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39 papers
Spectral indices in active galactic nuclei as seen by Apertif and LOFAR
A. M. Kutkin, R. Morganti, T. A. Oosterloo +5
We present two new radio continuum images obtained with Apertif at 1.4 GHz. The images, produced with a direction-dependent calibration pipeline, cover 136 square degrees of the Lo…
Real-time station monitor and stationtest pipelines for LOFAR 2.0
Jun Wang, M. J. Norden, P. Donker
LOFAR is a low-frequency array distributed across several European countries. Each LOFAR station contains thousands of antennas and associated electronics, making monitoring and th…
Continuum source catalog for the first APERTIF data release
A. M. Kutkin, T. A. Oosterloo, R. Morganti +25
The first data release of Apertif survey contains 3074 radio continuum images covering a thousand square degrees of the sky. The observations were performed during August 2019 to J…
First release of Apertif imaging survey data
Elizabeth A. K. Adams, B. Adebahr, W. J. G. de Blok +56
(Abridged) Apertif is a phased-array feed system for WSRT, providing forty instantaneous beams over 300 MHz of bandwidth. A dedicated survey program started on 1 July 2019, with th…
Characterising the Apertif primary beam response
H. Dénes, K. M. Hess, E. A. K. Adams +27
Context. Phased Array Feeds (PAFs) are multi element receivers in the focal plane of a telescope that make it possible to form simultaneously multiple beams on the sky by combining…
The Apertif science verification campaign - Characteristics of polarised radio sources
B. Adebahr, A. Berger, E. A. K. Adams +24
We analyse five early science datasets from the APERture Tile in Focus (Apertif) phased array feed system to verify the polarisation capabilities of Apertif in view of future large…
A fast radio burst with sub-millisecond quasi-periodic structure
Inés Pastor-Marazuela, Joeri van Leeuwen, Anna Bilous +31
Fast radio bursts (FRBs) are extragalactic radio transients of extraordinary luminosity. Studying the diverse temporal and spectral behaviour recently observed in a number of FRBs…
Apertif, Phased Array Feeds for the Westerbork Synthesis Radio Telescope
W. A. van Cappellen, T. A. Oosterloo, M. A. W. Verheijen +87
We describe the APERture Tile In Focus (Apertif) system, a phased array feed (PAF) upgrade of the Westerbork Synthesis Radio Telescope which has transformed this telescope into a h…
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…
The LOFAR LBA Sky Survey I. survey description and preliminary data release
F. de Gasperin, W. L. Williams, P. Best +38
LOFAR is the only radio telescope that is presently capable of high-sensitivity, high-resolution (<1 mJy/b and <15") observations at ultra-low frequencies (<100 MHz). To utilise th…
Apertif view of the OH Megamaser IRAS 10597+5926: OH 18 cm satellite lines in wide-area HI surveys
Kelley M. Hess, H. Roberts, H. Dénes +26
We present the serendipitous detection of the two main OH maser lines at 1667 and 1665 MHz associated with IRAS 10597+5926 at z = 0.19612 in the untargeted Apertif Wide-area Extrag…
Chromatic periodic activity down to 120 MHz in a Fast Radio Burst
Inés Pastor-Marazuela, Liam Connor, Joeri van Leeuwen +34
Fast radio bursts (FRBs) are extragalactic astrophysical transients whose brightness requires emitters that are highly energetic, yet compact enough to produce the short, milliseco…
Extreme intra-hour variability of the radio source J1402+5347 discovered with Apertif
T. A. Oosterloo, H. K. Vedantham, A. M. Kutkin +27
The propagation of radio waves from distant compact radio sources through turbulent interstellar plasma in our Galaxy causes these sources to twinkle, a phenomenon called interstel…
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…
Repeating fast radio bursts with WSRT/Apertif
L. C. Oostrum, Y. Maan, J. van Leeuwen +40
Repeating fast radio bursts (FRBs) present excellent opportunities to identify FRB progenitors and host environments, as well as decipher the underlying emission mechanism. Detaile…
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…
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…
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…
Broadband Meter-Wavelength Observations of Ionospheric Scintillation
R. A. Fallows, W. A. Coles, D. McKay +22
Intensity scintillations of cosmic radio sources are used to study astrophysical plasmas like the ionosphere, the solar wind, and the interstellar medium. Normally these observatio…
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…
Calibrating the absolute amplitude scale for air showers measured at LOFAR
A. Nelles, J. R. Hörandel, T. Karskens +74
Air 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…
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 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…
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…