Rapid and correlated variability of blazar S5 0716+71 from radio- to sub-mm bands

Landessternwarte Heidelberg-Konigsstuhl, Heidelberg, G ermany The BL Lac object S5 0716+71 was target of a coordinated and global multi-frequency campaign to search for rapid and correlated variability and signatur es of the inverse-Compton catastrophe. Here we present first results obtained from a combined analys is of the cm- to sub-mm observations over a period of seven days aiming at a detailed study of the intra- to inter-day variability characteristics and to obtain constraints on the variabili ty brightness temperatures and Doppler factors comparing the radio data with the high energy emission recorded by INTEGRAL. A more detailed description of the whole cm- to sub-mm observations and our analysis/results will be presented in a forthcoming paper. Our analysis reveals the source to be in a particular short-term variability phase when compared to the past with a correlated & 4 day time scale amplitude increase of up to 35%, which is systematically more pronounced towards higher frequencies. The obtained frequency dependent variability amplitudes and time lags contradict expectations from interstellar scintillation and strongly suggest a source i ntrinsic origin of this inter-day variability. A 7-day spectral evolution study indicate time-variable synchrotron self-absorption and expansion of the emission region, consistent with standard models. Assuming relativistic boosting, our different estimates of the Doppler factor yield robust l ower limits of Dvar,IC > 5-22 using the inverse-Compton limit and Dvar,eq > 8-33 using the equipartition argument. Although high, these values are in good agreement with Doppler factors obtained from recent VLBI studies and from the inverse-Compton Doppler factors DIC > 14-16 derived with the X-ray emission seen by INTEGRAL at 3-200 keV.