| Name: | Soham Dey |
| Affiliation: | National Centre for Radio Astronomy |
| Conference ID : | ASI2024_150 |
| Title : | First robust detection of linear polarization from solar radio bursts |
| Authors : | Soham Dey1, Devojyoti Kansabanik1, Surajit Mondal2, Divya Oberoi1 |
| Authors Affiliation: | 1. National Centre for Radio Astrophysics, Pune-411007, India
2. New Jersey Institute of Technology, Newark, NJ 07102, United States |
| Mode of Presentation: | Poster |
| Abstract Category : | Sun, Solar System, Exoplanets, and Astrobiology |
| Abstract : | Polarization observations of solar radio emissions have been primarily focused on circular polarization, because no linear polarization is expected from solar radio emission (e.g., Grognard & McLean 1973). This is due to high differential Faraday rotation which washes out any traces of linear polarization as the emission propagates through the coronal plasma. Previous polarimetric studies of solar radio bursts were mostly based on dynamic spectra; any detection of linear polarization was assumed to be of instrumental origin (e.g Grognard & McLean 1972; Boischot & Lecacheux 1975). This assumption has been routinely used in calibrating solar polarimetric observations, even for recent studies (Morosan et al. 2022). State-of-the-art polarimetric calibration algorithm, P-AIRCARS (Kansabanik et al., 2022, 2023) does not rely on such assumptions and provides high-fidelity and high-dynamic-range spectro-polarimetric snapshot images using new generation instruments like the Murchison Widefield Array (MWA). This enables us to explore a part of phase space which was hitherto inaccessible. We have found the first robust imaging based evidences of linearly polarized emission from solar radio bursts at metre wavelengths. This has also been confirmed by simultaneous observation with the MWA and the upgraded Giant Metrewave Radio Telescope at the same spectral band. We estimated the upper limit on the Rotation Measure (RM) to be ~ 50 rad m-2, which is much lower than that estimated earlier (e.g., 10^3 rad m-2 estimated by Bhonsle & McNarry 1964). The low value of the RM implies that the linear polarization must originate at much larger coronal heights, and hence passes through a much lesser coronal plasma. Interestingly, a few instances of detection of linear polarization from stellar radio bursts have recently been reported as well (Callingham et al., 2021, Bastian et al. 2022). We also present our initial explorations of physical scenarios which can give rise to such linearly polarized emission. |
