Robust direction-dependent gain-calibration of beam-modelling errors far from the target field

Abstract

Many astronomical questions require deep, wide-field observations at low radio frequencies. Phased arrays like LOFAR and SKA-low are designed for this, but have inherently unstable element gains, leading to time, frequency and direction-dependent gain errors. Precise direction-dependent calibration of observations is therefore key to reaching the highest possible dynamic range. Many tools for direction-dependent calibration utilise sky and beam models to infer gains. However, these calibration tools struggle with precision calibration for relatively bright (e.g. A-team) sources far from the beam centre. Therefore, the point-spread-function of these sources can potentially obscure a faint signal of interest. We show that, and why, the assumption of a smooth gain solution per station fails for realistic radio interferometers, and how this affects gain-calibration results. Subsequently, we introduce an improvement for smooth spectral gain constraints for direction-dependent gain-calibration algorithms, in which the level of regularisation is weighted by the expected station response to the sky model. We test this method using direction-dependent calibration method DDECal and physically-motivated beam modelling errors for LOFAR-HBA stations. The new method outperforms the standard method for various calibration settings near nulls in the beam, and matches the standard inverse-variance-weighted method's performance for the remainder of the data. The proposed method is especially effective for short baselines, both in visibility and image space. Improved direction-dependent gain-calibration is critical for future high-precision SKA-low observations, where higher sensitivity, increased antenna beam complexity, and mutual coupling call for better off-axis source subtraction, which may not be achieved through improved beam models alone.

16 pages, 10 figures

References in corpus (52)

• Array Programming with NumPy
• Astropy: A Community Python Package for Astronomy
• The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package
• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• LOFAR: The LOw-Frequency ARray
• CASA, the Common Astronomy Software Applications for Radio Astronomy
• WSClean: an implementation of a fast, generic wide-field imager for radio astronomy
• The GMRT 150 MHz All-sky Radio Survey: First Alternative Data Release TGSS ADR1
• The LOFAR Two-metre Sky Survey - I. Survey Description and Preliminary Data Release
• GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey I: A low-frequency extragalactic catalogue
• The LOFAR Two-metre Sky Survey -- V. Second data release
• The VLA Low-frequency Sky Survey
• A morphological algorithm for improving radio-frequency interference detection
• Science with the Murchison Widefield Array
• Improved upper limits on the 21-cm signal power spectrum of neutral hydrogen at $\mathbf{z}\approx 9.1$ from LOFAR
• Upper limits on the 21-cm Epoch of Reionization power spectrum from one night with LOFAR
• LOFAR facet calibration
• Revisiting the radio interferometer measurement equation. I. A full-sky Jones formalism
• Deep multi-redshift limits on Epoch of Reionisation 21cm Power Spectra from Four Seasons of Murchison Widefield Array Observations
• Systematic effects in LOFAR data: A unified calibration strategy
• Radio interferometric gain calibration as a complex optimization problem
• The Cosmic Dawn and Epoch of Reionization with the Square Kilometre Array
• Revisiting the radio interferometer measurement equation. II. Calibration and direction-dependent effects
• VAST: An ASKAP Survey for Variables and Slow Transients
• The Impact of Modeling Errors on Interferometer Calibration for 21 cm Power Spectra
• Systematic biases in low frequency radio interferometric data due to calibration: the LOFAR EoR case
• Distributed Radio Interferometric Calibration
• The LOFAR Two-metre Sky Survey Deep Fields Data Release 1: V. Survey description, source classifications and host galaxy properties
• Spectral calibration requirements of radio interferometers for Epoch of Reionisation science with the SKA
• First upper limits on the 21 cm signal power spectrum from cosmic dawn from one night of observations with NenuFAR
• The 154 MHz radio sky observed by the Murchison Widefield Array: noise, confusion and first source count analyses
• Unified Radio Interferometric Calibration and Imaging with Joint Uncertainty Quantification
• The LOFAR LBA Sky Survey II. First data release
• Quantifying Suppression of the Cosmological 21-cm Signal due to Direction Dependent Gain Calibration in Radio Interferometers
• In situ measurement of MWA primary beam variation using ORBCOMM
• LOFAR observations of the XMM-LSS field
• Non-convex optimization for self-calibration of direction-dependent effects in radio interferometric imaging
• Precision requirements for interferometric gridding in 21-cm power spectrum analysis
• Ionospheric Power-Spectrum Tomography in Radio Interferometry
• Deeper multi-redshift upper limits on the Epoch of Reionization 21-cm signal power spectrum from LOFAR between z=8.3 and z=10.1
• Bayesian radio interferometric imaging with direction-dependent calibration
• Assessing the impact of two independent direction-dependent calibration algorithms on the LOFAR 21-cm signal power spectrum
• Measuring HERA's primary beam in-situ: methodology and first results
• Statistical analysis of the causes of excess variance in the 21 cm signal power spectra obtained with the Low-Frequency Array
• Primary beam effects of radio astronomy antennas: I. Modelling the Karl G. Jansky Very Large Array (VLA) L-band beam using holography
• Polca SARA - Full polarization, direction-dependent calibration and sparse imaging for radio interferometry
• On the use of temporal filtering for mitigating galactic synchrotron calibration bias in 21 cm reionization observations
• Beyond the horizon: Quantifying the full sky foreground wedge in the cylindrical power spectrum
• Probabilistic direction-dependent ionospheric calibration for LOFAR-HBA
• Ionospheric contributions to the excess power in high-redshift 21-cm power-spectrum observations with LOFAR
• Spectral modelling of Cygnus A between 110 and 250 MHz. Impact on the LOFAR 21-cm signal power spectrum
• Investigating mutual coupling in the MWA Phase II compact array

Cited by in corpus (3)

• Improved upper limits on the 21-cm signal power spectrum at $z=17.0$ and $z=20.3$ from an optimal field observed with NenuFAR
• The impact of lunar topography on the 21-cm power spectrum for grid-based arrays : Insights for the Dark-ages EXplorer (DEX)
• Mitigating incoherent excess variance in high-redshift 21 cm observations with multi-output cross-Gaussian process regression