Peak of spectral energy distribution plays an important role in intra-day variability of blazars?

Abstract

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.