Estimates of Magnetic Field Strength in the Solar Corona Using Observations of Thermal Radio Emission at Low Frequencies
- 1Indian Institute of Astrophysics
Abstract
Measurements of the magnetic field strength in the solar corona at heliocentric distances r ≳ 1.1 R ⊙ , using observations other than transient radio bursts, are rare. Circular polarization observations of thermal bremsstrahlung radio emission at frequencies <100 MHz, which typically originate at r > 1.1 R ⊙ in the solar corona, can be effectively used for this purpose. The thermal bremsstrahlung emission is randomly polarized, but in the presence of a magnetic field, it propagates in two oppositely polarized circular modes whose differential absorption in the medium results in an observable circular polarization. We report a case study of two-dimensional imaging observations of the abovementioned circular polarization in the solar corona at 51 MHz using the Gauribidanur Radioheliograph (GRAPH) and estimates of the associated coronal magnetic field strength. The peak degree of circular polarization ( dcp ), calculated from the observed total and circularly polarized intensity images with the GRAPH, is ≈2.7%. Using ray-tracing simulations, we find that the observed peak dcp corresponds to a radio source located at r ≈ 1.65 ± 0.15 R ⊙ at 51 MHz, and its field strength is ≈ 1.55 ± 0.3 Gauss.
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BibTeX
@article{shaik2026estimates,
title = {{Estimates of Magnetic Field Strength in the Solar Corona Using Observations of Thermal Radio Emission at Low Frequencies}},
author = {Sayuf Shaik and C. Kathiravan and R. Ramesh},
journal = {The Astrophysical Journal},
year = {2026},
month = nov,
doi = {10.3847/1538-4357/aeaa33},
url = {https://iopscience.iop.org/article/10.3847/1538-4357/aeaa33},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Estimates of Magnetic Field Strength in the Solar Corona Using Observations of Thermal Radio Emission at Low Frequencies
AU - Sayuf Shaik
AU - C. Kathiravan
AU - R. Ramesh
PY - 2026
DA - 2026/11/05
JO - The Astrophysical Journal
DO - 10.3847/1538-4357/aeaa33
UR - https://iopscience.iop.org/article/10.3847/1538-4357/aeaa33
AB - Measurements of the magnetic field strength in the solar corona at heliocentric distances r ≳ 1.1 R ⊙ , using observations other than transient radio bursts, are rare. Circular polarization observations of thermal bremsstrahlung radio emission at frequencies <100 MHz, which typically originate at r > 1.1 R ⊙ in the solar corona, can be effectively used for this purpose. The thermal bremsstrahlung emission is randomly polarized, but in the presence of a magnetic field, it propagates in two oppositely polarized circular modes whose differential absorption in the medium results in an observable circular polarization. We report a case study of two-dimensional imaging observations of the abovementioned circular polarization in the solar corona at 51 MHz using the Gauribidanur Radioheliograph (GRAPH) and estimates of the associated coronal magnetic field strength. The peak degree of circular polarization ( dcp ), calculated from the observed total and circularly polarized intensity images with the GRAPH, is ≈2.7%. Using ray-tracing simulations, we find that the observed peak dcp corresponds to a radio source located at r ≈ 1.65 ± 0.15 R ⊙ at 51 MHz, and its field strength is ≈ 1.55 ± 0.3 Gauss.
SN - 1538-4357
SN - 0004-637X
ER -