  We investigate quasi-periodic coronal pulsations during the decay phase of an
X 3.2 class flare on 14 May 2013, using soft X-ray data from the RHESSI
satellite. Periodogram analyses of soft X-ray light curves show that 53 s and
72 s periods co-exist in the 3-6, 6-12 and 12-25 KeV energy bands. Considering
the typical length of the flaring loop system and observed periodicities, we
find that they are associated with multiple (first two harmonics) of fast
magnetoacoustic sausage waves. The phase relationship of soft X-ray emissions
in different energy bands using cross-correlation technique show that these
modes are standing in nature as we do not find the phase lag. Considering the
period ratio, we diagnose the local plasma conditions of the flaring region by
invoking MHD seismology. The period ratio P1/2P2 is found to be 0.65, which
indicates that such oscillations are most likely excited in longitudinal
density stratified loops.
