STRONG INTRADAY VARIABILITY IN THE SOUTHERN BLAZAR PKS-0537-441 AT 1.42 GHZ

Results of intraday variability observations with a sampling of approx imately 20 minutes of the southern blazars PKS 0521-365 and PKS 0537-4 41 at 1.42 GHz are presented. PKS 0521-365 did not display flux densit y variability whilst PKS 0537-441 showed strong fluctuations with a ma jor out-burst towards J.D. 2449011 caracterized by a fluctuation index of approximately 15%, variability amplitudes of approximately 45% and time scales of approximately 10(4)s. After a discussion of possible s cenarios for such kind of variability, this extremely violent behaviou r is interpreted in terms of strong scattering by compact ionized stru ctures in the interstellar medium. The physical properties of the refr actors are estimated from the observed light curves, and a brief discu ssion about the possible origin of these objects is presented.