The uncorrelated long term gamma-ray and X-ray variability of blazars
  and its implications on disk-jet coupling
  We examine the long term (~10 years) gamma-ray variability of blazars
observed by EGRET and Fermi and find that for six sources the average flux
varied by more than an order of magnitude. For two of these sources (PKS
0208-512 and PKS 0528+134), there were extensive observations (at various
observing periods) by EGRET. Hence these dramatic variations are not due to a
single short time-scale flare, but reflect long term changes in the average
flux. Over the last twenty years, these two sources were also the target of
several X-ray observatories (e.g. ROSAT, ASCA, RXTE, BeppoSAX, Chandra, Suzaku,
XMM-Newton and Swift). While the ratios of the average gamma-ray fluxes between
EGRET and Fermi observations are 22.9 +/- 1.9 and 12.6 +/- 1.5, their estimated
2-10 keV X-ray flux do not show such dramatic variations. The X-ray emission
from such flat spectrum radio quasars (FSRQs) are believed to be due to
synchrotron self Compton, while gamma-rays originate from inverse
Comptonization of external soft photons from an accretion disk and/or broad
line region. We argue that in this scenario, the only explanation for the
uncorrelated variability is that there was an order of magnitude decrease in
the external soft photons, while the jet parameters remained more or less
constant. This result indicates that perhaps the accretion and jet processes
are not tightly coupled in these sources.
