mercredi 1er avril 2009, par Tim Bastian (National Radio Astronomy Observatory, Charlottesville, VA, USA)
Lundi 6 avril 2009 à 11h00 , Lieu : Salle de confĂ©rence du bât. 17
Oscillations and quasi-periodic pulsations (QPPs) have been observed in the radio and X-ray emission from solar flares for many years. Generally speaking, radio QPPS have been attributed to nonlinear, self-organizing wave-wave or wave-particle interactions in the case of coherent emission, and to modulation of the source parameters in the case of incoherent emission. In particular, incoherent gyrosynchrotron emission at centimeter wavelengths is typically attributed to variations in the coronal magnetic field due to the excitation of MHD modes and/or the modulation of the acceleration and injection of energetic electrons into the source. This talk concerns some recent work on an impulsive flare that displayed QPPs in both its microwave and HXR emission. Observations by the Nobeyama Radioheliograph, the Nobeyama Polarimeters, the Owens Valley Solar Array, and the Ramaty High Energy Solar Spectroscopic Imager were obtained and a Fourier analysis of the radio and X-ray data was performed. Together with observations of the time variability of the radio polarization and spectral index, these data show that MHD oscillations are unlikely to play a significant role in modulating the source ; quasi-periodic acceleration and injection of the energetic electrons is the more likely explanation.
