3.5 Impulsive microwave bursts
Simultaneously, this same electron population, in conjunction with strong chromospheric
magnetic fields, produces gyro-synchrotron radiation that can be observed from the ground using
radiotelescopes (see, e.g. Pick et al., 1990). There is a very good time correlation between the
hard X-ray bursts and impulsive microwave radiation, in particular for the higher frequencies
beyond 1 GHz. The spectrum is a broadband continuum with peak intensities at some tens of
GHz for the strongest events. For detailed information see, e.g. Benka and Holman (1992)
and Holman (2003).
Very recently, a new kind of rapid solar spikes (100 – 500 ms) was observed at submillimetric waves (212
and 405 GHz) by the new Solar Submm-wave Telescope (SST) by Kaufmann et al. (2003
). They suggest
that these pulse bursts might be representative of an important early signature of CMEs, but a consistent
explanation is still lacking. During the November 4, 2003 flare, a further new microwave burst spectral
component was observed by Kaufmann et al. (2004), that apparently peaks in the THz to infrared range.
The origin of these bursts is still unclear. This type of radio bursts might be common to many solar events,
but observing them requires new techniques that are able to bridge the gap between electronics and
photonics.
