A. M. Scaife - University Southampton

A. M. Scaife
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Name
A. M. Scaife
Affiliation
University Southampton
City
Farmingville
Country
United States

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Astrophysics of Galaxies (27)
 
Cosmology and Nongalactic Astrophysics (14)
 
Instrumentation and Methods for Astrophysics (12)
 
High Energy Astrophysical Phenomena (11)
 
Solar and Stellar Astrophysics (9)
 
Statistics - Applications (1)
 
High Energy Physics - Experiment (1)
 
Earth and Planetary Astrophysics (1)

Publications Authored By A. M. Scaife

The new generation of low-frequency radio telescopes, such as the Low Frequency Array (LOFAR: a Square Kilometre Array-low pathfinder), provides advancements in our capability of probing Galactic magnetism through low-frequency polarimetry. Maps of diffuse polarized radio emission and Faraday rotation can be used to infer properties of, and trace structure in, the magnetic fields in the ISM. However, to date very little of the sky has been probed at high angular and Faraday depth resolution. Read More

2016Nov
Affiliations: 1Oxford, 2Curtin, 3Oxford, 4Alberta, 5Cambridge, 6Cambridge, 7Cambridge, 8Manchester, 9Curtin, Amsterdam, 10Cambridge, 11Cambridge, 12Cambridge, 13Manchester, 14Cambridge, 15AAVSO

The connection between accretion and jet production in accreting white dwarf binary systems, especially dwarf novae, is not well understood. Radio wavelengths provide key insights into the mechanisms responsible for accelerating electrons, including jets and outflows. Here we present densely-sampled radio coverage, obtained with the Arcminute MicroKelvin Imager Large Array, of the dwarf nova SS Cyg during its February 2016 anomalous outburst. Read More

Radio observations of young stellar objects (YSOs) enable the study of ionised plasma outflows from young protostars via their free-free radiation. Previous studies of the low-mass young system T Tau have used radio observations to model the spectrum and estimate important physical properties of the associated ionised plasma (local electron density, ionised gas content and emission measure). However, without an indication of the low-frequency turnover in the free-free spectrum, these properties remain difficult to constrain. Read More

Mergers of galaxy clusters are among the most energetic events in the Universe. These events have significant impact on the intra-cluster medium, depositing vast amounts of energy - often in the form of shocks - as well as heavily influencing the properties of the constituent galaxy population. Many clusters have been shown to host large-scale diffuse radio emission, known variously as radio haloes and relics. Read More

After more than 26 years in quiescence, the black hole transient V404 Cyg went into a luminous outburst in June 2015, and additional activity was detected in late December of the same year. Here, we present an optical spectroscopic follow-up of the December mini-outburst, together with X-ray, optical and radio monitoring that spanned more than a month. Strong flares with gradually increasing intensity are detected in the three spectral ranges during the ~10 days following the Swift trigger. Read More

Standard galaxy formation models predict that large-scale double-lobed radio sources, known as DRAGNs, will always be hosted by elliptical galaxies. In spite of this, in recent years a small number of spiral galaxies have also been found to host such sources. These so-called spiral DRAGNs are still extremely rare, with only $\sim 5$ cases being widely accepted. Read More

(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 sources must contain significant correlated flux density (50-100mJy) at frequencies around 110--190~MHz on scales of a few hundred mas. Read More

We present observations of three active sites of star formation in the Taurus Molecular Cloud complex taken at 323 and 608 MHz (90 and 50 cm, respectively) with the Giant Metrewave Radio Telescope (GMRT). Three pointings were observed as part of a pathfinder project, targeted at the young stellar objects (YSOs) L1551 IRS 5, T Tau and DG Tau (the results for these target sources were presented in a previous paper). In this paper, we search for other YSOs and present a survey comprising of all three fields; a by-product of the large instantaneous field of view of the GMRT. Read More

We present the results of 325 MHz GMRT observations of a super-cluster field, known to contain five Abell clusters at redshift $z \sim 0.2$. We achieve a nominal sensitivity of $34\,\mu$Jy beam$^{-1}$ toward the phase centre. Read More

Cosmic ray electrons (CREs) are a crucial part of the ISM and are observed via synchrotron emission. While much modelling has been carried out on the CRE distribution and propagation of the Milky Way, little has been done on normal external star-forming galaxies. Recent spectral data from a new generation of radio telescopes enable us to find more robust estimations of the CRE propagation. Read More

For a ground-based radio interferometer observing at low frequencies, the ionosphere causes propagation delays and refraction of cosmic radio waves which result in phase errors in the received signal. These phase errors can be corrected using a calibration method that assumes a two-dimensional phase screen at a fixed altitude above the surface of the Earth, known as the thin-layer model. Here we investigate the validity of the thin-layer model and provide a simple equation with which users can check when this approximation can be applied to observations for varying time of day, zenith angle, interferometer latitude, baseline length, ionospheric electron content and observing frequency. Read More

We present the results of a pathfinder project conducted with the Giant Metrewave Radio Telescope (GMRT) to investigate protostellar systems at low radio frequencies. The goal of these investigations is to locate the break in the free-free spectrum where the optical depth equals unity in order to constrain physical parameters of these systems, such as the mass of the ionised gas surrounding these young stars. We detect all three target sources, L1551 IRS 5 (Class I), T Tau and DG Tau (Class II), at frequencies 323 and 608 MHz (wavelengths 90 and 50 cm, respectively). Read More

2016Mar
Authors: S. Buitink1, A. Corstanje2, H. Falcke3, J. R. Hörandel4, T. Huege5, A. Nelles6, J. P. Rachen7, L. Rossetto8, P . Schellart9, O. Scholten10, S. ter Veen11, S. Thoudam12, T. N. G. Trinh13, J. Anderson14, A. Asgekar15, I. M. Avruch16, M. E. Bell17, M. J. Bentum18, G. Bernardi19, P. Best20, A. Bonafede21, F. Breitling22, J. W. Broderick23, W. N. Brouw24, M. Brüggen25, H. R. Butcher26, D. Carbone27, B. Ciardi28, J. E. Conway29, F. de Gasperin30, E. de Geus31, A. Deller32, R. -J. Dettmar33, G. van Diepen34, S. Duscha35, J. Eislöffel36, D. Engels37, J. E. Enriquez38, R. A. Fallows39, R. Fender40, C. Ferrari41, W. Frieswijk42, M. A. Garrett43, J. M. Griessmeier44, A. W. Gunst45, M. P. van Haarlem46, T. E. Hassall47, G. Heald48, J. W. T. Hessels49, M. Hoeft50, A. Horneffer51, M. Iacobelli52, H. Intema53, E. Juette54, A. Karastergiou55, V. I. Kondratiev56, M. Kramer57, M. Kuniyoshi58, G. Kuper59, J. van Leeuwen60, G. M. Loose61, P. Maat62, G. Mann63, S. Markoff64, R. McFadden65, D. McKay-Bukowski66, J. P. McKean67, M. Mevius68, D. D. Mulcahy69, H. Munk70, M. J. Norden71, E. Orru72, H. Paas73, M. Pandey-Pommier74, V. N. Pandey75, M. Pietka76, R. Pizzo77, A. G. Polatidis78, W. Reich79, H. J. A. Röttgering80, A. M. M. Scaife81, D. J. Schwarz82, M. Serylak83, J. Sluman84, O. Smirnov85, B. W. Stappers86, M. Steinmetz87, A. Stewart88, J. Swinbank89, M. Tagger90, Y. Tang91, C. Tasse92, M. C. Toribio93, R. Vermeulen94, C. Vocks95, C. Vogt96, R. J. van Weeren97, R. A. M. J. Wijers98, S. J. Wijnholds99, M. W. Wise100, O. Wucknitz101, S. Yatawatta102, P. Zarka103, J. A. Zensus104
Affiliations: 1Astrophysical Institute, Vrije Universiteit Brussel, 2Department of Astrophysics/IMAPP, Radboud University Nijmegen, 3Department of Astrophysics/IMAPP, Radboud University Nijmegen, 4Department of Astrophysics/IMAPP, Radboud University Nijmegen, 5IKP, Karlsruhe Institute of Technology, 6Department of Astrophysics/IMAPP, Radboud University Nijmegen, 7Department of Astrophysics/IMAPP, Radboud University Nijmegen, 8Department of Astrophysics/IMAPP, Radboud University Nijmegen, 9Department of Astrophysics/IMAPP, Radboud University Nijmegen, 10KVI CART, University of Groningen, 11ASTRON, Netherlands Institute for Radio Astronomy, 12Department of Astrophysics/IMAPP, Radboud University Nijmegen, 13KVI CART, University of Groningen, 14Helmholtz-Zentrum Potsdam, DeutschesGeoForschungsZentrum GFZ, 15ASTRON, Netherlands Institute for Radio Astronomy, 16SRON Netherlands Insitute for Space Research, 17CSIRO Australia Telescope National Facility, 18ASTRON, Netherlands Institute for Radio Astronomy, 19Harvard-Smithsonian Center for Astrophysics, 20Institute for Astronomy, University of Edinburgh, 21University of Hamburg, 22Leibniz-Institut, 23School of Physics and Astronomy, University of Southampton, 24ASTRON, Netherlands Institute for Radio Astronomy, 25University of Hamburg, 26Research School of Astronomy and Astrophysics, Australian National University, 27Anton Pannekoek Institute for Astronomy, University of Amsterdam, 28Max Planck Institute for Astrophysics, 29Onsala Space Observatory, Dept. of Earth and Space Sciences, Chalmers University of Technology, 30University of Hamburg, 31ASTRON, Netherlands Institute for Radio Astronomy, 32ASTRON, Netherlands Institute for Radio Astronomy, 33Astronomisches Institut der Ruhr-Universität Bochum, 34ASTRON, Netherlands Institute for Radio Astronomy, 35ASTRON, Netherlands Institute for Radio Astronomy, 36Thüringer Landessternwarte, 37Hamburger Sternwarte, 38Department of Astrophysics/IMAPP, Radboud University Nijmegen, 39ASTRON, Netherlands Institute for Radio Astronomy, 40Astrophysics, University of Oxford, 41Laboratoire Lagrange, Université Côte d'Azur, 42ASTRON, Netherlands Institute for Radio Astronomy, 43ASTRON, Netherlands Institute for Radio Astronomy, 44LPC2E - Universite d'Orleans/CNRS, 45ASTRON, Netherlands Institute for Radio Astronomy, 46ASTRON, Netherlands Institute for Radio Astronomy, 47School of Physics and Astronomy, University of Southampton, 48ASTRON, Netherlands Institute for Radio Astronomy, 49ASTRON, Netherlands Institute for Radio Astronomy, 50Thüringer Landessternwarte, 51Max-Planck-Institut für Radioastronomie, 52ASTRON, Netherlands Institute for Radio Astronomy, 53Leiden Observatory, Leiden University, 54Astronomisches Institut der Ruhr-Universität Bochum, 55Astrophysics, University of Oxford, 56ASTRON, Netherlands Institute for Radio Astronomy, 57Max-Planck-Institut für Radioastronomie, 58National Astronomical Observatory of Japan, Japan, 59ASTRON, Netherlands Institute for Radio Astronomy, 60ASTRON, Netherlands Institute for Radio Astronomy, 61ASTRON, Netherlands Institute for Radio Astronomy, 62ASTRON, Netherlands Institute for Radio Astronomy, 63Leibniz-Institut, 64Anton Pannekoek Institute for Astronomy, University of Amsterdam, 65ASTRON, Netherlands Institute for Radio Astronomy, 66Sodankylä Geophysical Observatory, University of Oulu, 67ASTRON, Netherlands Institute for Radio Astronomy, 68ASTRON, Netherlands Institute for Radio Astronomy, 69School of Physics and Astronomy, University of Southampton, 70ASTRON, Netherlands Institute for Radio Astronomy, 71ASTRON, Netherlands Institute for Radio Astronomy, 72ASTRON, Netherlands Institute for Radio Astronomy, 73Center for Information Technology, 74Centre de Recherche Astrophysique de Lyon, Observatoire de Lyon, 75ASTRON, Netherlands Institute for Radio Astronomy, 76Astrophysics, University of Oxford, 77ASTRON, Netherlands Institute for Radio Astronomy, 78ASTRON, Netherlands Institute for Radio Astronomy, 79Max-Planck-Institut für Radioastronomie, 80Leiden Observatory, Leiden University, 81School of Physics and Astronomy, University of Southampton, 82Fakultät für Physik, Universität Bielefeld, 83Astrophysics, University of Oxford, 84ASTRON, Netherlands Institute for Radio Astronomy, 85Department of Physics and Electronics, Rhodes University, 86Jodrell Bank Center for Astrophysics, School of Physics and Astronomy, The University of Manchester, 87Leibniz-Institut, 88Astrophysics, University of Oxford, 89Anton Pannekoek Institute for Astronomy, University of Amsterdam, 90LPC2E - Universite d'Orleans/CNRS, 91ASTRON, Netherlands Institute for Radio Astronomy, 92Department of Physics and Electronics, Rhodes University, 93ASTRON, Netherlands Institute for Radio Astronomy, 94ASTRON, Netherlands Institute for Radio Astronomy, 95Leibniz-Institut, 96ASTRON, Netherlands Institute for Radio Astronomy, 97Harvard-Smithsonian Center for Astrophysics, 98Anton Pannekoek Institute for Astronomy, University of Amsterdam, 99ASTRON, Netherlands Institute for Radio Astronomy, 100ASTRON, Netherlands Institute for Radio Astronomy, 101Max-Planck-Institut für Radioastronomie, 102ASTRON, Netherlands Institute for Radio Astronomy, 103LESIA, 104Max-Planck-Institut für Radioastronomie

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 whether this energy range is dominated by Galactic or extragalactic sources. It has also been proposed that the astrophysical neutrino signal comes from accelerators capable of producing cosmic rays of these energies. Read More

We report the discovery of a radio halo in the massive merging cluster MACSJ2243.3-0935, as well as a new radio relic candidate, using the Giant Meterwave Radio Telescope and the KAT-7 telescope. The radio halo is coincident with the cluster X-ray emission and has a largest linear scale of approximately 0. Read More

2015Nov

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 Multifrequency Snapshot Sky Survey (MSSS). The data were recorded between 2011 December and 2012 April and comprised 2149 11-minute snapshots, each covering 175 deg^2. We have found one convincing candidate astrophysical transient, with a duration of a few minutes and a flux density at 60 MHz of 15-25 Jy. Read More

In this analysis we illustrate how the relatively new emission mechanism known as spinning dust can be used to characterize dust grains in the interstellar medium. We demonstrate this by using spinning dust emission observations to constrain the abundance of very small dust grains (a $\lesssim$ 10nm) in a sample of Galactic cold cores. Using the physical properties of the cores in our sample as inputs to a spinning dust model, we predict the expected level of emission at a wavelength of 1cm for four different very small dust grain abundances, which we constrain by comparing to 1cm CARMA observations. Read More

2015Sep
Authors: G. H. Heald, R. F. Pizzo, E. Orrú, R. P. Breton, D. Carbone, C. Ferrari, M. J. Hardcastle, W. Jurusik, G. Macario, D. Mulcahy, D. Rafferty, A. Asgekar, M. Brentjens, R. A. Fallows, W. Frieswijk, M. C. Toribio, B. Adebahr, M. Arts, M. R. Bell, A. Bonafede, J. Bray, J. Broderick, T. Cantwell, P. Carroll, Y. Cendes, A. O. Clarke, J. Croston, S. Daiboo, F. de Gasperin, J. Gregson, J. Harwood, T. Hassall, V. Heesen, A. Horneffer, A. J. van der Horst, M. Iacobelli, V. Jelić, D. Jones, D. Kant, G. Kokotanekov, P. Martin, J. P. McKean, L. K. Morabito, B. Nikiel-Wroczyński, A. Offringa, V. N. Pandey, M. Pandey-Pommier, M. Pietka, L. Pratley, C. Riseley, A. Rowlinson, J. Sabater, A. M. M. Scaife, L. H. A. Scheers, K. Sendlinger, A. Shulevski, M. Sipior, C. Sobey, A. J. Stewart, A. Stroe, J. Swinbank, C. Tasse, J. Trüstedt, E. Varenius, S. van Velzen, N. Vilchez, R. J. van Weeren, S. Wijnholds, W. L. Williams, A. G. de Bruyn, R. Nijboer, M. Wise, A. Alexov, J. Anderson, I. M. Avruch, R. Beck, M. E. Bell, I. van Bemmel, M. J. Bentum, G. Bernardi, P. Best, F. Breitling, W. N. Brouw, M. Brüggen, H. R. Butcher, B. Ciardi, J. E. Conway, E. de Geus, A. de Jong, M. de Vos, A. Deller, R. J. Dettmar, S. Duscha, J. Eislöffel, D. Engels, H. Falcke, R. Fender, M. A. Garrett, J. Grießmeier, A. W. Gunst, J. P. Hamaker, J. W. T. Hessels, M. Hoeft, J. Hörandel, H. A. Holties, H. Intema, N. J. Jackson, E. Jütte, A. Karastergiou, W. F. A. Klijn, V. I. Kondratiev, L. V. E. Koopmans, M. Kuniyoshi, G. Kuper, C. Law, J. van Leeuwen, M. Loose, P. Maat, S. Markoff, R. McFadden, D. McKay-Bukowski, M. Mevius, J. C. A. Miller-Jones, R. Morganti, H. Munk, A. Nelles, J. E. Noordam, M. J. Norden, H. Paas, A. G. Polatidis, W. Reich, A. Renting, H. Röttgering, A. Schoenmakers, D. Schwarz, J. Sluman, O. Smirnov, B. W. Stappers, M. Steinmetz, M. Tagger, Y. Tang, S. ter Veen, S. Thoudam, R. Vermeulen, C. Vocks, C. Vogt, R. A. M. J. Wijers, O. Wucknitz, S. Yatawatta, P. Zarka

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 design of the survey. Compared to previous radio surveys, MSSS is exceptional due to its intrinsic multifrequency nature providing information about the spectral properties of the detected sources over more than two octaves (from 30 to 160 MHz). Read More

The Arcminute Microkelvin Imager Galactic Plane Survey (AMIGPS) provides mJy-sensitivity, arcminute-resolution interferometric images of the northern Galactic plane at $\approx$ 16 GHz. The first data release covered $76^{\circ} \lessapprox \ell \lessapprox 170^{\circ}$ between latitudes of $|b| \lessapprox 5^{\circ}$; here we present a second data release, extending the coverage to $53^{\circ} \lessapprox \ell \lessapprox 193^{\circ}$ and including high-latitude extensions to cover the Taurus and California giant molecular cloud regions, and the recently discovered large supernova remnant G159.6+7. Read More

We present the first search for spinning dust emission from a sample of 34 Galactic cold cores, performed using the CARMA interferometer. For each of our cores we use photometric data from the Herschel Space Observatory to constrain N_{H}, T_{d}, n_{H}, and G_{0}. By computing the mass of the cores and comparing it to the Bonnor-Ebert mass, we determined that 29 of the 34 cores are gravitationally unstable and undergoing collapse. Read More

We know that magnetic fields are pervasive across all scales in the Universe and over all of cosmic time and yet our understanding of many of the properties of magnetic fields is still limited. We do not yet know when, where or how the first magnetic fields in the Universe were formed, nor do we fully understand their role in fundamental processes such as galaxy formation or cosmic ray acceleration or how they influence the evolution of astrophysical objects. The greatest challenge to addressing these issues has been a lack of deep, broad bandwidth polarimetric data over large areas of the sky. Read More

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. Studying pulsars like PSR B0823+26 provides further insight into the relationship between these various emission phenomena and what they might teach us about pulsar magnetospheres. Read More

We report the presence of high significance diffuse radio emission from the Triangulum Australis cluster using observations made with the KAT-7 telescope and propose that this emission is a giant radio halo. We compare the radio power from this proposed halo with X-ray and SZ measurements and demonstrate that it is consistent with the established scaling relations for cluster haloes. By combining the X-ray and SZ data we calculate the ratio of non-thermal to thermal electron pressure within Triangulum Australis to be $X=0. Read More

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 emission to large scales in the complex source 4C 35.06 located in the core of the galaxy cluster Abell 407. At higher spatial resolution (~4"), the source was known to have two inner radio lobes spanning 31 kpc and a diffuse, low-brightness extension running parallel to them, offset by about 11 kpc (in projection). Read More

We propose a new multiscale method to calculate the amplitude of the gradient of the linear polarisation vector using a wavelet-based formalism. We demonstrate this method using a field of the Canadian Galactic Plane Survey (CGPS) and show that the filamentary structure typically seen in gradients of linear polarisation maps depends strongly on the instrumental resolution. Our analysis reveals that different networks of filaments are present on different angular scales. Read More

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 radically different from those measured during fair-weather conditions. With the use of a simple two-layer model for the atmospheric electric field, these patterns can be well reproduced by state-of-the-art simulation codes. Read More

Predictability estimates of ensemble prediction systems are uncertain due to limited numbers of past forecasts and observations. To account for such uncertainty, this paper proposes a Bayesian inferential framework that provides a simple 6-parameter representation of ensemble forecasting systems and the corresponding observations. The framework is probabilistic, and thus allows for quantifying uncertainty in predictability measures such as correlation skill and signal-to-noise ratios. Read More

Deep surveys with the SKA1-MID array offer for the first time the opportunity to systematically explore the polarization properties of the microJy source population. Our knowledge of the polarized sky approaching these levels is still very limited. In total intensity the population will be dominated by star-forming and normal galaxies to intermediate redshifts ($z \sim1-2$), and low-luminosity AGN to high redshift. Read More

Magnetic fields play an important role in shaping the structure and evolution of the interstellar medium (ISM) of galaxies, but the details of this relationship remain unclear. With SKA1, the 3D structure of galactic magnetic fields and its connection to star formation will be revealed. A highly sensitive probe of the internal structure of the magnetoionized ISM is the partial depolarization of synchrotron radiation from inside the volume. Read More

Magnetic fields in the Milky Way are present on a wide variety of sizes and strengths, influencing many processes in the Galactic ecosystem such as star formation, gas dynamics, jets, and evolution of supernova remnants or pulsar wind nebulae. Observation methods are complex and indirect; the most used of these are a grid of rotation measures of unresolved polarized extragalactic sources, and broadband polarimetry of diffuse emission. Current studies of magnetic fields in the Milky Way reveal a global spiral magnetic field with a significant turbulent component; the limited sample of magnetic field measurements in discrete objects such as supernova remnants and HII regions shows a wide variety in field configurations; a few detections of magnetic fields in Young Stellar Object jets have been published; and the magnetic field structure in the Galactic Center is still under debate. Read More

We investigate the possibility for the SKA to detect and study the magnetic fields in galaxy clusters and in the less dense environments surrounding them using Faraday Rotation Measures. To this end, we produce 3-dimensional magnetic field models for galaxy clusters of different masses and in different stages of their evolution, and derive mock rotation measure observations of background radiogalaxies. According to our results, already in phase I, we will be able to infer the magnetic field properties in galaxy clusters as a function of the cluster mass, down to $10^{13}$ solar-masses. Read More

Studying galaxy clusters through their Sunyaev-Zel'dovich (SZ) imprint on the Cosmic Microwave Background has many important advantages. The total SZ signal is an accurate and precise tracer of the total pressure in the intra-cluster medium and of cluster mass, the key observable for using clusters as cosmological probes. Band 5 observations with SKA-MID towards cluster surveys from the next generation of X-ray telescopes such as e-ROSITA and from Euclid will provide the robust mass estimates required to exploit these samples. Read More

In this chapter, we will outline the scientific motivation for studying Anomalous Microwave Emission (AME) with the SKA. AME is thought to be due to electric dipole radiation from small spinning dust grains, although thermal fluctuations of magnetic dust grains may also contribute. Studies of this mysterious component would shed light on the emission mechanism, which then opens up a new window onto the interstellar medium (ISM). Read More

Abell 3667 is among the most well-studied galaxy clusters in the Southern Hemisphere. It is known to host two giant radio relics and a head-tail radio galaxy as the brightest cluster galaxy. Recent work has suggested the additional presence of a bridge of diffuse synchrotron emission connecting the North-Western radio relic with the cluster centre. Read More

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 time compression effects lead to a ring of amplified emission which starts to dominate the emission pattern for frequencies above ~100 MHz. In this article we present the first detailed measurements of this structure. Read More

Carbon radio recombination lines (RRLs) at low frequencies (<=500 MHz) trace the cold, diffuse phase of the interstellar medium, which is otherwise difficult to observe. We present the detection of carbon RRLs in absorption in M82 with LOFAR in the frequency range of 48-64 MHz. This is the first extragalactic detection of RRLs from a species other than hydrogen, and below 1 GHz. Read More

2014Sep

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$^{-1}$, making them the deepest images ever obtained in this frequency range. In total, we detect between 300 and 400 sources in each of these images, covering an area of 17 to 52 deg$^{2}$. Read More

2014Sep
Affiliations: 1SIfA, 2U. Minnesota, 3SIfA, 4SIfA, 5MPA, 6U. Southampton, 7SIfA, 8U. Nagoya, 9U. Nagoya, 10U. Minnesota, 11SIfA, 12U. Southampton, 13ICMM, 14U. Calgary, 15U. Kumamoto, 16CfA, 17U. Calgary

(abridged) We run a Faraday structure determination data challenge to benchmark the currently available algorithms including Faraday synthesis (previously called RM synthesis in the literature), wavelet, compressive sampling and $QU$-fitting. The frequency set is similar to POSSUM/GALFACTS with a 300 MHz bandwidth from 1.1 to 1. Read More

Synchrotron emission has recently been detected in the jet of a massive protostar, providing further evidence that certain jet formation characteristics for young stars are similar to those found for highly relativistic jets from AGN. We present data at 325 and 610 MHz taken with the GMRT of the young, low-mass star DG Tau, an analog of the Sun soon after its birth. This is the first investigation of a low-mass YSO at at such low frequencies. Read More

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 burst limit and the discovery of two new pulsars. The first survey, the LOFAR Pilot Pulsar Survey (LPPS), observed a large fraction of the northern sky, ~1.4 x 10^4 sq. Read More

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 (<100 MHz), the Sun has not been imaged extensively because of the instrumental limitations of previous radio telescopes. Here, the combined high spatial, spectral and temporal resolution of the Low Frequency Array (LOFAR) was used to study solar Type III radio bursts at 30-90 MHz and their association with CMEs. Read More

2014Jul

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 from the Low-Frequency Array - Epoch of Reionization (LOFAR-EoR) data. We use the high band antennas of LOFAR to image this region and RM-synthesis to unravel structures of polarized emission at high Galactic latitudes. The brightness temperature of the detected Galactic emission is on average 4 K in polarized intensity and covers the range from -10 to +13rad m^-2 in Faraday depth. Read More

The grand-design spiral galaxy M51 was observed with the LOFAR High Frequency Antennas (HBA) and imaged in total intensity and polarisation. This observation covered the frequencies between 115 MHz and 175 MHz. We produced an image of total emission of M51 at the mean frequency of 151 MHz with 20 arcsec resolution and 0. Read More

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 emission comes from a finite distance of a few kilometers, the incident wavefront is non-planar. A spherical, conical or hyperbolic shape of the wavefront has been proposed, but measurements of individual air showers have been inconclusive so far. Read More

2014Mar
Affiliations: 1U. Southampton, 2U. Amsterdam, 3U. Southampton, 4U. Southampton, 5U. Amsterdam, 6U. Southampton, 7U. Cambridge, 8U. Cambridge, 9U. Amsterdam, 10U. Cambridge

We present one of the best sampled early time light curves of a gamma-ray burst (GRB) at radio wavelengths. Using the Arcminute Mircrokelvin Imager (AMI) we observed GRB 130427A at the central frequency of 15.7 GHz between 0. Read More

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 the 33 to 57 MHz range. These low frequency radio observations provide us with a new line of sight to study the diffuse, neutral gas in our Galaxy. Read More

2014Jan

We outline the science case for extended radio emission and polarization in galaxy clusters which would be a scientifically important area of research for an upcoming Jansky Very Large Array Sky Survey. The survey would provide a major contribution in three key areas of the physics of clusters: 1) the active galactic nucleus population and the impact of feedback on the evolution of the intra-cluster medium, 2) the origin and evolution of diffuse cluster radio sources to probe the physics of mergers with implications for cosmology, and 3) the origin and role of magnetic fields in the ICM and in large scale structures. Considering all three areas, a survey must have sufficient spatial resolution to study the tailed galaxies which trace the cluster weather as well as the radio lobes driving energy into the cluster from the central AGN. Read More

We outline the prospects for performing pioneering radio weak gravitational lensing analyses using observations from a potential forthcoming JVLA Sky Survey program. A large-scale survey with the JVLA can offer interesting and unique opportunities for performing weak lensing studies in the radio band, a field which has until now been the preserve of optical telescopes. In particular, the JVLA has the capacity for large, deep radio surveys with relatively high angular resolution, which are the key characteristics required for a successful weak lensing study. Read More