The objective of this project is to document the low frequency (frequency less than 1 GHz) characteristics of variable extragalactic radio sources. These data will be compared with the predictions of the various mechanisms which have been proposed for this activity. These mechanisms can be divided into: a) Intrinsic variability of a relativistically evolving source, and b) Extrinsic variability due to scattering or absorption in the intervening medium. In order to decide between the hypotheses, observations will be carried out to: a) Continue with the periodic measurements of the flux density of radio sources at low frequencies (318 MHz and 430 MHz), b) Obtain high resolution images of the sources at low frequencies (327 MHz) using Very Long Baseline Interferometry (VLBI), and c) Obtain low frequency (327 MHz) images of these sources at the Very Large Array (VLA). The data base will be augmented by data from a collaboration with other groups working at radio and optical wavelengths. The participation of undergraduate and graduate students in this project, which involves international cooperation and the use of modern and sophisticated techniques, represents for them challenging and rewarding opportunities.
