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

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${\mathrm{R}}_{\odot }$. 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.

arXiv comment11 pages, 8 figures, 3 tables; Accepted for publication in ApJ

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• Imaging-spectroscopy of a band-split type II solar radio burst with the Murchison Widefield Array
• Exploring the circular polarisation of low-frequency solar radio bursts with LOFAR
• Solar Coronal Magnetic Fields and Sensitivity Requirements for Spectropolarimetry Channel of VELC Onboard Aditya-L1
• Trends and Characteristics of High-Frequency Type II Bursts Detected by CALLISTO Spectrometers
• Imaging and Spectral Observations of a Type-II Radio Burst Revealing the Section of the CME-Driven Shock that Accelerates Electrons
• Solar coronal density turbulence and magnetic field strength at the source regions of two successive metric type II radio bursts
• Electron acceleration and radio emission following the early interaction of two coronal mass ejections
• 3D coupled tearing-thermal evolution in solar current sheets
• New results on the direct observations of thermal radio emission from a solar coronal mass ejection
• Spectral lines in FUV and EUV for diagnosing coronal magnetic field
• Global Coronal Magnetic Field Estimation Using Bayesian Inference
• Type IV Radio Bursts and Associated Active Regions in the Sunspot Cycle 24
• Imaging and spectropolarimetric observations of a band-split type II solar radio burst with LOFAR
• Solar radio bursts observations by Egypt- Alexandria CALLISTO spectrometer: First results