  To determine the location of the intra-day variable (IDV) emission region
within the jet of the BL Lac object S5 0716+714, a multi-epoch VSOP
polarization experiment was performed in Autumn 2000. To detect, image, and
monitor the short term variability of the source, three space-VLBI experiments
were performed with VSOP at 5 GHz, separated in time by six days and by one
day. Quasi-contemporaneous flux density measurements with the Effelsberg 100 m
radio telescope during the VSOP observations revealed variability of about 5%
in total intensity and up to 40% in linear polarization in less than one day.
Analysis of the VLBI data shows that the variations are located inside the VLBI
core component of 0716+714. In good agreement with the single-dish
measurements, the VLBI ground array images and the VSOP images, both show a
decrease in the total flux density of ~20 mJy and a drop of ~5 mJy in the
linear polarization of the VLBI core. During the observing interval, the
polarization angle rotated by about 15 degrees. No variability was found in the
jet. The high angular-resolution VSOP images are not able to resolve the
variable component and set an upper limit of <0.1 mas to the size of the core
component. From the variability timescales we estimate a source size of a few
micro-arcseconds and brightness temperatures exceeding 10^15 K. We discuss the
results in the framework of source-extrinsic (interstellar scintillation
induced) and source-intrinsic IDV models.
