Locating the gamma-ray emission site in Fermi/LAT blazars. II
  Multifrequency correlations
  In an attempt to constrain and understand the emission mechanism of gamma
rays, we perform a cross-correlation analysis of 15 blazars using light curves
in millimetre, optical and gamma rays. We use discrete correlation function and
consider only correlations significant at 99 per cent level. A strong
correlation was found between 37 and 95 GHz with a near-zero time delay in most
of the sources, and ~1 month or longer in the rest. A similar result was
obtained between the optical and gamma-ray bands. Of the 15 sources, less than
50 per cent showed a strong correlation between the millimetre and gamma-ray or
millimetre and optical bands. The primary reason for the lack of statistically
significant correlation is the absence of a major outburst in the millimetre
bands of most of the sources during the 2.5 yr time period investigated in our
study. This may indicate that only the long-term variations or large flares are
correlated between these bands. The variability of the sources at every
waveband was also inspected using fractional rms variability. The fractional
rms variability displays an increase with frequency reaching its maximum in the
gamma rays.
