arXiv subjects

A. Horneffer

Publications and source records attributed to A. Horneffer.

66 records · Page 4Linked to original sources

arXiv2012

Experimental evidence for the sensitivity of the air-shower radio signal to the longitudinal shower development

We observe a correlation between the slope of radio lateral distributions, and the mean muon pseudorapidity of 59 individual cosmic-ray-air-shower events. The radio lateral distributions are measured with LOPES, a digital radio interferometer co-located with the multi-detector-air-shower array KASCADE-Grande, which includes a muon-tracking detector. The result proves experimentally that radio measurements are sensitive to the longitudinal development of cosmic-ray air-showers. This is one of the main prerequisites for using radio arrays for ultra-high-energy particle physics and astrophysics.

astro-ph.IM↗

arXiv2011

Probing the Magnetic Fields of Nearby Spiral Galaxies at Low Frequencies with LOFAR

While the Low Frequency Array (LOFAR) is still in its commissioning phase, early science results are starting to emerge. Two nearby galaxies, M51 and NGC4631, have been observed as part of the Magnetism Key Science Project's (MKSP) effort to increase our understanding of the nature of weak magnetic fields in galaxies. LOFAR and the complexity of its calibration as well as the aims and goals of the MKSP are presented.

astro-ph.CO↗

arXiv2011

LOFAR: Detecting Cosmic Rays with a Radio Telescope

LOFAR (the Low Frequency Array), a distributed digital radio telescope with stations in the Netherlands, Germany, France, Sweden, and the United Kingdom, is designed to enable full-sky monitoring of transient radio sources. These capabilities are ideal for the detection of broadband radio pulses generated in cosmic ray air showers. The core of LOFAR consists of 24 stations within 4 square kilometers, and each station contains 96 low-band antennas and 48 high-band antennas. This dense instrumentation will allow detailed studies of the lateral distribution of the radio signal in a frequency range of 10-250 MHz. Such studies are key to understanding the various radio emission mechanisms within the air shower, as well as for determining the potential of the radio technique for primary particle identification. We present the status of the LOFAR cosmic ray program, including the station design and hardware, the triggering and filtering schemes, and our initial observations of cosmic-ray-induced radio pulses.

astro-ph.HE↗

arXiv2011

Observing pulsars and fast transients with LOFAR

Low frequency radio waves, while challenging to observe, are a rich source of information about pulsars. The LOw Frequency ARray (LOFAR) is a new radio interferometer operating in the lowest 4 octaves of the ionospheric "radio window": 10-240MHz, that will greatly facilitate observing pulsars at low radio frequencies. Through the huge collecting area, long baselines, and flexible digital hardware, it is expected that LOFAR will revolutionize radio astronomy at the lowest frequencies visible from Earth. LOFAR is a next-generation radio telescope and a pathfinder to the Square Kilometre Array (SKA), in that it incorporates advanced multi-beaming techniques between thousands of individual elements. We discuss the motivation for low-frequency pulsar observations in general and the potential of LOFAR in addressing these science goals. We present LOFAR as it is designed to perform high-time-resolution observations of pulsars and other fast transients, and outline the various relevant observing modes and data reduction pipelines that are already or will soon be implemented to facilitate these observations. A number of results obtained from commissioning observations are presented to demonstrate the exciting potential of the telescope. This paper outlines the case for low frequency pulsar observations and is also intended to serve as a reference for upcoming pulsar/fast transient science papers with LOFAR.

astro-ph.IM↗

arXiv2011

An air shower array for LOFAR: LORA

LOFAR is a new form of radio telescope which can detect radio emission from air showers induced by very high-energy cosmic rays. It can also look for radio emission from particle cascades on the Moon induced by ultra high-energy cosmic rays or neutrinos. To complement the radio detection, we are setting up a small particle detector array LORA (LOfar Radboud Air shower array) within an area of $\sim 300$ m diameter in the LOFAR core. It will help in triggering and confirming the radio detection of air showers with the LOFAR antennas. In this paper, we present a short overview about LORA and discuss its current status.

astro-ph.IM↗

arXiv2010

On noise treatment in radio measurements of cosmic ray air showers

Precise measurements of the radio emission by cosmic ray air showers require an adequate treatment of noise. Unlike to usual experiments in particle physics, where noise always adds to the signal, radio noise can in principle decrease or increase the signal if it interferes by chance destructively or constructively. Consequently, noise cannot simply be subtracted from the signal, and its influence on amplitude and time measurement of radio pulses must be studied with care. First, noise has to be determined consistently with the definition of the radio signal which typically is the maximum field strength of the radio pulse. Second, the average impact of noise on radio pulse measurements at individual antennas is studied for LOPES. It is shown that a correct treatment of noise is especially important at low signal-to-noise ratios: noise can be the dominant source of uncertainty for pulse height and time measurements, and it can systematically flatten the slope of lateral distributions. The presented method can also be transfered to other experiments in radio and acoustic detection of cosmic rays and neutrinos.

astro-ph.IM↗

arXiv2010

New method for the time calibration of an interferometric radio antenna array

Digital radio antenna arrays, like LOPES (LOFAR PrototypE Station), detect high-energy cosmic rays via the radio emission from atmospheric extensive air showers. LOPES is an array of dipole antennas placed within and triggered by the KASCADE-Grande experiment on site of the Karlsruhe Institute of Technology, Germany. The antennas are digitally combined to build a radio interferometer by forming a beam into the air shower arrival direction which allows measurements even at low signal-to-noise ratios in individual antennas. This technique requires a precise time calibration. A combination of several calibration steps is used to achieve the necessary timing accuracy of about 1 ns. The group delays of the setup are measured, the frequency dependence of these delays (dispersion) is corrected in the subsequent data analysis, and variations of the delays with time are monitored. We use a transmitting reference antenna, a beacon, which continuously emits sine waves at known frequencies. Variations of the relative delays between the antennas can be detected and corrected for at each recorded event by measuring the phases at the beacon frequencies.

astro-ph.IM↗

arXiv2009

Lateral Distribution of the Radio Signal in Extensive Air Showers Measured with LOPES

The antenna array LOPES is set up at the location of the KASCADE-Grande extensive air shower experiment in Karlsruhe, Germany and aims to measure and investigate radio pulses from Extensive Air Showers. The coincident measurements allow us to reconstruct the electric field strength at observation level in dependence of general EAS parameters. In the present work, the lateral distribution of the radio signal in air showers is studied in detail. It is found that the lateral distributions of the electric field strengths in individual EAS can be described by an exponential function. For about 20% of the events a flattening towards the shower axis is observed, preferentially for showers with large inclination angle. The estimated scale parameters R0 describing the slope of the lateral profiles range between 100 and 200 m. No evidence for a direct correlation of R0 with shower parameters like azimuth angle, geomagnetic angle, or primary energy can be found. This indicates that the lateral profile is an intrinsic property of the radio emission during the shower development which makes the radio detection technique suitable for large scale applications.

astro-ph.HE↗

arXiv2009

Air Shower Measurements with LOFAR

Air showers from cosmic rays emit short, intense radio pulses. LOFAR is a new radio telescope, that is being built in the Netherlands and Europe. Designed primarily as a radio interferometer, the core of LOFAR will have a high density of radio antennas, which will be extremely well calibrated. This makes LOFAR a unique tool for the study of the radio properties of single air showers. Triggering on the radio emission from air showers means detecting a short radio pulse and discriminating real events from radio interference. At LOFAR we plan to search for pulses in the digital data stream - either from single antennas or from already beam-formed data - and calculate several parameters characterizing the pulse shape to pick out real events in a second stage. In addition, we will have a small scintillator array to test and confirm the performance of the radio only trigger.

astro-ph.IM↗

arXiv2008

Cosmic rays studied with a hybrid high school detector array

The LORUN/NAHSA system is a pathfinder for hybrid cosmic ray research combined with education and outreach in the field of astro-particle physics. Particle detectors and radio antennae were mainly setup by students and placed on public buildings. After fully digital data acquisition, coincidence detections were selected. Three candidate events confirmed a working prototype, which can be multiplied to extend further particle detector arrays on high schools.

astro-ph↗

arXiv2008

Amplitude calibration of a digital radio antenna array for measuring cosmic ray air showers

Radio pulses are emitted during the development of air showers, where air showers are generated by ultra-high energy cosmic rays entering the Earth's atmosphere. These nanosecond short pulses are presently investigated by various experiments for the purpose of using them as a new detection technique for cosmic particles. For an array of 30 digital radio antennas (LOPES experiment) an absolute amplitude calibration of the radio antennas including the full electronic chain of the data acquisition system is performed, in order to estimate absolute values of the electric field strength for these short radio pulses. This is mandatory, because the measured radio signals in the MHz frequency range have to be compared with theoretical estimates and with predictions from Monte Carlo simulations to reconstruct features of the primary cosmic particle. A commercial reference radio emitter is used to estimate frequency dependent correction factors for each single antenna of the radio antenna array. The expected received power is related to the power recorded by the full electronic chain. Systematic uncertainties due to different environmental conditions and the described calibration procedure are of order 20%.

astro-ph↗

arXiv2004

LOPES Detecting Radio Emission from Cosmic Ray Air Showers

Radio pulses emitted in the atmosphere during the air shower development of high-energy primary cosmic rays were measured during the late 1960ies in the frequency range from 2 MHz to 520 MHz. Mainly due to difficulties with radio interference these measurements ceased in the late 1970ies. LOFAR (Low Frequency Array) is a new digital radio interferometer under development. Using high bandwidth ADCs and fast data processing it will be able to filter out most of the interference. By storing the whole waveform information in digital form one can analyze transient events like air showers even after they have been recorded. To test this new technology and to demonstrate its ability to measure air showers a "LOFAR Prototype Station" (LOPES) is set up to operate in conjunction with an existing air shower array (KASCADE-Grande). The first phase consisting of 10 antennas is already running. It operates in the frequency range of 40 to 80 MHz, using simple short dipole antennas and direct 2nd Nyquist sampling of the incoming wave. It has proven to be able to do simple astronomical measurements, like imaging of a solar burst. It has also demonstrated how digital interference suppression and beamforming can overcome the problem of radio interference and pick out air shower events.

astro-ph↗