays for future growth of radio astronomy synthesis arrays.

Low cost low noise phased-array feeding systems for SKA pathfinders

Developments in radio astronomy instrumentation drive the need for lower cost front-ends due to the large number of antennas and low noise amplifiers needed. This paper describes cost reduction techniques for the realization of antennas and low noise amplifiers in combination with a noise budget calculation for array systems in the absence of cryogenic cooling.

Beamforming techniques for large-N aperture arrays

Beamforming is central to the processing function of all phased arrays and becomes particularly challenging with a large number of antenna element (e.g. >100,000). The ability to beamform efficiently with reasonable power requirements is discussed in this paper. Whilst the most appropriate beamforming technology will change over time due to semiconductor and processing developments, we present a hierarchical structure which is technology agnostic and describe both Radio-Frequency (RF) and digital hierarchical beamforming approaches. We present implementations of both RF and digital beamforming systems on two antenna array demonstrators, namely the Electronic Multi Beam Radio Astronomy ConcEpt (EMBRACE) and the dualpolarisation all-digital array (2-PAD). This paper will compare and contrast both digital and analogue implementations without considering the deep system design of these arrays.

The KASCADE-Grande experiment and the LOPES project

KASCADE-Grande is the extension of the multi-detector setup KASCADE to cover a primary cosmic ray energy range from 100 TeV to 1 EeV. The enlarged EAS experiment provides comprehensive observations of cosmic rays in the energy region around the knee. Grande is an array of 700 x 700 sqm equipped with 37 plastic scintillator stations sensitive to measure energy deposits and arrival times of air shower particles. LOPES is a small radio antenna array to operate in conjunction with KASCADE-Grande in order to calibrate the radio emission from cosmic ray air showers. Status and capabilities of the KASCADE-Grande experiment and the LOPES project are presented.

Results from the KASCADE, KASCADE-Grande, and LOPES experiments

The origin of high-energy cosmic rays in the energy range from 1014 to 1018 eV is explored with the KASCADE and KASCADE-Grande experiments. Radio signals from air showers are measured with the LOPES experiment. An overview on results is given.

EMBRACE: First experimental Results with the Initial 10% of a 10,000 Element Phased Array Radio Telescope

The Electronic Multi-beam Radio Astronomy Concept (EMBRACE) is the first full-scale prototype of an SKA phased array station. This single polarization demonstrator operates between 500 and 1500 MHz. The station that is currently being built at the site of the Westerbork Synthesis Radio Telescope, will ultimately consist of 144 tiles with 72 single polarization Vivaldi antennas each, giving a total of ∼ 104 elements. The station is equipped with a LOFAR station backend with 192 input channels, which can be exploited for real-time digital beam forming in 248 frequency channels of 195 kHz (∼ 48 MHz total bandwidth) and correlation in a single 195 kHz frequency channel. In this paper we present the results from a number of system validation measurements and the first fringes on an astronomical source, the sun. These initial measurements indicate a system temperature between 103 K and 117 K. These results corroborate the feasibility and applicability of phased array technology at frequencies below 1500 MHz. They also provide valuable insights for the aperture array verification program, the next step in aperture array development towards the SKA.

Radio emission of highly inclined cosmic ray air showers measured with LOPES - possibility for neutrino detection

LOPES-10 (the first phase of LOPES, consisting of 10 antennas) detected a significant number of cosmic ray air showers with a zenith angle larger than 50

Absolute calibration of the LOPES antenna system

^{\circ}

KASCADE extensive air shower experiment

, and many of these have very high radio field strengths. The most inclined event that has been detected with LOPES-10 has a zenith angle of almost 80