A geometrical interpretation for the properties of multiband optical
  variability of the blazar S5 0716+714
  We present the results of multiband observations of the blazar S5 0716+714
intra-night variability performed during 23 nights in the period from 04.2014
through 04.2015. The bluer-when-brighter trend is detected in both intra- and
inter-night data. We assume that the jet component crossing the region where
the medium becomes transparent to the optical radiation forms almost all
optical emission of S5 0716+714. Deviations of some parts of the component from
the general trajectory of the component can cause the Doppler factor of these
parts to increase. Various maximum Doppler factors achieved by these parts of
the component and different volumes occupied by them with the concave
synchrotron self-absorption spectrum result in both the observed various color
index behavior in variability and explain the absence of dependence of the
bluer-when-brighter behavior on the object magnitude. We estimated spectral
maximum frequency $\nu_\text{m}\approx\left( 0.6-1.7\right)\cdot10^{14}$ Hz
from intra- and inter-night data. Assuming that the size of emitting region is
comparable with the gravitational radius of a black hole with a mass of
$5\cdot10^8$ solar masses, the magnetic field obtained from synchrotron
self-absorption is $B\sim10^2-10^4$ G, which corresponds to the values of other
independent estimations. The obtained values of $\nu_\text{m}$ and $B$ confirm
our assumption about the nature of the blazar S5 0716+714 region radiating in
the optical range.
