| Name: | Deepan Patra |
| Affiliation: | National Centre for Radio Astrophysics |
| Conference ID : | ASI2024_252 |
| Title : | A Low Frequency Polarimetric Study of Coronal Holes |
| Authors : | Deepan Patra1, Devojyoti Kansabanik1, Soham Dey1, Divya Oberoi1 |
| Authors Affiliation: | 1. National Centre for Radio Astrophysics, Pune-411007,India |
| Mode of Presentation: | Poster |
| Abstract Category : | Sun, Solar System, Exoplanets, and Astrobiology |
| Abstract : | Coronal holes are low density and cooler regions compared to the surrounding solar corona and show up as brightness depression in extreme ultraviolet (EUV) and X-ray images. They are open magnetic field regions along which charged particles and plasma flow out easily. In the radio wavelength, the imaging studies of coronal holes have been comparatively limited and mostly been done in total intensity (Stokes I). However, with the new instruments like Murchison Widefield Array (MWA), it has been possible to perform high-fidelity and high-dynamic-range spectropolarimetric imaging studies of the quiet sun. McCauley et. al. 2019 (hereafter M19) presented the first spectro-polarimetric study of the quiet sun using the MWA. They studied the circular polarisation (Stokes V) images of low-latitude coronal holes in the frequency range 80-240 MHz. Their most interesting and also surprising finding was the characteristic `bullseye’ feature, where the central part of the coronal hole has a certain polarisation sense and is surrounded by a ring of the opposite polarisation. They also reported that the central polarisation of the coronal hole did not match the expectation from thermal Bremsstrahlung. Certain limitations in their analysis cast a shadow of doubt on the correctness of these results. These limitations have since been overcome by the recently developed state-of-the-art polarimetric solar radio imaging pipeline - P-AIRCARS (Kansabanik et. al., 2022, 2023). In this work we have reanalysed the same data using P-AIRCARS to verify the presence of the bullseye feature. Our analysis verifies the bullseye structure to be real, though its polarisation sense is opposite to that found by M19 and the polarisation fraction is also smaller than their estimate. The presence of such a large-scale circularly polarised structure poses an interesting question about its origin and is under investigation. |
