# Direct Estimates of the Solar Coronal Magnetic Field Using Contemporaneous Extreme-ultraviolet, Radio, and White-light Observations

## TL;DR

This study combines EUV, radio, and white-light observations to directly estimate the magnetic field in the solar corona, revealing a consistent magnetic field profile without relying on prior density models.

## Contribution

It presents a novel method for direct coronal magnetic field estimation using simultaneous multi-wavelength data, including EUV flux ropes and type II radio bursts.

## Key findings

- Magnetic field varies as B(r) = 2.61 × r^{-2.21} G from 1.1 to 2.2 solar radii.
- Empirical electron density model constructed from combined observations.
- First direct estimates of coronal magnetic field using co-temporal radio and white-light data.

## Abstract

We report a solar coronal split-band type II radio burst that was observed on 2016 March 16 with the Gauribidanur Radio Spectro-Polarimeter (GRASP) in the frequency range $\approx$\,90\,-\,50 MHz, and the Gauribidanur RadioheliograPH (GRAPH) at two discrete frequencies, viz. 80 MHz and 53.3 MHz. Observations around the same epoch in extreme-ultraviolet (EUV) and white-light show that the above burst was associated with a flux rope structure and a coronal mass ejection (CME), respectively. The combined height-time plot generated using EUV, radio, and whitelight data suggest that the different observed features (i.e. the flux rope, type II burst and the CME) are all closely associated. We constructed an empirical model for the coronal electron density distribution ($N_{e}(r)$, where $r$ is the heliocentric distance) from the above set of observations themselves and used it to estimate the coronal magnetic field strength ($B$) over the range of $r$ values in which the respective events were observed. The $B$ values are consistent with each other. They vary as $B(r)\,=\,2.61 \times r^{-2.21}$ \textrm{G} in the range $r \approx$\,1.1\,-\,2.2$\rm R_{\odot}$. As far as we know, similar `direct' estimates of $B$ in the near-Sun corona without assuming a model for $N_{e}(r)$, and by combining co-temporal set of observations in two different regions (radio and whitelight) of the electromagnetic spectrum, have rarely been reported. Further, the present work is a novel attempt where the characteristics of a propagating EUV flux rope structure, considered to be the signature of a CME close the Sun, have been used to estimate $B(r)$ in the corresponding distance range.