  We observe intensity oscillations along coronal fan loops associated with the
active region AR 11428. The intensity oscillations were triggered by blast
waves which were generated due to X-class flares in the distant active region
AR 11429. To characterise the nature of oscillations, we created time-distance
maps along the fan loops and noted that the intensity oscillations at two ends
of the loops were out of phase. As we move along the fan loop, the amplitude of
the oscillations first decreased and then increased. The out-of-phase nature
together with the amplitude variation along the loop implies that these
oscillations are very likely to be standing waves. The period of the
oscillations are estimated to be $\sim$27 min, damping time to be $\sim$45 min
and phase velocity projected in the plane of sky $\sim$ 65-83 km s$^{-1}$. The
projected phase speeds were in the range of acoustic speed of coronal plasma at
about 0.6 MK which further indicates that these are slow waves. To best of our
knowledge, this is the first report on the existence of the standing slow waves
in non-flaring fan loops.
