Astron. Astrophys. 333, 1034-1042 (1998)

Intermediate drift bursts and the coronal magnetic field

Arnold O. Benz ¹ and Gottfried Mann <sup>2

1</sup> Institute of Astronomy, ETH-Zentrum, CH-8092 Zürich, Switzerland
² Astrophysikalisches Institut, Observatorium für solare Radioastronomie, D-14473 Potsdam, Germany

Received 8 December 1997 / Accepted 27 January 1998

Abstract

We have analyzed 12 decimetric continuum (type IV) events during solar flares showing intermediate drift (IMD) fine structures in the 1 - 3 GHz band. This is the first time IMD patterns have been reported above 1 GHz and that the full spectrum of both continuum and IMD bursts has been covered. The IMD pattern was usually shifted to higher frequency and tends to occur later than the continuum. Average drift rates of IMD bursts per event were found by cross-correlation yielding = -0.167 to -0.046 s^-1. The average second derivative of individual IMD bursts expressed as is 0.42 to 4.19. Normalized by the mean frequency, these high-frequency IMD bursts are found to be identical in their characteristics with this type of bursts below 1 GHz. The derived burst parameters require an important change in one of the two existing theories.

Key words: Sun: corona Sun: magnetic fields Sun: flares Sun: radio radiation

Send offprint requests to: A.O. Benz

Contents

• 1. Introduction
• 2. Observations
  • 2.1. The location of IMD bursts in the spectrogram
  • 2.2. Properties of individual IMD bursts
  • 2.3. Average properties of IMD groups
• 3. Theory and discussion
  • 3.1. Alfvén wave model with plasma emission
  • 3.2. Alfvén wave model with electron cyclotron maser emission
  • 3.3. Whistler wave model
• 4. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1998

Online publication: April 28, 1998

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