Observations of 44 extragalactic radio sources  with the VLBA at 92 cm

Rampadarath, H.; Garrett, M. A.; Polatidis, A. G.

doi:10.1051/0004-6361/200911802

Cited by 6 publications

(5 citation statements)

References 16 publications

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“…So far only a handful of works based on VLBI images at 327 MHz are available. They mainly focus on variable extragalactic sources (Altschuler et al 1995;Chuprikov et al 1999;Rampadarath, Garrett & Polatidis 2009) or on deep wide field VLBI survey (Lenc et al 2008). The data presented here are the deepest and with the highest angular resolution at 327 MHz for a sample of CSS/GPS published so far.…”

Section: Datementioning

confidence: 99%

VLBI images at 327 MHz of compact steep spectrum and GHz-peaked spectrum sources from the 3C and PW samples

Dallacasa

Orienti

Fanti

et al. 2021

Monthly Notices of the Royal Astronomical Society

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We present results on global very long baseline interferometry (VLBI) observations at 327 MHz of eighteen compact steep-spectrum (CSS) and GHz-peaked spectrum (GPS) radio sources from the 3C and the Peacock & Wall catalogues. About 80 per cent of the sources have a ’double/triple’ structure. The radio emission at 327 MHz is dominated by steep-spectrum extended structures, while compact regions become predominant at higher frequencies. As a consequence, we could unambiguously detect the core region only in three sources, likely due to self-absorption affecting its emission at this low frequency. Despite their low surface brightness, lobes store the majority of the source energy budget, whose correct estimate is a key ingredient in tackling the radio source evolution. Low-frequency VLBI observations able to disentangle the lobe emission from that of other regions are therefore the best way to infer the energetics of these objects. Dynamical ages estimated from energy budget arguments provide values between 2× 103 and 5× 104 yr, in agreement with the radiative ages estimated from the fit of the integrated synchrotron spectrum, further supporting the youth of these objects. A discrepancy between radiative and dynamical ages is observed in a few sources where the integrated spectrum is dominated by hotspots. In this case the radiative age likely represents the time spent by the particles in these regions, rather than the source age.

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Section: Datementioning

confidence: 99%

VLBI images at 327 MHz of compact steep spectrum and GHz-peaked spectrum sources from the 3C and PW samples

Dallacasa

Orienti

Fanti

et al. 2021

Monthly Notices of the Royal Astronomical Society

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“…Later, Wucknitz (2010a) applied an efficient wide-field mapping method to image the entire primary beam for one of the fields, finding exactly the same sources. Rampadarath et al (2009) analysed archival Very Long Baseline Array (VLBA) observations of 43 sources at 325 MHz, finding 30 which would be satisfactory calibrators for International LOFAR observations, but were not able to draw any conclusions about the density of satisfactory calibrators in general.…”

Section: Introductionmentioning

confidence: 99%

The LOFAR long baseline snapshot calibrator survey

Moldón¹,

Deller²,

Wucknitz³

et al. 2015

Proceedings of 12th European VLBI Network Symposium and Users Meeting — PoS(EVN 2014)

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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 subarcsecond observations at 140 MHz. Methods. We used the multi-beaming capability of LOFAR to conduct a fast and computationally inexpensive survey with the full International LOFAR array. Sources were pre-selected on the basis of 325 MHz arcminute-scale flux density using existing catalogues. By observing 30 different sources in each of the 12 sets of pointings per hour, we were able to inspect 630 sources in two hours to determine if they possess a sufficiently bright compact component to be usable as LOFAR delay calibrators. Results. Over 40% of the observed sources are detected on multiple baselines between international stations and 86 are classified as satisfactory calibrators. We show that a flat low-frequency spectrum (from 74 to 325 MHz) is the best predictor of compactness at 140 MHz. We extrapolate from our sample to show that the density of calibrators on the sky that are sufficiently bright to calibrate dispersive and non-dispersive delays for the International LOFAR using existing methods is 1.0 per square degree. Conclusions. The observed density of satisfactory delay calibrator sources means that observations with International LOFAR should be possible at virtually any point in the sky, provided that a fast and efficient search using the methodology described here is conducted prior to the observation to identify the best calibrator.

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“…So far only a handful of works based on VLBI images at 327 MHz are available. They mainly focus on variable extragalactic sources (Altschuler et al 1995;Chuprikov et al 1999;Rampadarath et al 2009) or on deep wide field VLBI survey (Lenc et al 2008). The data presented here are the deepest and with the highest angular resolution at 327 MHz for a sample of CSS/GPS published so far.…”

Section: Introductionmentioning

confidence: 99%

VLBI images at 327 MHz of compact steep spectrum and GHz-peaked spectrum sources from the 3C and PW samples

Dallacasa,

Orienti,

Fanti

et al. 2021

Preprint

View full text Add to dashboard Cite

We present results on global very long baseline interferometry (VLBI) observations at 327 MHz of eighteen compact steep-spectrum (CSS) and GHz-peaked spectrum (GPS) radio sources from the 3C and the Peacock & Wall catalogues. About 80 per cent of the sources have a 'double/triple' structure. The radio emission at 327 MHz is dominated by steep-spectrum extended structures, while compact regions become predominant at higher frequencies. As a consequence, we could unambiguously detect the core region only in three sources, likely due to self-absorption affecting its emission at this low frequency. Despite their low surface brightness, lobes store the majority of the source energy budget, whose correct estimate is a key ingredient in tackling the radio source evolution. Low-frequency VLBI observations able to disentangle the lobe emission from that of other regions are therefore the best way to infer the energetics of these objects. Dynamical ages estimated from energy budget arguments provide values between 2×10 3 and 5×10 4 yr, in agreement with the radiative ages estimated from the fit of the integrated synchrotron spectrum, further supporting the youth of these objects. A discrepancy between radiative and dynamical ages is observed in a few sources where the integrated spectrum is dominated by hotspots. In this case the radiative age likely represents the time spent by the particles in these regions, rather than the source age.

show abstract

Observations of 44 extragalactic radio sources with the VLBA at 92 cm

Cited by 6 publications

References 16 publications

VLBI images at 327 MHz of compact steep spectrum and GHz-peaked spectrum sources from the 3C and PW samples

VLBI images at 327 MHz of compact steep spectrum and GHz-peaked spectrum sources from the 3C and PW samples

The LOFAR long baseline snapshot calibrator survey

VLBI images at 327 MHz of compact steep spectrum and GHz-peaked spectrum sources from the 3C and PW samples

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