Persistent 1.5s oscillations superimposed at a solar burst observed at two mm-wavelengths

Long-enduring quasi-periodic oscillations (1.5s) superimposed to a solar burst were observed simultaneously at two different mm-wavelengths (22 GHz and 44 GHz). The oscillations were present throughout the burst duration (about 10 min), and were delayed at 44 GHz with respect to 22 GHz by 0.3s. The relative amplitude of the oscillation was about 20 percent at 44 GHz and about 5 percent at 22 GHz. Interferometer measurements at 10.6 GHz indicated that the burst source was stable within 1 arcsec. The HeD3 line flare indicated two persistent small spots separated by about 10 arcsec. The 22/44 GHz burst position has good correspondence with the HeD3 spots' location. The oscillations displayed features which apprear to distinguish them from ultrafast time structures found in other bursts. One possible interpretation was suggested by assuming a modulation of the gyrosynchrotron emission of trapped electrons by a variable magnetic field on a double burst source, optically thin at 44 GHz and with an optical thickness of approximately 0.3 at 22 GHz