A very narrow gyrosynchrotron spectrum during a solar flare
Centro de Rádio Astronomia e Astrofísica Mackenzie, R. da Consolação 896, 01302-907 São Paulo, SP, Brazil e-mail: email@example.com
2 Instituto Nacional de Pesquisas Espaciais, São José dos Campos, Brazil
3 Institute of Applied Physics, University of Bern, Bern, Switzerland
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