The configuration of simple short-duration solar microwave bursts

¹ Astronomy Department, University of Maryland, College Park, MD 20742, USA e-mail: kundu@astro.umd.edu
² Section of Astrogeophysics, Physics Department, University of Ioannina, Ioannina 45110, Greece e-mail: anindos@cc.uoi.gr
³ Institute of Solar-Terrestrial Physics, Lermontov St. 126, Irkutsk 664033, Russia e-mail: grechnev@iszf.irk.ru

Corresponding author: A. Nindos, anindos@cc.uoi.gr

Received: 7 October 2003
Accepted: 2 March 2004

Abstract

Using data from the Nobeyama Radioheliograph (NoRH) we study the source configuration of four simple short-duration 17 and 34 GHz bursts which have also been observed partially by the Yohkoh Soft X-ray Telescope (SXT). Two events are consistent with a single flaring loop configuration. In one of them the flaring loop is resolved in the SXT images. We derive a self-consistent model for this event by comparing the radio observations with gyrosynchrotron model loop calculations. Our best-fit model is able to reproduce both the observed flaring loop shape as well as the fluxes and structures of the radio emission at the peak of the event. The flaring loop is relatively small having a footpoint separation of 16´´ and maximum height of 7.7´´. The variation of the magnetic field along the loop is small (800 G at the footpoints and 665 G at loop top) and the loop is filled with electrons with energies up to 10 MeV. The other two bursts show two radio sources; one source being cospatial with a compact bright soft X-ray loop associated with a patch of parasitic magnetic polarity whose photospheric magnetic flux increases before the flares while the other source is not prominent at any other wavelength range. The two sources are connected with diffuse loop-like soft X-ray emission. We infer that these bursts originate from the interaction of two sets of loops with different sizes. Therefore the simple short duration microwave bursts we studied do not always appear in the same configuration. Contrary to previous results not all of them appear as single-loop events. It is possible that some events are caused by two interacting loops.