A decade of joint MOJAVE-Fermi AGN monitoring: localisation of the
  gamma-ray emission region
  Within the MOJAVE VLBA program (Monitoring of Jets in AGN with VLBA
Experiments), we have accumulated observational data at 15 GHz for hundreds of
jets in $\gamma$-ray bright active galactic nuclei since the beginning of the
Fermi scientific observations in August 2008. We investigated a time delay
between the flux density of AGN parsec-scale radio emission at 15 GHz and
0.1$-$300 GeV Fermi LAT photon flux, taken from constructed light curves using
weekly and adaptive binning. The correlation analysis shows that radio is
lagging $\gamma$-ray radiation by up to 8 months in the observer's frame, while
in the source frame, the typical delay is about 2-3 months. If the jet radio
emission, excluding the opaque core, is considered, significant correlation is
found at greater time lags. We supplement these results with VLBI kinematics
and core shift data to conclude that the dominant high-energy production zone
is typically located at a distance of several parsecs from the central nucleus.
We also found that quasars have on average more significant correlation peak,
more distant $\gamma$-ray emission region from the central engine and shorter
variability time scale compared to those of BL Lacertae objects.
