Spectral Analysis of Solar Radio Type III Bursts from 20 kHz to 410 MHz

Abstract

We present the statistical analysis of the spectral response of solar radio type III bursts over the wide frequency range between 20 kHz and 410 MHz. For this purpose, we have used observations that were carried out using both spaced-based (Wind/Waves) and ground-based (Nançay Decameter Array and Nançay Radioheliograph) facilities. In order to compare the flux densities observed by the different instruments, we have carefully calibrated the data and displayed them in Solar Flux Units. The main result of our study is that type III bursts, in the metric to hectometric wavelength range, statistically exhibit a clear maximum of their median radio flux density around 2 MHz. Although this result was already reported by inspecting the spectral profiles of type III bursts in the frequency range 20 kHz - 20 MHz, our study extends such analysis for the first time to metric radio frequencies (i.e., from 20 kHz to 410 MHz) and confirms the maximum spectral response around 2 MHz. In addition, using a simple empirical model we show that the median radio flux $S$ of the studied dataset obeys the polynomial form $Y=0.04X^3-1.63X^2+16.30X-41.24$, with $X=\ln (F_{\text{MHz}})$ and with $Y=\ln (S_{\text{SFU}})$. Using the Sittler and Guhathakurtha model for coronal streamers \citep{Sit1999}, we have found that maximum of radio power falls therefore in the range 4 to 10 $R_{\odot }$, depending on whether the type III emissions are assumed to be at the fundamental or the harmonic.

21 Pages, 6 Figures, 1 Table, Accepted for publication in the Astrophysical Journal

References in corpus (5)

• Dynamics of electron beams in the solar corona plasma with density fluctuations
• Low frequency observations of transient quasi-periodic radio emission from the solar atmosphere
• Statistical Survey of Type III Radio Bursts at Long Wavelengths Observed by the Solar TErrestrial RElations Observatory (STEREO)/Waves Instruments: Radio Flux Density Variations with Frequency
• Coronal type III radio bursts and their X-ray flare and interplanetary type III counterparts
• A Statistical Study of Low-frequency Solar Radio Type-III Bursts

Cited by in corpus (1)

• Solar Coronal Magnetic Fields and Sensitivity Requirements for Spectropolarimetry Channel of VELC Onboard Aditya-L1