A Novel Calibration and Imaging Method for ALMA Observations of SgrA*
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arXiv
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| Format: | Preprint |
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2025
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| _version_ | 1866916724425621504 |
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| author | Albentosa-Ruiz, Ezequiel Martí-Vidal, Iván Goddi, Ciriaco Mus, Alejandro |
| author_facet | Albentosa-Ruiz, Ezequiel Martí-Vidal, Iván Goddi, Ciriaco Mus, Alejandro |
| contents | This document presents a novel method for the intra-field calibration and imaging of the radio source SgrA*, observed with the Atacama Large Millimeter/submillimeter Array (ALMA). SgrA* is a complex source comprising two components: the compact core (which exhibits high variability) and the extended minispiral (which is relatively stable over short timescales). The novel approach consists in a self-calibration method that employs the extended structure of the source (the minispiral) to calibrate the flux variability of the compact core. The algorithm involves several steps: (1) an initial CLEAN image is generated for the entire source; (2) the core is subtracted, leaving only the minispiral; (3) a two-component visibility model is constructed, comprising the minispiral and the core; (4) the model is fitted to the data, retrieving flux density parameters for each integration time; and (5) the data are scaled and calibrated, resulting in nearly constant brightness for the minispiral and variable flux for the core. The implementation of this algorithm through a script in the CASA package is described, detailing the configuration parameters and the steps involved. The success of the method is demonstrated through light curves of SgrA* observed on day 21 April 2018 in Band 6, as part of the 2018 EHT campaign. The light curves have been produced for Stokes I (total intensity), linear polarized intensity, EVPA (electric vector position angle), and Stokes V (circular polarization), providing valuable insights into the variability of this radio source. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2503_11258 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | A Novel Calibration and Imaging Method for ALMA Observations of SgrA* Albentosa-Ruiz, Ezequiel Martí-Vidal, Iván Goddi, Ciriaco Mus, Alejandro Instrumentation and Methods for Astrophysics This document presents a novel method for the intra-field calibration and imaging of the radio source SgrA*, observed with the Atacama Large Millimeter/submillimeter Array (ALMA). SgrA* is a complex source comprising two components: the compact core (which exhibits high variability) and the extended minispiral (which is relatively stable over short timescales). The novel approach consists in a self-calibration method that employs the extended structure of the source (the minispiral) to calibrate the flux variability of the compact core. The algorithm involves several steps: (1) an initial CLEAN image is generated for the entire source; (2) the core is subtracted, leaving only the minispiral; (3) a two-component visibility model is constructed, comprising the minispiral and the core; (4) the model is fitted to the data, retrieving flux density parameters for each integration time; and (5) the data are scaled and calibrated, resulting in nearly constant brightness for the minispiral and variable flux for the core. The implementation of this algorithm through a script in the CASA package is described, detailing the configuration parameters and the steps involved. The success of the method is demonstrated through light curves of SgrA* observed on day 21 April 2018 in Band 6, as part of the 2018 EHT campaign. The light curves have been produced for Stokes I (total intensity), linear polarized intensity, EVPA (electric vector position angle), and Stokes V (circular polarization), providing valuable insights into the variability of this radio source. |
| title | A Novel Calibration and Imaging Method for ALMA Observations of SgrA* |
| topic | Instrumentation and Methods for Astrophysics |
| url | https://arxiv.org/abs/2503.11258 |