EDP Sciences Journals List
Advanced Search
Subscriber Authentication Point
Home All issues Volume 396/2 Article
Free access article

Issue A&A
Volume 396, Number 2, December III 2002
Page(s) 683 - 692
Section The Sun
DOI http://dx.doi.org/10.1051/0004-6361:20021431



A&A 396, 683-692 (2002)
DOI: 10.1051/0004-6361:20021431

Prolonged millimeter-wave radio emission from a solar flare near the limb

S. Pohjolainen1, 2, J. Hildebrandt3, M. Karlický4, A. Magun5 and I. M. Chertok6

1  Tuorla Observatory, Väisälä Institute for Space Physics and Astronomy, 21500 Piikkiö, Finland
2  Observatoire de Paris, DASOP, 92195 Meudon, France
3  Astrophysical Institute Potsdam, 14482 Potsdam, Germany
4  Astronomical Institute Ondrejov, 25165 Ondrejov, Czech Republic
5  Institute of Applied Physics, 3012 Bern, Switzerland
6  IZMIRAN, Russian Academy of Sciences, Troitsk, Moscow Region, 142190 Russia

(Received 3 November 2000 / Accepted 26 September 2002)

Abstract
We present a multi-wavelength analysis of a gradual radio flare on June 27, 1993 which showed emission at millimeter waves long after the soft X-ray flux had peaked. The radio flare located at S12 E75 was associated with a GOES class M3.6 flare that lasted for more than one hour and hard X-ray emission during the rising phase of the soft X-ray/radio emission. The maximum radio flux density at 35 GHz was 60 sfu, but the calculated thermal bremsstrahlung flux from the GOES soft X-rays was less than half of that. The possible explanations for this prolonged millimeter wave emission could be accelerated high-energy electrons gyrating along the field-lines (nonthermal gyrosynchrotron emission) or thermal bremsstrahlung from evaporating chromospheric warm and dense plasma (cool enough to go undetected by GOES), or a mixture of these. Our model calculations show that even an inhomogeneous source containing both kinds of particles would not be able to produce such a spectral shape. A second source with extremely high electron densities ( >10 16 m -3), large source dimensions ( >10 15 m 2), and very low temperatures ( <10 6 K) must be assumed to explain the observed radio spectra.


Key words: Sun: chromosphere -- Sun: corona -- Sun: flares -- Sun: radio radiation -- X-rays: general

Offprint request: S. Pohjolainen, spo@astro.utu.fi




© ESO 2002


What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.
  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.