HR: 16:45h
AN: SH54A-06    [Abstracts]
TI: Suggested Evidence for Coherent Synchrotron Microwaves by Microbunching Instability in a Solar Burst
AU: * Kaufmann, P
EM: kaufmann@craam.mackenzie.nr
AF: CRAAM, Universidade Presbiteriana Mackenzie, Rua Consolacão 893, São Paulo, SP 01302-907 Brazil
AU: * Kaufmann, P
EM: kaufmann@craam.mackenzie.nr
AF: CCS, Universidade Estadual de Campinas, Cidade Universitária Zeferino Vaz, Campinas, SP 13083-970 Brazil
AU: Raulin, J
EM: raulin@craam.mackenzie.br
AF: CRAAM, Universidade Presbiteriana Mackenzie, Rua Consolacão 893, São Paulo, SP 01302-907 Brazil
AB: The presence of solar flare submm-wave spectral emission component peaking in the THz range simultaneous to the well-known microwaves component, has been recently reported. It was particularly well observed in the November 4, 2003 large flare by the Solar Submillimeter-wave Telescope, El Leoncito, Argentina Andes, bringing serious difficulties for interpretation using existing models. The largest measured fluxes were of about 12,000 and 21,000 solar flux units (sfu) at 212 and 405 GHz, respectively. The source remained remarkably stable in space (within 15 arcseconds). Burst size smaller than about 10 arcseconds was evaluated, which imply in brightness temperatures larger than about 9-2 10⁶ K, at 200 and 400 GHz, indicating the emission from an optically thick non-thermal source. Intense microwaves were observed by the Owens Valley Solar Array, CA, USA, in the range 2-20 GHz, exhibiting spectral maxima in the range 15-19 GHz for different time structures. Peak flux of about 45,000 sfu determined at about 18 GHz was considerably larger than the THz component extrapolated down to 18 GHz (being of the order of 1,000 sfu). The fluxes became equal for the microwave and THz components at about 80-100 GHz. Spectral peaks at different frequencies may arise from different populations electrons accelerated, although there are no evidence to support this assumption. However the simultaneous presence of a double spectral component, at microwaves and at submillimeter waves, added to characteristics of the bursting features at both ranges, have striking similarities to coherent synchrotron radiation (CSR) produced at microwaves by high energy electron beams ( E > 100 MeV) in accelerators undergoing microbunching instabilities. This phenomenon is well known, although the super-radiant cm-mm wavelength CSR bursting mechanism is not fully understood. The THz solar flare component might due to incoherent synchrotron emission, produced by bunches of electrons, represented by the impulsive burst time structures. CSR is produced when the electron beam is submitted to a density modulation on the scale of the order or smaller than the emitting wavelength, originating microbunches, emitting power proportional to the incoherent component power squared. In laboratory accelerators this is accomplished submitting the electron beam to repetitive magnetic undulations, modifying the bunch shape, causing the microbunching instability. Models predict the creation of microbunching by the interaction of electron beams with its own synchrotron radiation, which amplifies itself via coherent emission. In the fine magnetic structures of solar active regions it is not difficult to conceive the presence of magnetic chicanes traversed by the accelerated bunches of electrons. Only a small fraction of the total number of particles accelerated undergoing microbunch instability would be needed to produce a substantial broadband coherent emission enhancement in the cm-mm wavelength range. The solar burst CSR reduces for smaller wavelengths, where the condition for instability vanishes. Rapid periodic bursts, with amplitude and frequency of occurrence increasing with the number of electrons in the beam (for larger intensities) are observed in accelerators and in solar bursts. They might be signatures of microbunching instabilities enhanced by wave-particle interaction. This suggested interpretation of solar flare emission require the complete knowledge of the spectrum into the THz range, which usually is not known for most of bursts.
DE: 0654 Plasmas
DE: 7514 Energetic particles (2114)
DE: 7519 Flares
DE: 7534 Radio emissions
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2005 Joint Assembly