SIMBAD references

We have undertaken a nearly simultaneous optical/UV and X-ray variability study of the flat spectrum radio quasar, 3C 273 using data available from the XMM-Newton satellite mission from 2000 June to 2012 July. Here, we focus on the multiwavelength flux variability on both intra-day and long time-scales of this very well known radio-loud source. We found high flux variability over long time-scales in all bands for which observations were made. The optical/UV variability amplitude was more than twice than that in the X-ray bands. There is some frequency dependence of the variability in optical/UV bands in the sense that the variability amplitude increases with increasing frequency; however, the X-ray emissions disagree with this trend as the variability amplitude decreases from soft to hard X-ray bands. On intra-day time-scales 3C 273 showed small amplitude variability in X-ray bands. A hardness ratio analysis in the X-ray regime indicates that the particle acceleration mechanism dominates the cooling mechanism during most of the ∼ 12 yr span of these observations.