Results for "J. R. Hörandel"

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Forbush decreases and solar events seen in the 10 - 20GeV energy range by the Karlsruhe Muon TelescopeOct 27 2008Since 1993, a muon telescope located at Forschungszentrum Karlsruhe (Karlsruhe Muon Telescope) has been recording the flux of single muons mostly originating from primary cosmic-ray protons with dominant energies in the 10 - 20 GeV range. The data are ... More
Cosmic-ray spectral anomaly at GeV-TeV energies as due to re-acceleration by weak shocks in the GalaxyAug 06 2013Recent cosmic-ray measurements by the ATIC, CREAM and PAMELA experiments have found an apparent hardening of the energy spectrum at TeV energies. Although the origin of the hardening is not clearly understood, possible explanations include hardening in ... More
On the point source approximation of nearby cosmic-ray sourcesSep 26 2011In this paper, we check in detail the validity of the widely adopted point source approximation for nearby cosmic-ray (CR) sources. Under an energy independent escape model for CRs from the sources, we show that for young nearby sources, the point source ... More
Universality of electron-positron distributions in extensive air showersFeb 03 2009Using a large set of simulated extensive air showers, we investigate universality features of electron and positron distributions in very-high-energy cosmic-ray air showers. Most particle distributions depend only on the depth of the shower maximum and ... More
GeV-TeV cosmic-ray spectral anomaly as due to re-acceleration by weak shocks in the GalaxyApr 14 2014Recent cosmic-ray measurements have found an anomaly in the cosmic-ray energy spectrum at GeV-TeV energies. Although the origin of the anomaly is not clearly understood, suggested explanations include effect of cosmic-ray source spectrum, propagation ... More
Revisiting the hardening of the cosmic-ray energy spectrum at TeV energiesApr 04 2013Aug 05 2013Measurements of cosmic rays by experiments such as ATIC, CREAM, and PAMELA indicate a hardening of the cosmic-ray energy spectrum at TeV energies. In our recent work (Thoudam & H\"orandel 2012a), we showed that the hardening can be due to the effect of ... More
Nearby supernova remnants and the cosmic-ray spectral hardening at high energiesDec 13 2011Dec 16 2011Recent measurements of cosmic-ray spectra of several individual nuclear species by the CREAM, TRACER, and ATIC experiments indicate a change in the spectral index of the power laws at TeV energies. Possible explanations among others include non linear ... More
A possible correlation between the high energy electron spectrum and the cosmic-ray secondary-to-primary ratiosFeb 04 2011Recent observations of high energy cosmic-ray electrons by the Fermi-LAT and the HESS experiments between $20$ GeV and $5$ TeV have found that the energy spectrum closely follow a broken power-law with a break at around $1$ TeV. On the other hand, measurements ... More
Cosmic-ray energy spectrum and composition up to the ankle - the case for a second Galactic componentMay 10 2016Nov 11 2016We have carried out a detailed study to understand the observed energy spectrum and composition of cosmic rays with energies up to ~10^18 eV. Our study shows that a single Galactic component with subsequent energy cut-offs in the individual spectra of ... More
Cosmic-ray energy spectrum and composition up to the ankle - the case for a second Galactic componentMay 10 2016We have carried out a detailed study to understand the observed energy spectrum and composition of cosmic rays with energies up to ~10^18 eV. Our study shows that a single Galactic component with subsequent energy cut-offs in the individual spectra of ... More
Prospects for direct cosmic ray mass measurements through the Gerasimova-Zatsepin effectApr 16 2008The Solar radiation field may break apart ultra high energy cosmic nuclei, after which both remnants will be deflected in the interplanetary magnetic field in different ways. This process is known as the Gerasimova-Zatsepin effect after its discoverers. ... More
Central Acceptance Testing for Camera Technologies for CTAAug 25 2015The Cherenkov Telescope Array (CTA) is an international initiative to build the next generation ground based very-high energy gamma-ray observatory. It will consist of telescopes of three different sizes, employing several different technologies for the ... More
Air Shower Measurements with LOFARMar 13 2009Air 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, ... More
An analytic description of the radio emission of air showers based on its emission mechanismsJun 10 2018Sep 28 2018Ultra-high energy cosmic rays can be measured through the detection of radio-frequency radiation from air showers. The radio-frequency emission originates from deflections of the air-shower particles in the geomagnetic field and from a time-varying negative ... More
Prospects for determining air shower characteristics through geosynchrotron emission arrival timesApr 05 2010Using simulations of geosynchrotron radiation from extensive air showers, we present a relation between the shape of the geosynchrotron radiation front and the distance of the observer to the maximum of the air shower. By analyzing the relative arrival ... More
Determining the fraction of cosmic-ray protons at ultra-high energies with cosmogenic neutrinosJan 07 2019Cosmogenic neutrinos are produced when ultra-high-energy cosmic rays (UHECRs) interact with cosmological photon fields. Limits on the diffuse flux of these neutrinos can be used to constrain the fraction of protons arriving at Earth with energies $E_{p} ... More
The boron-to-carbon abundance ratio and Galactic propagation of cosmic radiationApr 27 2012In two long-duration balloon flights in 2003 and 2006, the TRACER cosmic-ray detector has measured the energy spectra and the absolute intensities of the cosmic-ray nuclei from boron (Z = 5) to iron (Z = 26) up to very high energies. In particular, the ... More
Interactions of Cosmic Rays in the Atmosphere: Growth Curves RevisitedSep 23 2013Measurements of cosmic-ray abundances on balloons are affected by interactions in the residual atmosphere above the balloon. Corrections for such interactions are particularly important for observations of rare secondary particles such as boron, antiprotons ... More
Realtime processing of LOFAR data for the detection of nano-second pulses from the MoonDec 20 2016The low flux of the ultra-high energy cosmic rays (UHECR) at the highest energies provides a challenge to answer the long standing question about their origin and nature. Even lower fluxes of neutrinos with energies above $10^{22}$ eV are predicted in ... More
Measurement of the cosmic-ray energy spectrum above $10^{16}$ eV with the LOFAR Radboud Air Shower ArrayJun 30 2015Jul 01 2015The energy reconstruction of extensive air showers measured with the LOFAR Radboud Air Shower Array (LORA) is presented in detail. LORA is a particle detector array located in the center of the LOFAR radio telescope in the Netherlands. The aim of this ... More
A method for high precision reconstruction of air shower Xmax using two-dimensional radio intensity profilesAug 29 2014Sep 01 2014The mass composition of cosmic rays contains important clues about their origin. Accurate measurements are needed to resolve long-standing issues such as the transition from Galactic to extragalactic origin, and the nature of the cutoff observed at the ... More
The effect of the atmospheric refractive index on the radio signal of extensive air showersJan 25 2017For the interpretation of measurements of radio emission from extensive air showers, an important systematic uncertainty arises from natural variations of the atmospheric refractive index $n$. At a given altitude, the refractivity $N=10^6\, (n-1)$ can ... More
Search for Cosmic Particles with the Moon and LOFARSep 21 2016The low flux of the ultra-high energy cosmic rays (UHECR) at the highest energies provides a challenge to answer the long standing question about their origin and nature. A significant increase in the number of detected UHECR is expected to be achieved ... More
LOFAR: Detecting Cosmic Rays with a Radio TelescopeSep 27 2011LOFAR (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 ... More
Status of the Lunar Detection Mode for Cosmic Particles of LOFARMar 20 2019Cosmic particles hitting Earth's moon produce radio emission via the Askaryan effect. If the resulting radio ns-pulse can be detected by radio telescopes, this technique potentially increases the available collective area for ZeV scale particles by several ... More
Timing calibration and spectral cleaning of LOFAR time series dataMar 28 2016We describe a method for spectral cleaning and timing calibration of short voltage time series data from individual radio interferometer receivers. It makes use of the phase differences in Fast Fourier Transform (FFT) spectra across antenna pairs. For ... More
The radio emission pattern of air showers as measured with LOFAR - a tool for the reconstruction of the energy and the shower maximumNov 28 2014Apr 13 2015The pattern of the radio emission of air showers is finely sampled with the Low-Frequency ARray (LOFAR). A set of 382 measured air showers is used to test a fast, analytic parameterization of the distribution of pulse powers. Using this parameterization ... More
Polarized radio emission from extensive air showers measured with LOFARJun 05 2014Sep 09 2014We present LOFAR measurements of radio emission from extensive air showers. We find that this emission is strongly polarized, with a median degree of polarization of nearly $99\%$, and that the angle between the polarization direction of the electric ... More
Cosmic Ray Physics with the LOFAR Radio TelescopeMar 20 2019The LOFAR radio telescope is able to measure the radio emission from cosmic ray induced air showers with hundreds of individual antennas. This allows for precision testing of the emission mechanisms for the radio signal as well as determination of the ... More
LORA: A scintillator array for LOFAR to measure extensive air showersAug 19 2014The measurement of the radio emission from extensive air showers, induced by high-energy cosmic rays is one of the key science projects of the LOFAR radio telescope. The LOfar Radboud air shower Array (LORA) has been installed in the core of LOFAR in ... More
An air shower array for LOFAR: LORAFeb 04 2011LOFAR 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. ... More
Energy spectra of primary and secondary cosmic-ray nuclei measured with TRACERAug 24 2011The TRACER cosmic-ray detector, first flown on long-duration balloon (LDB) in 2003 for observations of the major primary cosmic-ray nuclei from oxygen (Z=8) to iron (Z=26), has been upgraded to also measure the energies of the lighter nuclei, including ... More
Simulation of the Radiation Energy Release in Air ShowersSep 19 2016A 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 ... More
Simulation of Radiation Energy Release in Air ShowersJun 06 2016Sep 19 2016A 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 ... More
Radio detection of air showers with LOFAR and AERASep 16 2015High-energy cosmic rays impinging onto the atmosphere of the Earth initiate extensive air showers. With the LOFAR radio telescope and the Auger Engineering Radio Array (AERA) at the Pierre Auger Observatory radio emission from air showers is detected. ... More
Influence of Atmospheric Electric Fields on the Radio Emission from Extensive Air ShowersNov 10 2015The atmospheric electric fields in thunderclouds have been shown to significantly modify the intensity and polarization patterns of the radio footprint of cosmic-ray-induced extensive air showers. Simulations indicated a very non-linear dependence of ... More
IMAGINE: modeling the Galactic magnetic fieldMar 11 2019The IMAGINE Consortium aims to bring modeling of the magnetic field of the Milky Way to a next level, by using Bayesian inference. IMAGINE includes an open-source modular software pipeline that optimizes parameters in a user-defined Galactic magnetic ... More
Anomaly in the cosmic-ray energy spectrum at GeV-TeV energiesMay 04 2015Recent measurements of cosmic rays by various experiments have found that the energy spectrum of cosmic rays is harder in the TeV region than at GeV energies. The origin of the spectral hardening is not clearly understood. In this paper, we discuss the ... More
Measurement of the circular polarization in radio emission from extensive air showers confirms emission mechanismsNov 02 2016Nov 19 2016We report here on a novel analysis of the complete set of four Stokes parameters that uniquely determine the linear and/or circular polarization of the radio signal for an extensive air shower. The observed dependency of the circular polarization on azimuth ... More
Measurement of the circular polarization in radio emission from extensive air showers confirms emission mechanismsNov 02 2016We report here on a novel analysis of the complete set of four Stokes parameters that uniquely determine the linear and/or circular polarization of the radio signal for an extensive air shower. The observed dependency of the circular polarization on azimuth ... More
Precise Measurement of the Absolute Yield of Fluorescence Photons in Atmospheric GasesJan 19 2011We have performed a measurement of the absolute yield of fluorescence photons at the Fermilab Test Beam. A systematic uncertainty at 5% level was achieved by the use of Cherenkov radiation as a reference calibration light source. A cross-check was performed ... More
Precise measurement of the absolute fluorescence yield of the 337 nm band in atmospheric gasesOct 25 2012A measurement of the absolute fluorescence yield of the 337 nm nitrogen band, relevant to ultra-high energy cosmic ray (UHECR) detectors, is reported. Two independent calibrations of the fluorescence emission induced by a 120 GeV proton beam were employed: ... More
Inferring Galactic magnetic field model parameters using IMAGINE - An Interstellar MAGnetic field INference EngineJan 12 2018Context. The Galactic magnetic field (GMF) has a huge impact on the evolution of the Milky Way. Yet currently there exists no standard model for it, as its structure is not fully understood. In the past many parametric GMF models of varying complexity ... More
Measuring a Cherenkov ring in the radio emission from air showers at 110-190 MHz with LOFARNov 25 2014Measuring radio emission from air showers offers a novel way to determine properties of the primary cosmic rays such as their mass and energy. Theory predicts that relativistic time compression effects lead to a ring of amplified emission which starts ... More
KASCADE-Grande measurements of energy spectra for elemental groups of cosmic raysJun 26 2013The KASCADE-Grande air shower experiment [W. Apel, et al. (KASCADE-Grande collaboration), Nucl. Instrum. Methods A 620 (2010) 202] consists of, among others, a large scintillator array for measurements of charged particles, Nch, and of an array of shielded ... More
The KASCADE Cosmic-ray Data Centre KCDC: Granting Open Access to Astroparticle Physics Research DataJun 14 2018The `KASCADE Cosmic ray Data Centre' is a web portal (\url{https://kcdc.ikp.kit.edu}), where the data of the astroparticle physics experiment KASCADE-Grande are made available for the interested public. The KASCADE experiment was a large-area detector ... More
Sensitivity of KASCADE-Grande data to hadronic interaction modelsSep 24 2010KASCADE-Grande is a large detector array dedicated for studies of high-energy cosmic rays in the primary energy range from 100 TeV to 1 EeV. The multi-detector concept of the experimental set-up offers the possibility to measure simultaneously various ... More
Longitudinal EAS-Development Studies in the Air-Shower Experiment KASCADE-GrandeOct 13 2010A large area (128 m^2) Muon Tracking Detector (MTD), located within the KASCADE experiment, has been built with the aim to identify muons (E_mu > 0.8 GeV) and their directions in extensive air showers by track measurements under more than 18 r.l. shielding. ... More
Ankle-like Feature in the Energy Spectrum of Light Elements of Cosmic Rays Observed with KASCADE-GrandeApr 26 2013Recent results of the KASCADE-Grande experiment provided evidence for a mild knee-like structure in the all-particle spectrum of cosmic rays at $E = 10^{16.92 \pm 0.10} \, \mathrm{eV}$, which was found to be due to a steepening in the flux of heavy primary ... More
Improved absolute calibration of LOPES measurements and its impact on the comparison with REAS 3.11 and CoREAS simulationsJul 27 2015Dec 18 2015LOPES was a digital antenna array detecting the radio emission of cosmic-ray air showers. The calibration of the absolute amplitude scale of the measurements was done using an external, commercial reference source, which emits a frequency comb with defined ... More
KASCADE-Grande Limits on the Isotropic Diffuse Gamma-Ray Flux between 100 TeV and 1 EeVOct 08 2017KASCADE and KASCADE-Grande were multi-detector installations to measure individual air showers of cosmic rays at ultra-high energy. Based on data sets measured by KASCADE and KASCADE-Grande, 90% C.L. upper limits to the flux of gamma-rays in the primary ... More
The <lnA> study in the primary energy range 10^{16} - 10^{17} eV with the Muon Tracking Detector in the KASCADE-Grande experimentAug 09 2013The KASCADE-Grande Muon Tracking Detector enables with high accuracy the measurement of directions of EAS muons with energy above 0.8 GeV and up to 700 m distance from the shower centre. Reconstructed muon tracks are used to investigate muon pseudorapidity ... More
Cosmic Ray Measurements with LOPES: Status and Recent Results (ARENA 2012)Jan 11 2013LOPES is a digital antenna array at the Karlsruhe Institute of Technology, Germany, for cosmic-ray air-shower measurements. Triggered by the co-located KASCADE-Grande air-shower array, LOPES detects the radio emission of air showers via digital radio ... More
The KASCADE-Grande experiment: measurements of the all-particle energy spectrum of cosmic raysSep 23 2010The all-particle energy spectrum as measured by the KASCADE-Grande experiment for E = 10^{16} - 10^{18} eV is presented within the framework of the QGSJET II/FLUKA hadronic interaction models. Three different methods were applied based on the muon size ... More
Probing the evolution of the EAS muon content in the atmosphere with KASCADE-GrandeJan 17 2018The evolution of the muon content of very high energy air showers (EAS) in the atmosphere is investigated with data of the KASCADE-Grande observatory. For this purpose, the muon attenuation length in the atmosphere is obtained to $\Lambda_\mu = 1256 \, ... More
Revised absolute amplitude calibration of the LOPES experimentAug 14 2015One of the main aims of the LOPES experiment was the evaluation of the absolute amplitude of the radio signal of air showers. This is of special interest since the radio technique offers the possibility for an independent and highly precise determination ... More
Investigation of the radio wavefront of air showers with LOPES measurements and CoREAS simulations (ARENA 2014)Jul 28 2015We investigated the radio wavefront of cosmic-ray air showers with LOPES measurements and CoREAS simulations: the wavefront is of approximately hyperbolic shape and its steepness is sensitive to the shower maximum. For this study we used 316 events with ... More
Reconstruction of the energy and depth of maximum of cosmic-ray air-showers from LOPES radio measurementsAug 11 2014LOPES is a digital radio interferometer located at Karlsruhe Institute of Technology (KIT), Germany, which measures radio emission from extensive air showers at MHz frequencies in coincidence with KASCADE-Grande. In this article, we explore a method (slope ... More
Comparing LOPES measurements of air-shower radio emission with REAS 3.11 and CoREAS simulationsSep 19 2013Dec 18 2015Cosmic ray air showers emit radio pulses at MHz frequencies, which can be measured with radio antenna arrays - like LOPES at the Karlsruhe Institute of Technology in Germany. To improve the understanding of the radio emission, we test theoretical descriptions ... More
Vectorial Radio Interferometry with LOPES 3DAug 12 2013One successful detection technique for high-energy cosmic rays is based on the radio signal emitted by the charged particles in an air shower. The LOPES experiment at Karlsruhe Institute of Technology, Germany, has made major contributions to the evolution ... More
LOPES 3D - vectorial measurements of radio emission from cosmic ray induced air showersMar 28 2013LOPES 3D is able to measure all three components of the electric field vector of the radio emission from air showers. This allows a better comparison with emission models. The measurement of the vertical component increases the sensitivity to inclined ... More
Comparison of LOPES data and CoREAS simulations using a full detector simulation (ICRC2013)Aug 12 2013The LOPES experiment at the Karlsruhe Institute of Technology, Germany, has been measuring radio emission of air showers for almost 10 years. For a better understanding of the emission process a detailed comparison of data with simulations is necessary. ... More
Detecting cosmic rays with the LOFAR radio telescopeNov 06 2013The low frequency array (LOFAR), is the first radio telescope designed with the capability to measure radio emission from cosmic-ray induced air showers in parallel with interferometric observations. In the first $\sim 2\,\mathrm{years}$ of observing, ... More
Recent results from the KASCADE-Grande cosmic-ray experiment --- Test of hadronic interaction models with air-shower dataNov 07 2017Nov 12 2017Cosmic rays provide an unique approach to study hadronic interactions at high energies in the kinematic forward direction. The KASCADE air shower experiment was the first to conduct quantitative tests of hadronic interactions with air shower data. A brief ... More
Investigation on the energy and mass composition of cosmic rays using LOPES radio dataSep 10 2013The sensitivity to the mass composition as well as the reconstruction of the energy of the primary particle are explored here by leveraging the features of the radio lateral distribution function. For the purpose of this analysis, a set of events measured ... More
Mass sensitivity in the radio lateral distribution functionJul 31 2013Measuring the mass composition of ultra-high energy cosmic rays is one of the main tasks in the cosmic rays field. Here we are exploring the composition signature in the coherent electromagnetic emission from extensive air showers, detected in the MHz ... More
LOPES 3D reconfiguration and first measurementsMar 28 2013The Radio detection technique of high-energy cosmic rays is based on the radio signal emitted by the charged particles in an air shower due to their deflection in the Earth's magnetic field. The LOPES experiment at Karlsruhe Institute of Technology, Germany ... More
Experimental evidence for the sensitivity of the air-shower radio signal to the longitudinal shower developmentMar 18 2012We 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 ... More
LOPES-3D, an antenna array for full signal detection of air-shower radio emissionMar 27 2013To better understand the radio signal emitted by extensive air-showers and to further develop the radio detection technique of high-energy cosmic rays, the LOPES experiment was reconfigured to LOPES-3D. LOPES-3D is able to measure all three vectorial ... More
The wavefront of the radio signal emitted by cosmic ray air showersApr 12 2014Aug 07 2014Analyzing measurements of the LOPES antenna array together with corresponding CoREAS simulations for more than 300 measured events with energy above $10^{17}\,$eV and zenith angles smaller than $45^\circ$, we find that the radio wavefront of cosmic-ray ... More
Reconstructing energy and Xmax of cosmic ray air showers using the radio lateral distribution measured with LOPESJul 31 2013The LOPES experiment, a digital radio interferometer located at KIT (Karlsruhe Institute of Technology), obtained remarkable results for the detection of radio emission from extensive air showers at MHz frequencies. Features of the radio lateral distribution ... More
Thunderstorm Observations by Air-Shower Radio Antenna ArraysMar 28 2013Relativistic, charged particles present in extensive air showers lead to a coherent emission of radio pulses which are measured to identify the shower initiating high-energy cosmic rays. Especially during thunderstorms, there are additional strong electric ... More
On noise treatment in radio measurements of cosmic ray air showersSep 17 2010Precise 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 ... More
Calibrating the absolute amplitude scale for air showers measured at LOFARJul 31 2015Dec 28 2015Air showers induced by cosmic rays create nanosecond pulses detectable at radio frequencies. These pulses have been measured successfully in the past few years at the LOw Frequency ARray (LOFAR) and are used to study the properties of cosmic rays. For ... More
The peculiar radio galaxy 4C 35.06: a case for recurrent AGN activity?Apr 24 2015Using observations obtained with the LOw Fequency ARray (LOFAR), the Westerbork Synthesis Radio Telescope (WSRT) and archival Very Large Array (VLA) data, we have traced the radio emission to large scales in the complex source 4C 35.06 located in the ... More
LOFAR discovery of a quiet emission mode in PSR B0823+26May 12 2015PSR B0823+26, a 0.53-s radio pulsar, displays a host of emission phenomena over timescales of seconds to (at least) hours, including nulling, subpulse drifting, and mode-changing. Studying pulsars like PSR B0823+26 provides further insight into the relationship ... More
LOFAR Sparse Image ReconstructionJun 27 2014Mar 06 2015Context. The LOw Frequency ARray (LOFAR) radio telescope is a giant digital phased array interferometer with multiple antennas distributed in Europe. It provides discrete sets of Fourier components of the sky brightness. Recovering the original brightness ... More
Imaging Jupiter's radiation belts down to 127 MHz with LOFARNov 30 2015Context. Observing Jupiter's synchrotron emission from the Earth remains today the sole method to scrutinize the distribution and dynamical behavior of the ultra energetic electrons magnetically trapped around the planet (because in-situ particle data ... More
Probing Atmospheric Electric Fields in Thunderstorms through Radio Emission from Cosmic-Ray-Induced Air ShowersApr 22 2015We present measurements of radio emission from cosmic ray air showers that took place during thunderstorms. The intensity and polarization patterns of these air showers are radically different from those measured during fair-weather conditions. With the ... More
The shape of the radio wavefront of extensive air showers as measured with LOFARApr 15 2014Jun 08 2014Extensive air showers, induced by high energy cosmic rays impinging on the Earth's atmosphere, produce radio emission that is measured with the LOFAR radio telescope. As the emission comes from a finite distance of a few kilometers, the incident wavefront ... More
LBCS: the LOFAR Long-Baseline Calibrator SurveyAug 06 2016Sep 09 2016(abridged). We outline LBCS (the LOFAR Long-Baseline Calibrator Survey), whose aim is to identify sources suitable for calibrating the highest-resolution observations made with the International LOFAR Telescope, which include baselines >1000 km. Suitable ... More
A comparison of the cosmic-ray energy scales of Tunka-133 and KASCADE-Grande via their radio extensions Tunka-Rex and LOPESOct 26 2016Oct 27 2016The radio technique is a promising method for detection of cosmic-ray air showers of energies around $100\,$PeV and higher with an array of radio antennas. Since the amplitude of the radio signal can be measured absolutely and increases with the shower ... More
Lunar occultation of the diffuse radio sky: LOFAR measurements between 35 and 80 MHzJul 16 2014We present radio observations of the Moon between $35$ and $80$ MHz to demonstrate a novel technique of interferometrically measuring large-scale diffuse emission extending far beyond the primary beam (global signal) for the first time. In particular, ... More
LOFAR tied-array imaging of Type III solar radio burstsJul 16 2014The Sun is an active source of radio emission which is often associated with energetic phenomena such as solar flares and coronal mass ejections (CMEs). At low radio frequencies (<100 MHz), the Sun has not been imaged extensively because of the instrumental ... More
A large light-mass component of cosmic rays at 10^{17} - 10^{17.5} eV from radio observationsMar 04 2016May 01 2016Cosmic rays are the highest energy particles found in nature. Measurements of the mass composition of cosmic rays between 10^{17} eV and 10^{18} eV are essential to understand whether this energy range is dominated by Galactic or extragalactic sources. ... More
LOFAR MSSS: Detection of a low-frequency radio transient in 400 hrs of monitoring of the North Celestial PoleNov 30 2015We present the results of a four-month campaign searching for low-frequency radio transients near the North Celestial Pole with the Low-Frequency Array (LOFAR), as part of the Multifrequency Snapshot Sky Survey (MSSS). The data were recorded between 2011 ... More
The LOFAR Multifrequency Snapshot Sky Survey (MSSS) I. Survey description and first resultsSep 03 2015We present the Multifrequency Snapshot Sky Survey (MSSS), the first northern-sky LOFAR imaging survey. In this introductory paper, we first describe in detail the motivation and design of the survey. Compared to previous radio surveys, MSSS is exceptional ... More
The late time structure of high density contrast, single mode Richtmyer-Meshkov flowJul 19 2016We study the late time flow structure of Richtmyer-Meshkov instability. Recent numerical work has suggested a self-similar collapse of the development of this instability at late times, independent of the initial surface profile. Using the form of collapse ... More
Subdirect products of finitely presented metabelian groupsJun 13 2011Jul 15 2011There has been substantial investigation in recent years of subdirect products of limit groups and their finite presentability and homological finiteness properties. To contrast the results obtained for limit groups, Baumslag, Bridson, Holt and Miller ... More
An addendum to `A rigidity property for the set of all characters induced by valuations'May 28 2013This corrects and amplifies some comments made in a paper by Robert Bieri and the author with the above title.
LOFAR: The LOw-Frequency ARrayMay 15 2013May 19 2013LOFAR, the LOw-Frequency ARray, is a new-generation radio interferometer constructed in the north of the Netherlands and across europe. Utilizing a novel phased-array design, LOFAR covers the largely unexplored low-frequency range from 10-240 MHz and ... More
A parameterization for the radio emission of air showers as predicted by CoREAS simulations and applied to LOFAR measurementsFeb 12 2014Jun 19 2014Measuring radio emission from air showers provides excellent opportunities to directly measure all air shower properties, including the shower development. To exploit this in large-scale experiments, a simple and analytic parameterization of the distribution ... More
Hard thermal loops in long wave-length and static external gravitational fieldsJan 10 2013We study, in the long wave-length and static limits, the structure of the n-point graviton functions at high temperature. Using the gauge and Weyl invariance of the theory, we derive a simple expression for the hard thermal amplitudes in these two limits. ... More
An AdS/QCD holographic wavefunction for the rho meson and diffractive rho meson electroproductionMar 27 2012Jul 18 2012We show that AdS/QCD generates predictions for the rate of diffractive rho meson electroproduction that are in agreement with data collected at the HERA electron-proton collider.
Phenomenology of Distribution Amplitudes for the rho mesonDec 23 2011We report on a successful extraction of the twist-2 and twist-3 Distribution Amplitudes (DAs) of the rho meson using the HERA data on diffractive rho photoproduction. We extract these DAs using several Colour Glass Condensate (CGC) inspired and a Regge ... More
Constraining the rho meson wavefunctionDec 22 2010Diffractive rho meson production has been identified as one of the important processes where saturation can be probed at a future Electron-Ion Collider (EIC). A source of uncertainty in making predictions for this process lies within the assumed form ... More
Scaling Laws for Fluxon Formation in Annular Josephson Tunnel JunctionsJan 16 2003It has been argued by Zurek and Kibble that the likelihood of producing defects in a continuous phase transition depends in a characteristic way on the quench rate. In this paper we discuss our experiment for measuring the Zurek-Kibble scaling exponent ... More
Simple deterministic dynamical systems with fractal diffusion coefficientsJul 10 1998We analyze a simple model of deterministic diffusion. The model consists of a one-dimensional periodic array of scatterers in which point particles move from cell to cell as defined by a piecewise linear map. The microscopic chaotic scattering process ... More
Simple Maps with Fractal Diffusion CoefficientsAug 03 1994Dec 16 1994We consider chains of one-dimensional, piecewise linear, chaotic maps with uniform slope. We study the diffusive behaviour of an initially nonuniform distribution of points as a function of the slope of the map by solving Frobenius-Perron equation. For ... More