A very narrow gyrosynchrotron spectrum during a solar flare

Giménez de Castro, C.G., Costa, J.E.R., Silva, A.V.R., Simoes, P.J.A. , Correia, E. and Magun, A. (2006) A very narrow gyrosynchrotron spectrum during a solar flare. Astronomy and Astrophysics, 457(2), pp. 693-697. (doi: 10.1051/0004-6361:20054438)

Abstract

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 α ∼ 8. 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 (∼10) footpoint sources. A distribution of accelerated electrons represented by a double power law, with δE < 250 keV = 5.3 and δE ≥ 250 keV = 13, 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.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Simoes, Dr Paulo
• Authors: Giménez de Castro, C.G., Costa, J.E.R., Silva, A.V.R., Simoes, P.J.A., Correia, E., and Magun, A.
• College/School: College of Science and Engineering > School of Physics and Astronomy
• Journal Name: Astronomy and Astrophysics
• Publisher: EDP Sciences
• ISSN: 0004-6361
• ISSN (Online): 1432-0746
• Copyright Holders: Copyright © 2006 ESO
• First Published: First published in Astronomy and Astrophysics 457(2):693-697
• Publisher Policy: Reproduced in accordance with the copyright policy of the publisher