Manifestations of energetic electrons with anisotropic distributions in solar flares. II. Gyrosynchrotron microwave emission

Kuznetsov, Alexey A. and Zharkova, Valentina (2010) Manifestations of energetic electrons with anisotropic distributions in solar flares. II. Gyrosynchrotron microwave emission. The Astrophysical Journal, 722. pp. 1577-1588. ISSN 0004-637X

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Abstract

We investigate the spectra and polarization of the gyrosynchrotron microwave (MW) emission generated by
anisotropic electron beams in the solar corona. The electron distributions are selected from the steady propagation/ precipitation model of beam electrons obtained from the time-dependent solutions of the FokkerPlanck equation taking into account particle anisotropic precipitation into a converging magnetic tube while losing energy in collisions and Ohmic losses induced by a self-induced electric field.We separate the effects of converging magnetic field from those of self-induced electric field for beams with different initial energy fluxes and spectral indices. The effect of returning electrons of the beam is negligible for the beams with relatively weak energy fluxes (F 1010 erg cm2 s1), while it becomes very important for the electron beams with F 1012 erg cm2 s1. Electric field-induced losses lead to the increase of MW emission intensity, especially at larger viewing angles ( 140, looking at the loop from a side). The polarization remains typical for the beam-like distributions. The combined effect of the self-induced electric field and converging magnetic field reveals a noticeable (up to a factor of 10) increase of the emission intensity (for the viewing angles 140150) in comparison with the models considering only collision factor, especially in the deeper precipitation layers (near the loop footpoints). Thus, considering the self-induced electric field is especially important for the resulting MW emission intensity, spectra shape, and polarization that can provide much closer correlation of simulations with observations in solar flares.

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