Issue |
A&A
Volume 457, Number 2, October II 2006
|
|
---|---|---|
Page(s) | 693 - 697 | |
Section | The Sun | |
DOI | https://doi.org/10.1051/0004-6361:20054438 | |
Published online | 12 September 2006 |
A very narrow gyrosynchrotron spectrum during a solar flare
1
Centro de Rádio Astronomia e Astrofísica Mackenzie, R. da Consolação 896, 01302-907 São Paulo, SP, Brazil e-mail: guigue@craam.mackenzie.br
2
Instituto Nacional de Pesquisas Espaciais, São José dos Campos, Brazil
3
Institute of Applied Physics, University of Bern, Bern, Switzerland
Received:
28
October
2005
Accepted:
13
June
2006
During the rising phase of the radio burst of August 30, 2002, at
∼1328 UT a short pulse with a duration of approximately 4 s was
observed. Here we present a multiwavelength analysis, including
microwave and X-ray. Its background-subtracted radio spectrum ranges only
from 2.5 to 12 GHz with a maximum flux density of approximately 900 s.f.u. at
7 GHz and a steep optically thin spectral index . The hard
X-ray pulse emission above the background in the range of 10–150 keV
observed by RHESSI is coincident in time with the microwave
observation. Hard X-ray images reveal very compact (~
) footpoint sources. A distribution of accelerated
electrons represented by a double power law, with
and
,
was used to compute the expected gyrosynchrotron and thick target
bremsstrahlung fluxes of a homogeneous source. We interpret the very steep
electron index above the energy break to represent a high energy cutoff. With
these parameters, our results reproduce the observations well.
Nevertheless, they pose the still unanswered question about the mechanism that has
slectively accelerated these electrons.
Key words: Sun: activity / Sun: flares / Sun: radio radiation
© ESO, 2006
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