Thermal and Nonthermal Emissions of a Composite Flare Derived from NoRH and SDO Observations

Jeongwoo Lee, Stephen M. White, Ju Jing, Chang Liu, Satoshi Masuda, Jongchul Chae

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Differential emission measure (DEM) derived from the extreme ultraviolet (EUV) lines of the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory is used in the analysis of a solar flare observed by the Nobeyama Radioheliograph (NoRH). The target was a composite event consisting of an impulsive flare, SOL2015-06-21T01:42 (GOES class M2.0), and a gradual flare, SOL2015-06-21T02:36 (M2.6), for which separation of thermal plasma heating from nonthermal particle acceleration was of major interest. We have calculated the thermal free-free intensity maps with the AIA-derived DEM and compared them against the observed NoRH maps to attribute the difference to the nonthermal component. In this way, we were able to locate three distinct sources: the major source with thermal and nonthermal components mixed, a nonthermal source devoid of thermal particles, and a thermal source lacking microwave emission. Both the first and the second nonthermal sources produced impulsively rising 17 GHz intensities and moved away from the local magnetic polarization inversion lines in correlation with the flare radiation. In contrast, the thermal sources stay in fixed locations and show temporal variations of the temperature and emission measure uncorrelated with the flare radiation. We interpret these distinct properties as indicating that nonthermal sources are powered by magnetic reconnection and thermal sources passively receive energy from the nonthermal donor. The finding of these distinct properties between thermal and nonthermal sources demonstrates the microwave and EUV emission measure combined diagnostics.

Original languageEnglish (US)
Article number124
JournalAstrophysical Journal
Issue number2
StatePublished - Dec 1 2017

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Sun: activity
  • Sun: corona
  • Sun: flares
  • Sun: radio radiation
  • methods: data analysis


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