Speaker
Description
Absolute flux density calibration of the Sun is a challenging problem. Due to the very large field of view and high primary beam sidelobes of MWA, the measured flux density of a typical calibrator is significantly contaminated by solar contribution while the Sun is above the horizon. Hence calibrators are observed before sunrise and after sunset, resulting in a significant time separation between the calibrator and source observations. Additionally the Sun is observed using additional attenuation in the signal path, while the calibrators are not.
Absolute flux density calibration is however essential for several solar science goals. Oberoi et al. (2017) developed an innovative non-imaging technique for this. It yields ~10-60% uncertainty in flux density scale and depends on availability of multiple short baseline. The latter restricts its applicability for MWA phase-II extended configuration.
Our autonomous imaging pipeline for solar observations (AIRCARS; Mondal et al. 2019) gives us the ability to make very high dynamic range ($10^3-10^5$) solar images routinely. Recent improvements to this pipeline now allow us to detect several background galactic and extra-galactic sources in the presence of the Sun. We can now also image the large angular scale Galactic plane, with the Sun in the FoV. Taking advantage of this and the availability of catalogue flux densities of these in-field sources, we arrive at the absolute flux density calibration for the Sun. This method has lead to an order of magnitude reduction in the uncertainty on flux density calibration.
These developments also mark the next steps towards our long term science goals of extending the MWA IPS observation time window during the daytime and measuring the CME magnetic field using Faraday rotation of background linear polarized radiation.
