2006/11/13 by L. Fuhrmann, T. P. Krichbaum, Fuhrmann, L. +21
Physics and Astronomy · #Astrophysics (astro-ph) #FOS: Physical sciences #astro-ph
paper · pdf · doi:10.48550/arxiv.astro-ph/0611391
6 pages, 3 figures, to appear in the proceedings of the 8th EVN symposium held in Torun, Poland, September 2006
arxiv created 2006/11/13 · arxiv updated 2009/12/01
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 signatures of the inverse-Compton catastrophe. Here we present first results obtained from a combined analysis 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 variability 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 intrinsic 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 lower 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.