Faceting for direction-dependent spectral deconvolution

Tasse, C.; Hugo, B.; Mirmont, M.; Smirnov, O.; Atemkeng, Marcellin; Bester, L.; Hardcastle, M. J.; Lakhoo, R.; Perkins, Simon; Shimwell, T. W.

doi:10.1051/0004-6361/201731474

Cited by 263 publications

(249 citation statements)

References 26 publications

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“…5.1). This pipeline makes use of kMS (Tasse 2014 andSmirnov &Tasse 2015) for DD calibration, and DDFacet (Tasse et al 2018) is used to apply the DD calibration solutions during the imaging. After completion of the LoTSS data processing pipeline a post processing step is conducted to subtract all the sources besides the targets and calibrate in the directions of the targets.…”

Section: Gmrt Data Reductionmentioning

confidence: 99%

Revived fossil plasma sources in galaxy clusters

Mandal

Intema

Weeren

et al. 2020

A&A

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It is well established that particle acceleration by shocks and turbulence in the intra-cluster medium can produce cluster-scale synchrotron emitting sources. However, the detailed physics of these particle acceleration processes is still not well understood. One of the main open questions is the role of fossil relativistic electrons that have been deposited in the intra-cluster medium by radio galaxies. These synchrotron-emitting electrons are very difficult to study, as their radiative life time is only tens of Myrs at GHz frequencies, and are therefore a relatively unexplored population. Despite the typical steep radio spectrum due to synchrotron losses, these fossil electrons are barely visible even at radio frequencies well below a GHz. However, when a pocket of fossil radio plasma is compressed, it boosts the visibility at sub-GHz frequencies, creating so-called radio phoenices. This compression can be the result of bulk motion and shocks in the ICM due to merger activity. In this paper, we demonstrate the discovery potential of low frequency radio sky surveys to find and study revived fossil plasma sources in galaxy clusters. We used the 150 MHz TGSS and 1.4 GHz NVSS sky surveys to identify candidate radio phoenices. A subset of three candidates were studied in detail using deep multi-band radio observations (LOFAR and GMRT), X-ray (Chandra or XMM-Newton) and archival optical observations. Two of the three sources are new discoveries. Using these observations, we identified common observational properties (radio morphology, ultra-steep spectrum, X-ray luminosity, dynamical state) that will enable us to identify this class of sources more easily, and helps to understand the physical origin of these sources.

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Section: Gmrt Data Reductionmentioning

confidence: 99%

Revived fossil plasma sources in galaxy clusters

Mandal

Intema

Weeren

et al. 2020

A&A

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“…Aftewards, the calibration scheme and pipelines developed for LoTSS were applied (see Shimwell et al 2019 for more details). In particular, the PREFACTOR pipeline Williams et al 2016) and version v2.2-167 of the DDFacet pipeline 1 (see Tasse et al 2018;Tasse et al in prep. ) were used to perform direction-independent and dependent calibration, respectively, using the default parameters.…”

Section: Lofar Observations At 144 Mhz and Data Reductionmentioning

confidence: 99%

Radio spectral properties and jet duty cycle in the restarted radio galaxy 3C388

Brienza

Morganti

Harwood

et al. 2020

A&A

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Context. Restarted radio galaxies represent a unique tool for investigating the duty cycle of the jet activity in active galactic nuclei (AGN). The radio galaxy 3C388 has long been claimed to be a peculiar example of an AGN with multi-epoch activity because it shows a very sharp discontinuity in the GHz spectral index distribution of its lobes. Aims. We present here for the first time a spatially resolved study of the radio spectrum of 3C388 down to MHz frequencies aimed at investigating the radiative age of the source and constraining its duty cycle. Methods. We used new low-frequency observations at 144 MHz performed with the Low Frequency Array and at 350 MHz performed with the Very Large Array that we combined with archival data at higher frequencies (614, 1400, and 4850 MHz).Results. We find that the spectral indices in the lower frequency range, 144-614 MHz, have flatter values (α low ∼0.55-1.14) than those observed in the higher frequency range, 1400-4850 MHz, (α high ∼0.75-1.57), but they follow the same distribution across the lobes, with a systematic steepening towards the edges. However, the spectral shape throughout the source is not uniform and often deviates from standard models. This suggests that mixing of different particle populations occurs, although it remains difficult to understand whether this is caused by observational limitations (insufficient spatial resolution and/or projection effects) or by the intrinsic presence of multiple particle populations, which might be related to the two different outbursts.Conclusions. Using single-injection radiative models, we compute that the total source age is 80 Myr and that the duty cycle is about t on /t tot ∼ 60%, which is enough to prevent the intracluster medium from cooling, according to X-ray estimates. While to date the radio spectral distribution of 3C388 remains a rare case among radio galaxies, multi-frequency surveys performed with new-generation instruments will soon allow us to investigate whether more sources with the same characteristics exist.

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“…A detailed description of the procedure, which was developed for the LOFAR Two-metre Sky Survey (LoTSS), can be found in Shimwell et al (2017Shimwell et al ( , 2019. The direction-independent pipeline removed the effects outlined in de Gasperin et al (2019) The direction-dependent step made use of kms (Tasse 2014a,b;Smirnov & Tasse 2015) and ddfacet (Tasse et al 2018) for calibration and imaging, respectively. 3 The calibrated data per 2-h observation comprised 25 blocks of 10 sub-bands each; the highest-frequency block had four empty sub-bands because we used 246 sub-bands in total.…”

Section: Lofar Observations and Data Reductionmentioning

confidence: 99%

LOFAR 144-MHz follow-up observations of GW170817

Broderick

Shimwell

Gourdji

et al. 2020

Monthly Notices of the Royal Astronomical Society

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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 Advanced LIGO-Virgo. These data, with a central frequency of 144 MHz, were obtained with LOFAR, the Low-Frequency Array. The maximum elevation of the target is just 13. • 7 when observed with LOFAR, making our observations particularly challenging to calibrate and significantly limiting the achievable sensitivity. On timescales of 130-138 and 371-374 days after the merger event, we obtain 3σ upper limits for the afterglow component of 6.6 and 19.5 mJy beam −1 , respectively. Using our best upper limit and previously published, contemporaneous higher-frequency radio data, we place a limit on any potential steepening of the radio spectrum between 610 and 144 MHz: the two-point spectral index α 610 144 −2.5. We also show that LOFAR can detect the afterglows of future binary neutron star merger events occurring at more favourable elevations.

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Faceting for direction-dependent spectral deconvolution

Cited by 263 publications

References 26 publications

Revived fossil plasma sources in galaxy clusters

Revived fossil plasma sources in galaxy clusters

Radio spectral properties and jet duty cycle in the restarted radio galaxy 3C388

LOFAR 144-MHz follow-up observations of GW170817

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