Robust direction-dependent gain-calibration of beam-modelling errors far from the target field
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| Názov: | Robust direction-dependent gain-calibration of beam-modelling errors far from the target field |
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| Autori: | S A Brackenhoff, A R Offringa, M Mevius, L V E Koopmans, J K Chege, E Ceccotti, C Höfer, L Gao, S Ghosh, F G Mertens, S Munshi |
| Prispievatelia: | POTHIER, Nathalie |
| Zdroj: | Monthly Notices of the Royal Astronomical Society. 541:3993-4010 |
| Publication Status: | Preprint |
| Informácie o vydavateľovi: | Oxford University Press (OUP), 2025. |
| Rok vydania: | 2025 |
| Predmety: | Cosmology and Nongalactic Astrophysics (astro-ph.CO), [PHYS.PHYS.PHYS-INS-DET] Physics [physics]/Physics [physics]/Instrumentation and Detectors [physics.ins-det], techniques: interferometric, first stars, reionization, software: simulations, Instrumentation and Methods for Astrophysics, FOS: Physical sciences, dark ages, [PHYS.ASTR] Physics [physics]/Astrophysics [astro-ph], Cosmology and Nongalactic Astrophysics, methods: data analysis, Instrumentation and Methods for Astrophysics (astro-ph.IM) |
| Popis: | Many astronomical questions require deep, wide-field observations at low radio frequencies. Phased arrays like LOFAR and SKA-Low (low band part of the Square Kilometre Array) 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 utilize 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 regularization 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 (High-Band Antennas of the Low Frequency Array) 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. |
| Druh dokumentu: | Article |
| Popis súboru: | application/pdf |
| Jazyk: | English |
| ISSN: | 1365-2966 0035-8711 |
| DOI: | 10.1093/mnras/staf1206 |
| DOI: | 10.48550/arxiv.2504.02483 |
| Prístupová URL adresa: | http://arxiv.org/abs/2504.02483 |
| Rights: | CC BY arXiv Non-Exclusive Distribution |
| Prístupové číslo: | edsair.doi.dedup.....899fa0e65a8eb1d2e90e8f1963844197 |
| Databáza: | OpenAIRE |
Nájsť tento článok vo Web of Science | Abstrakt: | Many astronomical questions require deep, wide-field observations at low radio frequencies. Phased arrays like LOFAR and SKA-Low (low band part of the Square Kilometre Array) 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 utilize 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 regularization 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 (High-Band Antennas of the Low Frequency Array) 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. |
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| ISSN: | 13652966 00358711 |
| DOI: | 10.1093/mnras/staf1206 |