  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 June 2000 to July 2012. Here we focus on
the multi-wavelength 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 year span of these
observations.
