Polarization Observations of a Split-band Type II Radio Burst from the Solar Corona

Abstract

Using temporal observations of circular polarized harmonic plasma emission from a split-band type II solar radio burst at 80 MHz, we separately estimated the coronal magnetic field strengths (B) associated with the lower (L) and upper (U) frequency bands of the burst. The corresponding Stokes I and V data were obtained with the polarimeter operating at the above frequency in the Gauribidanur observatory. The burst was associated with a flare/coronal mass ejection on the solar disk. Simultaneous spectral observations with the spectrograph there in the frequency range 80–35 MHz helped to establish that the observed polarized emission was from the harmonic component of the burst. The B values corresponding to the polarized emission from the L and U bands at 80 MHz are B L ≈ 1.2 G and B U ≈ 2.4 G, respectively. The different values of B for the observed harmonic emission at the same frequency (80 MHz) from the two bands imply unambiguously that the corresponding fundamental emission at 40 MHz must have originated at different spatial locations. Two-dimensional radio imaging observations of the burst with the radioheliograph in the same observatory at 80 MHz indicate the same. As comparatively higher B is expected behind a propagating shock due to compression as well as the corresponding coronal regions being closer to the Sun, our results indicate that the sources of L- and U-band emission should be located ahead of and behind the associated coronal shock, respectively. These are useful to understand the pre- and postshock corona as well as locations of electron acceleration in a propagating shock.

Solar Coronal Density Turbulence and Magnetic Field Strength at the Source Regions of Two Successive Metric Type II Radio Bursts

“…In the case of harmonic plasma emission, the associated B can be estimated in a relatively simple manner (see, e.g., Melrose et al 1980;Zlotnik 1981). Several such estimates of B using observations of weak circularly polarized emission from harmonic type II bursts are there in the literature (Hariharan et al 2014;Kumari et al 2017aKumari et al , 2019Ramesh et al 2022b;Ramesh & Kathiravan 2022c). The abovementioned work by various authors indicate that power spectral density (PSD) and/ or B are useful parameters to compare successive type II bursts.…”

Solar Radio Spectro-polarimeter (50–500 MHz). I. Design, Development, and Characterization of a Cross-polarized, Log-periodic Dipole Antenna

“…Furthermore, the changes in B near the source region of the above transients are essential ingredients to understand the strength and nature of the associated energy release (Ramesh et al 2020) and the polarization state as well. While the radio emission mechanism may be different (McLean 1985;Carley et al 2020) in different frequency ranges, the measured circular polarization always contains some information about B of the source region (refer Ramesh et al 2010;Hariharan et al 2015;Kumari et al 2019;Alissandrakis & Gary 2021;Ramesh & Kathiravan 2022, and the references therein). One may generally ignore linear polarization of the radio emission, particularly at low frequencies, since Faraday rotation of the plane of linear polarization is so large and frequency dependent that it is washed out when the radio emission is summed over any normal observing bandwidth (Hatanaka 1956;Grognard & McLean 1973).…”