A broadband microwave burst produced by electron beams

A. T. Altyntsev, Gregory Fleishman, G. L. Huang, V. F. Melnikov

Research output: Contribution to journalArticlepeer-review

39 Scopus citations


The theoretical and experimental study of fast electron beams attracts much attention in astrophysics and the laboratory. In the case of solar flares, the problem of reliable beam detection and diagnostics is of exceptional importance. This paper explores the fact that electron beams moving obliquely to the magnetic field or along the field with some angular scatter around the beam's propagation direction can generate microwave continuum bursts through the gyrosynchrotron mechanism. The characteristics of the microwave bursts produced by beams differ from those in the case of isotropic or loss-cone distributions, which suggests a new quantitative diagnostic for beams in the solar corona. To demonstrate the potential of this tool, we analyze a radio burst that occurred during an impulsive class 1B/M6.7 flare on 2001 March 10 (NOAA AR 9368; N27°, W42°). Based on detailed analysis of the spectral, temporal, and spatial relationships, we obtain firm evidence that the microwave continuum burst was produced by electron beams. We develop and apply a new forward-fitting algorithm based on the exact gyrosynchrotron formulae and employing both total-power and polarization measurements to solve the inverse problem of the beam diagnostics. The burst is found to have been generated by an oblique beam in a region of reasonably strong magnetic field (∼200-300 G) and observed at a quasi-transverse viewing angle. We find that the lifetime of the emitting electrons in the radio source was relatively short, τl ≈0.5 s, consistent with a single reflection of the electrons from a magnetic mirror at the footpoint with the stronger magnetic field. We discuss the implications of these findings for electron acceleration in flares and beam diagnostics.

Original languageEnglish (US)
Pages (from-to)1367-1377
Number of pages11
JournalAstrophysical Journal
Issue number2
StatePublished - Apr 20 2008

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Acceleration of particles
  • Sun: X-rays, gamma rays
  • Sun: flares
  • Sun: radio radiation


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