Spatial and spectral behaviors of solar flares observed in microwaves

Document Type

Article

Publication Date

7-1-2009

Abstract

The spatial and spectral behaviors of two solar flares observed by the Nobeyama Radioheliograph (NoRH) on 24 August 2002 and 22 August 2005 are explored. They were observed with a single loop-top source and double footpoint sources at the beginning, then with looplike structures for the rest of the event. NoRH has high spatial and temporal resolution at the two frequencies of 17 and 34 GHz where a nonthermal radio source is often optically thin. Such capabilities give us an opportunity to study the spatial and spectral behaviors of different microwave sources. The 24 August 2002 flare displayed a soft-hard-soft (SHS) spectral pattern in the rising-peak-decay phases at 34 GHz, which was also observed for the spectral behavior of both loop-top and footpoint sources. In ontrast, the 22 August 2005 flare showed a soft-hard-harder (SHH) spectral pattern for its both loop-top and footpoint sources. It is interesting that this event showed a harder spectrum in the early rising phase. We found a positive correlation between the spectral index and microwave flux in both the loop-top source and the footpoint sources in both events. The conclusions drawn from the flux index could apply to the electron index as well, because of their simple linear relationship under the assumption of nonthermal gyrosynchrotron mechanism. Such a property of spatial and spectral behaviors of microwave sources gives an observational constraint on the electron acceleration mechanism and electron propagation. © 2009 Springer Science+Business Media B.V.

Identifier

67650690568 (Scopus)

Publication Title

Solar Physics

External Full Text Location

https://doi.org/10.1007/s11207-009-9388-8

e-ISSN

1573093X

ISSN

00380938

First Page

335

Last Page

350

Issue

2

Volume

257

Grant

0847126

Fund Ref

National Science Foundation

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