Multi-resolution wavelet analysis of high time resolution millimeter wavelength observations of solar bursts

By means of the wavelet representation of multi-resolution analysis, we stu dy millimeter wavelength (mm-w) radio solar bursts obtained at 48 GHz with high time resolution (less than or equal to8 ms), observed at Itapetinga (B razil). The multi-resolution analysis decomposes the signal locally both in time and in frequency. allowing us to identify the different temporal stru ctures which underlie the flux density time series and the transient phenom ena characteristic of solar bursts. The analysis was applied to the flux ti me profile of four solar bursts observed at a mm-w, studying separately the pre-flare, impulsive and post-flare phases when possible. We find that a w ide range of time scales contributes to the radio flux. The minimum time sc ale found for the impulsive phase is 32 ms, after which the noise dominates the emission the maximum is 8 s. Pre- and post-flare phases have a minimum time scale of 256 ms and a maximum between 1 to 8 s. Multi-resolution "spe ctral indexes", which are a measure of the self-similar behavior of the sig nal. are in some cases bigger for the impulsive phase than for the pre- and post-flare phases. We find that as the Aux becomes higher the contribution from shorter time scales is enhanced.