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 .