LOFAR FACET CALIBRATION

By R. Weeren, W. Williams, M. Hardcastle, T. Shimwell, D. Rafferty, J. Sabater, G. Heald, S. Sridhar, T. J. Dijkema, Gianfranco Brunetti and 32 more. 2016

157 citations recorded by the source corpus.

LOFAR, the Low-Frequency Array, is a powerful new radio telescope operating between 10 and 240 MHz. LOFAR allows detailed sensitive high-resolution studies of the low-frequency radio sky. At the same time LOFAR also provides excellent short baseline coverage to map diffuse extended emission. However, producing high-quality deep images is challenging due to the presence of direction-dependent calibration errors, caused by imperfect knowledge of the station beam shapes and the ionosphere. Furthermore, the large data volume and presence of station clock errors present additional difficulties. In this paper we present a new calibration scheme, which we name facet calibration, to obtain deep high-resolution LOFAR High Band Antenna images using the Dutch part of the array. This scheme solves and corrects the direction-dependent errors in a number of facets that cover the observed field of view. Facet calibration provides close to thermal noise limited images for a typical 8 hr observing run at ∼ 5 ″ resolution, meeting the specifications of the LOFAR Tier-1 northern survey.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/d20457931dd42300fef9941c58a98dd127da1595

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

1. G. Mellema
2. Ilian Iliev
3. Benedetta Ciardi
4. M. Hardcastle
5. P. Best
6. Joop Schaye
7. D. Frail
8. Florent Mertens

In Nuclear and High Energy Physics

1. M. Haverkorn
2. D. Frail
3. Florent Mertens
4. Joop Schaye
5. Matthias Hoeft
6. R. Weeren
7. G. Mellema
8. J. Oonk

Citations in the corpus

• The GMRT 150 MHz all-sky radio survey - First alternative data release TGSS ADR1 (2016, background): “…wide-field observations into high-quality images, as is witnessed by a rich number of publications on the topic over the last decade (e.g., Noordam 2004; Cotton 2005; Mitchell et al. 2008; Intema et al. 2009; Wijnholds et al. 2010; Smirnov 2011; Arora et al. 2015; van Weeren et al. 2016).”
• The LOFAR Two-metre Sky Survey. I. Survey description and preliminary data release (2016, methodology): “Several approaches are being developed to minimise these direction-dependent effects (e.g. Tasse 2014 and Yatawatta 2015), including the facet calibration procedure (van Weeren et al. 2016a and Williams et al. 2016).”
• An optimized algorithm for multiscale wideband deconvolution of radio astronomical images (2017, methodology): “This is the method currently employed in the Factor pipeline (Van Weeren et al. 2016) for direction-dependent calibration of LOFAR data.”
• Improved upper limits on the 21 cm signal power spectrum of neutral hydrogen at z ≈ 9.1 from LOFAR (2020, methodology): “In the future, we plan to investigate the reduction of this solution time interval and to decouple the phase and amplitude solution time (e.g van Weeren et al. 2016).”