Recent LOFAR imaging pipeline results

Heald, G.; McKean, J. P.; Pizzo, R.; Diepen, Ger van; Zwieten, J. E. van; Weeren, R. J. van; Rafferty, D. A.; Tol, S. van der; Bîrzan, L.; Shulevski, Aleksandar; Swinbank, J.; Orrù, E.; Gasperin, F. de; Ker, L. M.; Bonafede, A.; Macario, G.; Ferrari, Chiara

doi:10.22323/1.112.0057

Cited by 24 publications

(23 citation statements)

References 11 publications

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“…The station beams are complex valued, time, frequency and direction dependent, and are not the same for all of the stations. The data were pre-processed by the observatory pipeline (Heald et al 2010) as described below. Each SB was automatically flagged for radio frequency interference (RFI) using the AOFlagger (Offringa et al 2012), and then averaged in time to 10 seconds per sample and in frequency by a factor of 16, making the frequency resolution of the output data 4 channels / SB.…”

Section: Observations and Data Reductionmentioning

confidence: 99%

Radiative age mapping of the remnant radio galaxy B2 0924+30: the LOFAR perspective

Shulevski

Morganti

Harwood

et al. 2017

A&A

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We have observed the steep spectrum radio source B2 0924+30 using the LOw Frequency ARray (LOFAR) telescope. Hosted by a z=0.026 elliptical galaxy, it has a relatively large angular size of 12 (corresponding to 360 kpc projected linear size) and a morphology reminiscent of a remnant Fanaroff-Riley type II (FRII) radio galaxy. Studying active galactic nuclei (AGN) radio remnants can give us insight into the time-scales involved into the episodic gas accretion by AGNs and their dependence on the AGN host environment. The proximity of the radio galaxy allows us to make detailed studies of its radio structure and map its spectral index and radiative age distribution. We combine LOFAR and archival images to study the spectral properties at a spatial resolution of 1 . We derive low frequency spectral index maps and use synchrotron ageing models to infer ages for different regions of the source. Thus, we are able to extend the spectral ageing studies into a hitherto unexplored frequency band, adding more robustness to our results. Our detailed spectral index mapping, while agreeing with earlier lower resolution studies, shows flattening of the spectral index towards the outer edges of the lobes. The spectral index of the lobes is α 609 140 ∼ −1 and gradually steepens to α 609 140 ∼ −1.8 moving towards the inner edges of the lobes. Using radiative ageing model fitting we show that the AGN activity ceased around 50 Myr ago. We note that the outer regions of the lobes are younger than the inner regions which is interpreted as a sign that those regions are remnant hotspots. We demonstrate the usefulness of maps of AGN radio remnants taken at low frequencies and suggest caution over the interpretation of spectral ages derived from integrated flux density measurements versus age mapping. The spectral index properties as well as the derived ages of B2 0924+30 are consistent with it being an FRII AGN radio remnant. LOFAR data are proving to be instrumental in extending our studies to the lowest radio frequencies and enabling analysis of the oldest source regions.

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Section: Observations and Data Reductionmentioning

confidence: 99%

Radiative age mapping of the remnant radio galaxy B2 0924+30: the LOFAR perspective

Shulevski

Morganti

Harwood

et al. 2017

A&A

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“…The MSSS commissioning project has driven the development of the first version of the standard imaging pipeline (SIP; Heald et al 2010), which can be scheduled by the control system to run automatically on the central processing cluster upon completion of the individual observations. The SIP embodies the calibration strategy described in this section, and is now being upgraded to allow improved image quality at higher angular resolution.…”

Section: Calibration and Imaging Strategymentioning

confidence: 99%

The LOFAR Multifrequency Snapshot Sky Survey (MSSS)

Heald

Pizzo

Orrù

et al. 2015

A&A

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We present the Multifrequency Snapshot Sky Survey (MSSS), the first northern-sky Low Frequency Array (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). The broadband frequency coverage, together with the fast survey speed generated by LOFAR's multibeaming capabilities, make MSSS the first survey of the sort anticipated to be carried out with the forthcoming Square Kilometre Array (SKA). Two of the sixteen frequency bands included in the survey were chosen to exactly overlap the frequency coverage of large-area Very Large Array (VLA) and Giant Metrewave Radio Telescope (GMRT) surveys at 74 MHz and 151 MHz respectively. The survey performance is illustrated within the MSSS Verification Field (MVF), a region of 100 square degrees centered at (α, δ) J2000 = (15 h , 69 • ). The MSSS results from the MVF are compared with previous radio survey catalogs. We assess the flux and astrometric uncertainties in the catalog, as well as the completeness and reliability considering our source finding strategy. We determine the 90% completeness levels within the MVF to be 100 mJy at 135 MHz with 108 resolution, and 550 mJy at 50 MHz with 166 resolution. Images and catalogs for the full survey, expected to contain 150 000-200 000 sources, will be released to a public web server. We outline the plans for the ongoing production of the final survey products, and the ultimate public release of images and source catalogs.

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“…As a detailed description of the whole process is beyond the scope of this paper, here we will illustrate only the most important steps. Interested readers can refer to Heald et al (2010). After correlation, data are recorded on storage nodes in the current LOFAR offline processing cluster.…”

Section: The Pipelinementioning

confidence: 99%

M 87 at metre wavelengths: the LOFAR picture

Gasperin

Orrù

Murgia

et al. 2012

A&A

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Context. M 87 is a giant elliptical galaxy located in the centre of the Virgo cluster, which harbours a supermassive black hole of mass 6.4 × 10 9 M , whose activity is responsible for the extended (80 kpc) radio lobes that surround the galaxy. The energy generated by matter falling onto the central black hole is ejected and transferred to the intra-cluster medium via a relativistic jet and morphologically complex systems of buoyant bubbles, which rise towards the edges of the extended halo. Aims. To place constraints on past activity cycles of the active nucleus, images of M 87 were produced at low radio frequencies never explored before at these high spatial resolution and dynamic range. To disentangle different synchrotron models and place constraints on source magnetic field, age and energetics, we also performed a detailed spectral analysis of M 87 extended radio-halo. Methods. We present the first observations made with the new Low-Frequency Array (LOFAR) of M 87 at frequencies down to 20 MHz. Three observations were conducted, at 15−30 MHz, 30−77 MHz and 116−162 MHz. We used these observations together with archival data to produce a low-frequency spectral index map and to perform a spectral analysis in the wide frequency range 30 MHz-10 GHz. Results. We do not find any sign of new extended emissions; on the contrary the source appears well confined by the high pressure of the intracluster medium. A continuous injection of relativistic electrons is the model that best fits our data, and provides a scenario in which the lobes are still supplied by fresh relativistic particles from the active galactic nuclei. We suggest that the discrepancy between the low-frequency radiospectral slope in the core and in the halo implies a strong adiabatic expansion of the plasma as soon as it leaves the core area. The extended halo has an equipartition magnetic field strength of 10 μG, which increases to 13 μG in the zones where the particle flows are more active. The continuous injection model for synchrotron ageing provides an age for the halo of 40 Myr, which in turn provides a jet kinetic power of 6−10 × 10 44 erg s −1 .

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Recent LOFAR imaging pipeline results

Cited by 24 publications

References 11 publications

Radiative age mapping of the remnant radio galaxy B2 0924+30: the LOFAR perspective

Radiative age mapping of the remnant radio galaxy B2 0924+30: the LOFAR perspective

The LOFAR Multifrequency Snapshot Sky Survey (MSSS)

M 87 at metre wavelengths: the LOFAR picture

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