Decimetric radio dot emissions

¹ National Space Research Institute (INPE), São José dos Campos, SP, Brazil
² Astronomical Institute of the Academy of Sciences of the Czech Republic, 25165 Ondřejov, Czech Republic e-mail: hana@asu.cas.cz
³ Institute of Research and Development (IP&D - UNIVAP), São José dos Campos, SP, Brazil

Received: 30 April 2007
Accepted: 6 September 2008

Abstract

Context. We study a rare type of solar radio bursts called decimetric dot emissions.

Aims. In the period 1999-2001, 20 events of decimetric dot emissions observed by the Brazilian Solar Spectroscope (BSS) in the frequency range 950-2640 MHz are investigated statistically and compared with radio fine structures of zebras and fibers.

Methods. For the study of the spectral characteristics of the dot emissions we use specially developed Interactive Data Language (IDL) software called BSSView and basic statistical methods.

Results. We have found that the dm dot emissions, contrary to the fine structures of the type IV bursts (i.e. zebras, fibers, lace bursts, spikes), are not superimposed on any background burst emission. In the radio spectrum, in most cases the dot emissions form chains that appear to be arranged in zebra patterns or fibers. Because some zebras and fibers, especially those observed with high time and high spectral resolutions, also show emission dots (but superimposed on the background burst emission), we compared the spectral parameters of the dot emissions with the dots being the fine structure of zebras and fibers. For both these dots, similar spectral characteristics were found. Some similarities of the dot emissions can be found also with the lace bursts and spikes. For some events the dot emissions show structural evolution from patterns resembling fibers to patterns resembling zebras and vice versa, or they evolve into fully chaotic patterns.

Conclusions. For the first time, we present decimetric dot emissions that appear to be arranged in zebra patterns or fibers. We propose that these emissions are generated by the plasma emission mechanism at the locations in the solar atmosphere where the double resonance condition is fulfilled.