Peak of spectral energy distribution play an important role in intra-day
  variability of Blazars?
  Blazars can be divided into two sub-classes namely high energy and low energy
peaked blazars. In spectral energy distribution, the first synchrotron hump of
the former class peaks in UV/X-rays and in IR/optical bands for the latter
class. The peak of the spectral energy distribution seems to be responsible for
variability properties of these classes of blazars in X-ray and optical bands.
Since, in low energy peaked blazars, the X-ray bands lies well below the
synchrotron hump, one expects that the highest energy electrons available for
the synchrotron emission would have slower effect of variability on X-ray
intra-day timescale. In this paper, by taking the advantage of a sample of 12
low energy peaked blazars with total 50 observations from XMM$-$Newton since
its launch, we confirm that this class is less variable in X-ray bands. We
found that out of 50 observational light curves, genuine intra-day variability
is present in only two of light curves i.e 4%. Similar results we obtained from
our earlier optical intra-day variability studies of high energy peaked blazars
where out of 144 light curves, only genuine intra-day variability was detected
in 6 light curves i.e ~ 4%. Since, X-ray bands lie below the peak of the
spectral energy distribution of LSPs where inverse Compton mechanism is
dominating rather than synchrotron radiation at the peak of the optical band,
leads to slower variability in the X-ray bands. Hence, reducing their intra-day
variability in X-ray bands as compared to the variability in optical bands.
