The LOFAR long baseline snapshot calibrator survey

Moldón, J.; Deller, Adam T.; Wucknitz, O.; Jackson, N.; Drabent, A.; Carozzi, T. D.; Conway, J.; Kapińska, A. D.; McKean, J. P.; Morabito, L. K.; Varenius, Eskil; Zarka, Philippe; Anderson, J. M.; Asgekar, A.; Avruch, I. M.; Bell, M. E.; Bentum, Marinus Jan; Bernardi, G.; Best, P. N.; Bîrzan, L.; Bregman, J. D.; Breitling, F.; Broderick, J. W.; Brüggen, M.; Butcher, H. R.; Carbone, D.; Ciardi, B.; Gasperin, F. de; Geus, E. de; Duscha, S.; Eislöffel, J.; Engels, D.; Falcke, H.; Fallows, R. A.; Fender, R. P.; Ferrari, C.; Frieswijk, W.; Garrett, M. A.; Grießmeier, J.-M.; Gunst, A. W.; Hamaker, J. P.; Hassall, T. E.; Heald, G.; Hoeft, M.; Juette, E.; Karastergiou, A.; Kondratiev, V. I.; Krämer, M.; Kuniyoshi, M.; Küper, G.; Maat, P.; Mann, G.; Markoff, Sera; McFadden, R.; McKay-Bukowski, D.; Morganti, Raffaella; Munk, H.; Norden, M. J.; Offringa, A. R.; Orrù, E.; Paas, H.; Pandey-Pommier, M.; Pizzo, R.; Polatidis, A. G.; Reich, W.; Röttgering, H. J. A.; Rowlinson, A.; Scaife, A.; Schwarz, Dominik J.; Sluman, J.; Smirnov, O.; Stappers, B. W.; Steinmetz, Matthias; Tagger, M.; Tang, Y.; Tasse, C.; Thoudam, Satyendra; Toribio, M. C.; Vermeulen, R. C.; Vocks, C.; Weeren, R. J. van; White, S. M.; Wise, Michael; Yatawatta, S.; Zensus, J. A.

doi:10.1051/0004-6361/201425042

Cited by 26 publications

(11 citation statements)

References 22 publications

(23 reference statements)

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“…The ionospheric delay is by far the dominant effect. For a more indepth discussion of all the different contributions to the delay at 150 MHz for LOFAR, see Moldón et al (2015). The delay fitting-task FRING in AIPS fits a single, non-dispersive delay solution to each so-called intermediate frequency (IF), where an IF is a continuous bandwidth segment.…”

Section: Calibrator Residual Phase Delay and Ratementioning

confidence: 99%

LOFAR VLBI studies at 55 MHz of 4C 43.15, az= 2.4 radio galaxy

Morabito¹,

Deller²,

Röttgering³

et al. 2016

Mon. Not. R. Astron. Soc.

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The correlation between radio spectral index and redshift has been exploited to discover high redshift radio galaxies, but its underlying cause is unclear. It is crucial to characterise the particle acceleration and loss mechanisms in high redshift radio galaxies to understand why their radio spectral indices are steeper than their local counterparts. Low frequency information on scales of ∼ 1 arcsec are necessary to determine the internal spectral index variation. In this paper we present the first spatially resolved studies at frequencies below 100 MHz of the z = 2.4 radio galaxy 4C 43.15 which was selected based on its ultra-steep spectral index (α < −1; S ν ∼ ν α ) between 365 MHz and 1.4 GHz. Using the International Low Frequency Array (LO-FAR) Low Band Antenna we achieve sub-arcsecond imaging resolution at 55 MHz with VLBI techniques. Our study reveals low-frequency radio emission extended along the jet axis, which connects the two lobes. The integrated spectral index for frequencies < 500 MHz is -0.83. The lobes have integrated spectral indices of -1.31±0.03 and -1.75±0.01 for frequencies ≥ 1.4 GHz, implying a break frequency between 500 MHz and 1.4 GHz. These spectral properties are similar to those of local radio galaxies. We conclude that the initially measured ultra-steep spectral index is due to a combination of the steepening spectrum at high frequencies with a break at intermediate frequencies.

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Section: Calibrator Residual Phase Delay and Ratementioning

confidence: 99%

LOFAR VLBI studies at 55 MHz of 4C 43.15, az= 2.4 radio galaxy

Morabito¹,

Deller²,

Röttgering³

et al. 2016

Mon. Not. R. Astron. Soc.

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“…Motivated by the importance of obtaining low radio frequency observations for extragalactic radio sources here we present the results of LOFAR observations of a quasar jet in 4C +19.44. By using the international baselines of the LOFAR (van Haarlem et al 2013;Moldón et al 2015;Varenius et al 2016;Morabito et al 2016) we have been able to reach a resolution at ∼ 0.4 arcsec at 150 MHz, thus matching the resolution of available JVLA observations at 5 GHz (Harris et al 2017). These observations allowed us to resolve, spatially, the quasar jet in 4C+19.44, highlighting the knotty structure at these wavelengths.…”

Section: Introductionmentioning

confidence: 61%

LOFAR Observations of 4C+19.44: On the Discovery of Low-frequency Spectral Curvature in Relativistic Jet Knots

Harris

Moldón

Oonk

et al. 2019

ApJ

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We present the first LOFAR observations of the radio jet in the quasar 4C+19.44 (a.k.a. PKS 1354+19) obtained with the long baselines. The achieved resolution is very well matched to that of archival Jansky Very Large Array (JVLA) observations at higher radio frequencies as well as the archival X-ray images obtained with Chandra. We found that, for several knots along the jet, the radio flux densities measured at hundreds of MHz lie well below the values estimated by extrapolating the GHz spectra. This clearly indicates the presence of spectral curvature. Radio spectral curvature has been already observed in different source classes and/or extended radio structures and it has been often interpreted as due to intrinsic processes, as a curved particle energy distribution, rather than absorption mechanisms ( Razin-Tsytovich effect, free-free or synchrotron self absorption to name a few). Here we discuss our results according to the scenario where particles undergo stochastic acceleration mechanisms also in quasar jet knots.

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“…Nonetheless, targeted VLBI surveys have been shown to be feasible at metric wavelengths. Moldón et al (2015) surveyed 630 carefully selected sources in two hours with International LOFAR at 140 MHz. From their detection rate, they estimated that there is one suitable primary calibrator per square degree of sky.…”

Section: Implications For Astrophysical Studiesmentioning

confidence: 99%

Interplanetary Scintillation with the Murchison Widefield Array I: a sub-arcsecond survey over 900 deg2 at 79 and 158 MHz

Morgan

Macquart

Ekers

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We present the first dedicated observations of Interplanetary Scintillation (IPS) with the Murchison Widefield Array (MWA). We have developed a synthesis imaging technique, tailored to the properties of modern "large-N" low-frequency radio telescopes. This allows us to image the variability on IPS timescales across 900 square degrees simultaneously. We show that for our observations, a sampling rate of just 2 Hz is sufficient to resolve the IPS signature of most sources. We develop tests to ensure that IPS variability is separated from ionospheric or instrumental variability. We validate our results by comparison with existing catalogues of IPS sources, and nearcontemporaneous observations by other IPS facilities. Using just five minutes of data, we produce catalogues at both 79 MHz and 158 MHz, each containing over 350 scintillating sources. At the field centre we detect approximately one scintillating source per square degree, with a minimum scintillating flux density at 158 MHz of 110 mJy, corresponding to a compact flux density of approximately 400 mJy. Each of these sources is a known radio source, however only a minority were previously known to contain sub-arcsecond components. We discuss our findings and the prospects they hold for future astrophysical and heliospheric studies.

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The LOFAR long baseline snapshot calibrator survey

Cited by 26 publications

References 22 publications

LOFAR VLBI studies at 55 MHz of 4C 43.15, az= 2.4 radio galaxy

LOFAR VLBI studies at 55 MHz of 4C 43.15, az= 2.4 radio galaxy

LOFAR Observations of 4C+19.44: On the Discovery of Low-frequency Spectral Curvature in Relativistic Jet Knots

Interplanetary Scintillation with the Murchison Widefield Array I: a sub-arcsecond survey over 900 deg2 at 79 and 158 MHz

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