Radio to gamma-ray variability study of blazar S5 0716+714
  We present the results of a series of radio, optical, X-ray and gamma-ray
observations of the BL Lac object S50716+714 carried out between April 2007 and
January 2011. The multi-frequency observations were obtained using several
ground and space based facilities. The intense optical monitoring of the source
reveals faster repetitive variations superimposed on a long-term variability
trend at a time scale of ~350 days. Episodes of fast variability recur on time
scales of ~ 60-70 days. The intense and simultaneous activity at optical and
gamma-ray frequencies favors the SSC mechanism for the production of the
high-energy emission. Two major low-peaking radio flares were observed during
this high optical/gamma-ray activity period. The radio flares are characterized
by a rising and a decaying stage and are in agreement with the formation of a
shock and its evolution. We found that the evolution of the radio flares
requires a geometrical variation in addition to intrinsic variations of the
source. Different estimates yield a robust and self-consistent lower limits of
\delta > 20 and equipartition magnetic field B_eq > 0.36 G. Causality arguments
constrain the size of emission region \theta < 0.004 mas. We found a
significant correlation between flux variations at radio frequencies with those
at optical and gamma-rays. The optical/GeV flux variations lead the radio
variability by ~65 days. The longer time delays between low-peaking radio
outbursts and optical flares imply that optical flares are the precursors of
radio ones. An orphan X-ray flare challenges the simple, one-zone emission
models, rendering them too simple. Here we also describe the spectral energy
distribution modeling of the source from simultaneous data taken through
different activity periods.
