Energetic electron distribution in the solar flare

Details Energetic electron distribution in the solar flare Energetic electron distribution in the solar flare

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsh51e..03m&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #SH51E-03

Astronomy and Astrophysics

Astrophysics

[7514] Solar Physics, Astrophysics, And Astronomy / Energetic Particles, [7519] Solar Physics, Astrophysics, And Astronomy / Flares, [7534] Solar Physics, Astrophysics, And Astronomy / Radio Emissions, [7554] Solar Physics, Astrophysics, And Astronomy / X-Rays, Gamma Rays, And Neutrinos

Scientific paper

We investigate the distribution of energetic electrons in the solar flare by means of numerical simulations. First, we study the height distribution under an idealized model of time-varying, potential electromagnetic fields, by solving the drift-kinetic Vlasov equation (Minoshima et al. 2010, ApJ, 714, 332; 2011, ApJ, 732, 111). When pitch-angle scattering is not included, the peak heights of loop-top electrons are constant, regardless of their energy, owing to the continuous acceleration and compression of the electrons via shrinkage of magnetic loops. On the other hand, under pitch-angle scattering, the electron heights are energy-dependent: intermediate-energy electrons are at a higher altitude, whereas lower and higher energy electrons are at lower altitudes. This implies that the intermediate-energy electrons are inhibited from following the shrinking field lines to lower altitudes because pitch-angle scattering causes efficient precipitation of these electrons into the footpoint and their subsequent loss from the loop. This result can explain the energy-dependent height distribution of electrons, as indicated by coronal hard X-ray (HXR) and microwave sources (including the above-the-loop-top HXR source). Next, we perform the test particle simulation under the electromagnetic fields obtained from an MHD simulation of magnetic reconnection with different magnetic Reynolds numbers. When the Reynolds number is low, the reconnected fields are close to the potential one so that the result is very similar to the previous result. On the other hand, with the high Reynolds number, the fields significantly deviate from the potential. A rapid change of the magnetic field topology can violate the second adiabatic invariant of electrons. As a result, an impulsive electron flux appears along the field line, different from the low Reynolds number case. This may contribute to the electron precipitation into the footpoint, as indicated by a rapid temporal change of HXR emissions.

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