Issue |
A&A
Volume 672, April 2023
|
|
---|---|---|
Article Number | A67 | |
Number of page(s) | 11 | |
Section | Astronomical instrumentation | |
DOI | https://doi.org/10.1051/0004-6361/202244573 | |
Published online | 31 March 2023 |
Robust analysis of differential Faraday rotation based on interferometric closure observables
1
Dpt. Astronomia i Astrofísica, Universitat de València,
C/ Dr. Moliner 50,
46120
Burjassot,
Spain
e-mail: ealruiz4@uv.es
2
Observatori Astronòmic, Universitat de València,
C/ Cat. José Beltrán 2,
46980
Paterna,
Spain
Received:
22
July
2022
Accepted:
5
March
2023
Polarization calibration of interferometric observations is a costly procedure and in some cases (e.g., due to limited coverage of paral-lactic angle for the calibrator), it may not be possible to carry out this process. To avoid this worst-case scenario, while extending the possibilities for the exploitation of polarization interferometric observations, the use of a new set of calibration-independent quantities (closure traces) has been proposed. However, these quantities suffer from some degeneracies, so their use in practical situations may be rather limited. In this paper, we explore the use of closure traces on simulated and real observations, showing that (with the proper selection of fitting parameters) it is possible to retrieve information on the source polarization using only closure traces and to constrain spatially resolved polarization. We carried out the first application of closure traces to the brightness modeling of real data, using the ALMA observations of M87 conducted during the April 2017 EHT campaign and quantifying a gradient in the Faraday rotation along the source structure (the M87 jet). This work opens the possibility to apply similar strategies to observations from any kind of interferometer (with a special focus on VLBI), whereby quantities such as the differential rotation measure or the spatially resolved polarization can be retrieved.
Key words: techniques: interferometric / polarization / radio continuum: general / techniques: polarimetric / methods: data analysis
© The Authors 2023
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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