Radio Bursts and Magnetic Field Structure During Microflares
Abstract
This paper presents an analysis of two selected microflares seen in dynamic radio spectra recorded by the Astrophysical Institute Potsdam and imaged by the Nançay Multifrequency Radioheliograph. The microflares were observed in hard X-rays by the Ramaty High Energy Solar Spectroscopic Imager in AR 10465 on September 26, 2003. Magnetic field connections are selected compatible with the spatial extent of the HXR sources and the Transition Region and Coronal Explorer-detected chromospheric UV continuum brightenings. The selected field lines are a small subset of the potential extrapolation of a SOHO--Michelson Doppler Imager high resolution magnetogram. For a type III-associated microflare a loop-like magnetic field structure is found with a spatial extent of ≈35 arcsec. A type II-precursor-associated (stronger) microflare brightened in a smaller-scale circularly arranged arcade formed by field lines of about 12 arcsec foot point distance. All microflare site-compatible field lines have turning points in heights of 5--20 arcsec and are situated underneath larger-scale arcades joining the main leading and trailing field concentrations. For understanding type III-burst source positions, an electron path must exist between the HXR source site and large-scale open field lines in the trailing part of AR 10465. This demands for reconnection of the selected small-scale closed field lines with overlying field systems, electron propagation to the trailing spot, and diffusion from closed to open field lines leading out into the solar wind. The type II burst precursor sources are formed in a magnetic hole of the potential field. This supports the view of a growing large amplitude flare wave which is not intense enough to raise to a spatially extended type II-exciting shock front but to smaller-scale sub-shocks forming the radio precursor burst sources.
- Publication:
-
Central European Astrophysical Bulletin
- Pub Date:
- 2009
- Bibcode:
- 2009CEAB...33..159A
- Keywords:
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- Sun;
- corona;
- flare;
- magnetic field;
- radio emission;
- X-rays