Radio evidence on shock wave formation in the solar corona
A. Klassen 1,
H. Aurass 1,
K.-L. Klein 2,
A. Hofmann 1 and
G. Mann 1
Received 27 August 1998 / Accepted 2 December 1998
In order to investigate the formation of radio emitting shock waves above flaring active regions, we combine spectral and imaging observations of type II radio events with X-ray imaging and full-Sun observations and, in one case, with the extrapolated magnetic field configuration in the corona. We confirm and extend earlier findings that type II bursts are emitted above active region loops seen in soft X-ray images. Sources at successively lower frequencies are non-radially displaced from the axis of the active region loops. Two new radio features identified in high resolution spectrograms establish a possible link between the type II emission and the preceding activity in the underlying corona:
It is concluded that the type II burst is related to a plasma jet or a blast wave that originates in closed magnetic structures in the active region, and is first recognized during the early impulsive phase (between the onset and main maximum of the hard X-ray emission). This disturbance becomes or launches a shock wave when it attains the summit of these structures. The shock is refracted into overlying field regions, where it becomes visible through the type II emission.
Key words: shock waves Sun: corona Sun: flares Sun: magnetic fields Sun: radio radiation
Send offprint requests to: A. Klassen (email@example.com)
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© European Southern Observatory (ESO) 1999
Online publication: March 1, 1999