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The BL Lac object S5 0716+71 was observed in a global multi-frequencycampaign to search for rapid and correlated flux density variability andsignatures of an inverse-Compton (IC) catastrophe during the states of extremeapparent brightness temperatures. The observing campaign involved simultaneousmonitoring at radio to IR/optical wavelengths centered around a 500-ks INTEGRALpointing (November 10-17, 2003). We present the combined analysis and resultsof the cm- to sub-mm observations including a detailed study of the inter- tointra-day variability and spectral characteristics of 0716+714. We furtherconstrain the variability brightness temperatures (T_B) and Doppler factors(delta) comparing the radio-bands with the hard X-ray emission (3-200 keV).0716+714 was in an exceptionally high state (outburst) and different (slower)phase of short-term variability. The flux density variability in the cm- tomm-bands is dominated by a correlated, ~4 day time scale amplitude increase ofup to ~35% systematically more pronounced towards shorter wavelengths. Thiscontradicts expectations from standard interstellar scintillation (ISS) andsuggests a source-intrinsic origin of the variability. The derived lower limitsto T_B exceed the 10^12 K IC-limit by up to 3-4 orders of magnitude. Assumingrelativistic boosting, we obtain robust and self-consistent lower limits ofdelta >= 5-33, in good agreement with delta_VLBI obtained from VLBI studies andthe IC-Doppler factors delta_IC > 14-16 obtained from the INTEGRAL data. Sincea strong contribution from ISS can be excluded and a simultaneous ICcatastrophe was not observed, we conclude that relativistic Doppler boostingnaturally explains the apparent violation of the theoretical limits withinstandard synchrotron-self-Compton (SSC) jet models of AGN.

astronomy and astrophysics

Testing the inverse-Compton catastrophe scenario in the intra-day  variable blazar S5 0716+71, III. Rapid and correlated flux density  variability from radio to sub-mm bands