Gyrosynchrotron Emission Generated by Nonthermal Electrons with the Energy Spectra of a Broken Power Law

Zhao Wu, Yao Chen, Hao Ning, Xiangliang Kong, Jeongwoo Lee

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8 Scopus citations


The latest observational reports of solar flares reveal some uncommon features of microwave spectra, such as unusually hard (or even positive) spectra and/or a super-high peak frequency. For a better understanding of these features, we conduct a parameter study to investigate the effect of broken-power-law spectra of energetic electrons on microwave emission on the basis of the gyrosynchrotron mechanism. The electron broken-power-law energy distribution is characterized by three parameters - the break energy (E B ) and the power-law indices below (δ 1 ) and above (δ 2 ) the break energy. We find that with the addition of the δ 2 component of the electron spectra, the total flux density can increase by several times in the optically thick regime, and by orders of magnitude in the optically thin regime; the peak frequency (ν p ) also increases and can reach up to tens of gigahertz; and the degree of polarization (r c ) decreases in general. We also find that (1) the variation of the flux density is much larger in the optically thin regime, and the microwave spectra around the peak frequency manifest various profiles with a softening or soft-hard pattern; (2) the parameters δ 1 and E B affect the microwave spectral index (α) and the degree of polarization (r c ) mainly in the optically thick regime, while δ 2 mainly affects the optically thin regime. The results are helpful in understanding the recently reported microwave bursts with unusual spectral features and indicate the demands for a more complete spectral coverage of microwave bursts, especially in the high-frequency regime, say >10-20 GHz.

Original languageEnglish (US)
Article number22
JournalAstrophysical Journal
Issue number1
StatePublished - Jan 20 2019
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Sun: X-rays, gamma rays
  • Sun: corona
  • Sun: radio radiation


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