Decoherence in LOFAR-VLBI Beamforming

Abstract

We show that the use of a superstation (a phased array created using multiple stations of an interferometric array) created in post-processing for LOFAR-VLBI observations introduces a direction-dependent loss of signal in the image. We show this effect using simulations and real data. Using the RIME formalism, we characterise it fully, and give limits under which this signal loss is negligible. Finally, we show that we are able to fully predict this effect. We close with guidelines for interferometric observers to avoid this effect in their observations, and a discussion of techniques which could limit this effect or do away with it entirely. The latter in particular will be relevant to the SKA should its long baselines be used to their fullest potential.

arXiv comment14 pages, 5 figures

References in corpus (15)

• LOFAR: The LOw-Frequency ARray
• The LOFAR Two-metre Sky Survey - II. First data release
• Revisiting the radio interferometer measurement equation. I. A full-sky Jones formalism
• Faceting for direction-dependent spectral deconvolution
• Radio interferometric gain calibration as a complex optimization problem
• Revisiting the radio interferometer measurement equation. II. Calibration and direction-dependent effects
• LBCS: the LOFAR Long-Baseline Calibrator Survey
• A wide-band, active antenna system for long wavelength radio astronomy
• Subarcsecond international LOFAR radio images of Arp 220 at 150 MHz: A kpc-scale star forming disk surrounding nuclei with shocked outflows
• Subarcsecond international LOFAR radio images of the M82 nucleus at 118 MHz and 154 MHz
• Revisiting the radio interferometer measurement equation. III. Addressing direction-dependent effects in 21 cm WSRT observations of 3C 147
• LOFAR VLBI Studies at 55 MHz of 4C 43.15, a z=2.4 Radio Galaxy
• Revisiting the radio interferometer measurement equation. IV. A generalized tensor formalism
• LOFAR Measures the Hotspot Advance Speed of the High-Redshift Blazar S5 0836+710
• Baseline-dependent sampling and windowing for radio interferometry: data compression, field-of-interest shaping and outer field suppression

Cited by in corpus (3)

• Sub-arcsecond imaging with the International LOFAR Telescope I. Foundational calibration strategy and pipeline
• A MeerKAT-meets-LOFAR Study of MS 1455.0+2232: A 590 kiloparsec 'Mini'-Halo in a Sloshing Cool-Core Cluster
• Fast algorithms to approximate the position-dependent point spread function responses in radio interferometric wide-field imaging