Publications (48)
The shape of the radio wavefront of extensive air showers as measured with LOFAR
A. Corstanje, P. Schellart, A. Nelles +78
Extensive 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 emissi…
Resolving spatial and temporal shock structures using LOFAR observations of type II radio bursts
D. E. Morosan, I. C. Jebaraj, P. Zhang +6
Collisionless shocks are one of the most powerful particle accelerators in the Universe. In the heliosphere, type II solar radio bursts are signatures of electrons accelerated by c…
The peculiar radio galaxy 4C 35.06: a case for recurrent AGN activity?
A. Shulevski, R. Morganti, P. D. Barthel +85
Using 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…
The brightness and spatial distributions of terrestrial radio sources
A. R. Offringa, A. G. de Bruyn, S. Zaroubi +75
Faint undetected sources of radio-frequency interference (RFI) might become visible in long radio observations when they are consistently present over time. Thereby, they might obs…
LOFAR imaging of the solar corona during the 2015 March 20 solar eclipse
A. M. Ryan, P. T. Gallagher, E. P. Carley +12
The solar corona is a highly-structured plasma which can reach temperatures of more than ~2 MK. At low frequencies (decimetric and metric wavelengths), scattering and refraction of…
The LOFAR long baseline snapshot calibrator survey
J. Moldón, A. T. Deller, O. Wucknitz +82
Aims. An efficient means of locating calibrator sources for International LOFAR is developed and used to determine the average density of usable calibrator sources on the sky for s…
Source location and evolution of a multi-lane type II radio burst
P. Zucca, P. Zhang, K. Kozarev +8
Shocks in the solar corona can accelerate electrons that in turn generate radio emission known as type II radio bursts. The characteristics and morphology of these radio bursts in…
A large light-mass component of cosmic rays at 10^{17} - 10^{17.5} eV from radio observations
S. Buitink, A. Corstanje, H. Falcke +101
Cosmic 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 whet…
The Association of a J-burst with a Solar Jet
D. E. Morosan, P. T. Gallagher, R. A. Fallows +56
Context. The Sun is an active star that produces large-scale energetic events such as solar flares and coronal mass ejections and numerous smaller-scale events such as solar jets.…
LOFAR detections of low-frequency radio recombination lines towards Cassiopeia A
Ashish Asgekar, J. B. R. Oonk, S. Yatawatta +89
Cassiopeia A was observed using the Low-Band Antennas of the LOw Frequency ARray (LOFAR) with high spectral resolution. This allowed a search for radio recombination lines (RRLs) a…
Imaging Jupiter's radiation belts down to 127 MHz with LOFAR
J. N. Girard, P. Zarka, C. Tasse +71
Context. Observing Jupiter's synchrotron emission from the Earth remains today the sole method to scrutinize the distribution and dynamical behavior of the ultra energetic electron…
LOFAR imaging of Cygnus A -- Direct detection of a turnover in the hotspot radio spectra
J. P. McKean, L. E. H. Godfrey, S. Vegetti +75
The low-frequency radio spectra of the hotspots within powerful radio galaxies can provide valuable information about the physical processes operating at the site of the jet termin…
Multifrequency behaviour of the anomalous events of PSR J0922+0638
G. Shaifullah, C. Tiburzi, S. OsÅowski +10
PSR J0922+0638 (B0919+06) shows unexplained anomalous variations in the on-pulse phase, where the pulse appears to episodically move to an earlier longitude for a few tens of rotat…
Sub-arcsecond imaging with the International LOFAR Telescope I. Foundational calibration strategy and pipeline
L. K. Morabito, N. J. Jackson, S. Mooney +71
[abridged] The International LOFAR Telescope is an interferometer with stations spread across Europe. With baselines of up to ~2,000 km, LOFAR has the unique capability of achievin…
LOFAR MSSS: Detection of a low-frequency radio transient in 400 hrs of monitoring of the North Celestial Pole
A. J. Stewart, R. P. Fender, J. W. Broderick +99
We 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 Mult…
Propagation of energetic electrons from the corona into interplanetary space and type III radio emission
F. Breitling, G. Mann, C. Vocks
During solar flares a large amount of electrons with energies greater than 20 keV is generated with a production rate of typically s. A part of them is able to pro…
The LOFAR radio environment
A. R. Offringa, A. G. de Bruyn, S. Zaroubi +93
Aims: This paper discusses the spectral occupancy for performing radio astronomy with the Low-Frequency Array (LOFAR), with a focus on imaging observations. Methods: We have analys…
Suprathermal electron distributions in the solar transition region
C. Vocks, E. Dzifcakova, G. Mann
Suprathermal tails are a common feature of solar wind electron velocity distributions, and are expected in the solar corona. From the corona, suprathermal electrons can propagate t…
Discovery of Carbon Radio Recombination Lines in absorption towards Cygnus~A
J. B. R. Oonk, R. J. van Weeren, F. Salgado +100
We present the first detection of carbon radio recombination line absorption along the line of sight to Cygnus A. The observations were carried out with the LOw Frequency ARray in…
Synthetic IRIS spectra of the solar transition region: Effect of high-energy tails
E. Dzifcakova, C. Vocks, J. Dudik
The solar transition region satisfies the conditions for presence of non-Maxwellian electron energy distributions with high-energy tails at energies corresponding to the ionization…
Detecting cosmic rays with the LOFAR radio telescope
P. Schellart, A. Nelles, S. Buitink +102
The 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 interferom…
Initial LOFAR observations of Epoch of Reionization windows: II. Diffuse polarized emission in the ELAIS-N1 field
V. Jelic, A. G. de Bruyn, M. Mevius +106
This study aims to characterise the polarized foreground emission in the ELAIS-N1 field and to address its possible implications for the extraction of the cosmological 21-cm signal…
The LOFAR Tied-Array All-Sky Survey: Timing of 21 pulsars including the first binary pulsar discovered with LOFAR
C. M. Tan, C. G. Bassa, S. Cooper +18
We report on the multi-frequency timing observations of 21 pulsars discovered in the LOFAR Tied-Array All-Sky Survey (LOTAAS). The timing data were taken at central frequencies of…
The LOFAR Tied-Array All-Sky Survey: Timing of 35 radio pulsars and an overview of the properties of the LOFAR pulsar discoveries
E. van der Wateren, C. G. Bassa, S. Cooper +20
The LOFAR Tied-Array All-Sky Survey (LOTAAS) is the most sensitive untargeted radio pulsar survey performed at low radio frequencies (119--151\,MHz) to date and has discovered 76 n…
LOFAR low-band antenna observations of the 3C295 and Bootes fields: source counts and ultra-steep spectrum sources
R. J. van Weeren, W. L. Williams, C. Tasse +98
We present LOFAR Low Band observations of the Bootes and 3C295 fields. Our images made at 34, 46, and 62 MHz reach noise levels of 12, 8, and 5 mJy beam, making them the dee…
LOFAR observations of the quiet solar corona
C. Vocks, G. Mann, F. Breitling +9
The quiet solar corona emits meter-wave thermal bremsstrahlung. Coronal radio emission can only propagate above that radius, , where the local plasma frequency eqals the obse…
Combining the second data release of the European Pulsar Timing Array with low-frequency pulsar data
F. Iraci, A. Chalumeau, C. Tiburzi +46
Low-frequency radio data improve the sensitivity of pulsar timing arrays (PTAs) to propagation effects such as dispersion measure (DM) variations, enabling better noise characteriz…
Studying Galactic interstellar turbulence through fluctuations in synchrotron emission: First LOFAR Galactic foreground detection
M. Iacobelli, M. Haverkorn, E. Orrú +85
The characteristic outer scale of turbulence and the ratio of the random to ordered components of the magnetic field are key parameters to characterise magnetic turbulence in the i…
LOFAR: The LOw-Frequency ARray
M. P. van Haarlem, M. W. Wise, A. W. Gunst +197
LOFAR, 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…
Sub-arcsecond imaging with the International LOFAR Telescope: II. Completion of the LOFAR Long-Baseline Calibrator Survey
Neal Jackson, Shruti Badole, John Morgan +69
The Low-Frequency Array (LOFAR) Long-Baseline Calibrator Survey (LBCS) was conducted between 2014 and 2019 in order to obtain a set of suitable calibrators for the LOFAR array. In…
Separating Nightside Interplanetary and Ionospheric Scintillation with LOFAR
R. A. Fallows, M. M. Bisi, B. Forte +4
Observation of interplanetary scintillation (IPS) beyond Earth-orbit can be challenging due to the necessity to use low radio frequencies at which scintillation due to the ionosphe…
M87 at metre wavelengths: the LOFAR picture
F. de Gasperin, E. Orru', M. Murgia +92
M87 is a giant elliptical galaxy located in the centre of the Virgo cluster, which harbours a supermassive black hole of mass 6.4x10^9 M_sun, whose activity is responsible for the…
Shock location and CME 3D reconstruction of a solar type II radio burst with LOFAR
P. Zucca, D. E. Morosan, A. P. Rouillard +62
Type II radio bursts are evidence of shocks in the solar atmosphere and inner heliosphere that emit radio waves ranging from sub-meter to kilometer lengths. These shocks may be ass…
Wide-Band, Low-Frequency Pulse Profiles of 100 Radio Pulsars with LOFAR
M. Pilia, J. W. T. Hessels, B. W. Stappers +84
LOFAR offers the unique capability of observing pulsars across the 10-240 MHz frequency range with a fractional bandwidth of roughly 50%. This spectral range is well-suited for stu…
The impact of Solar wind variability on pulsar timing
C. Tiburzi, G. M. Shaifullah, C. G. Bassa +22
High-precision pulsar timing requires accurate corrections for dispersive delays of radio waves, parametrized by the dispersion measure (DM), particularly if these delays are varia…
Determining the acceleration regions of in situ electrons using remote radio and X-ray observations
D. E. Morosan, N. Dresing, C. Palmroos +13
Solar energetic particles in the heliosphere are produced by flaring processes on the Sun or shocks driven by coronal mass ejections. These particles are regularly detected remotel…
The LOFAR Multifrequency Snapshot Sky Survey (MSSS) I. Survey description and first results
G. H. Heald, R. F. Pizzo, E. Orrú +147
We 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 de…
Exploring the time variability of the Solar Wind using LOFAR pulsar data
S. C. Susarla, A. Chalumeau, C. Tiburzi +22
High-precision pulsar timing is highly dependent on precise and accurate modeling of any effects that impact the data. It was shown that commonly used Solar Wind models do not accu…
LOFAR tied-array imaging and spectroscopy of solar S bursts
D. E. Morosan, P. T. Gallagher, P. Zucca +50
Context. The Sun is an active source of radio emission that is often associated with energetic phenomena ranging from nanoflares to coronal mass ejections (CMEs). At low radio freq…
LBCS: the LOFAR Long-Baseline Calibrator Survey
N. Jackson, A. Tagore, A. Deller +76
(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…
LOFAR tied-array imaging of Type III solar radio bursts
D. E. Morosan, P. T. Gallagher, P. Zucca +82
The 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 (<…
Cassiopeia A, Cygnus A, Taurus A, and Virgo A at ultra-low radio frequencies
F. de Gasperin, J. Vink, J. P. McKean +49
The four persistent radio sources in the northern sky with the highest flux density at metre wavelengths are Cassiopeia A, Cygnus A, Taurus A, and Virgo A; collectively they are ca…
LOFAR discovery of a quiet emission mode in PSR B0823+26
C. Sobey, N. J. Young, J. W. T. Hessels +91
PSR 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.…
The LOFAR Pilot Surveys for Pulsars and Fast Radio Transients
Thijs Coenen, Joeri van Leeuwen, Jason W. T. Hessels +87
We have conducted two pilot surveys for radio pulsars and fast transients with the Low-Frequency Array (LOFAR) around 140 MHz and here report on the first low-frequency fast-radio…
Dispersion measure variability for 36 millisecond pulsars at 150MHz with LOFAR
J. Y. Donner, J. P. W. Verbiest, C. Tiburzi +19
Radio pulses from pulsars are affected by plasma dispersion, which results in a frequency-dependent propagation delay. Variations in the magnitude of this effect lead to an additio…
Measuring a Cherenkov ring in the radio emission from air showers at 110-190 MHz with LOFAR
A. Nelles, P. Schellart, S. Buitink +66
Measuring 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 tim…
Probing Atmospheric Electric Fields in Thunderstorms through Radio Emission from Cosmic-Ray-Induced Air Showers
P. Schellart, T. N. G. Trinh, S. Buitink +71
We 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 radical…
LOFAR 144-MHz follow-up observations of GW170817
J. W. Broderick, T. W. Shimwell, K. Gourdji +66
We present low-radio-frequency follow-up observations of AT 2017gfo, the electromagnetic counterpart of GW170817, which was the first binary neutron star merger to be detected by A…