  Solar flares often display pulsating and oscillatory signatures in the
emission, known as quasi-periodic pulsations (QPP). QPP are typically
identified during the impulsive phase of flares, yet in some cases, their
presence is detected late into the decay phase. Here, we report extensive fine
structure QPP that are detected throughout the large X8.2 flare from 2017
September 10. Following the analysis of the thermal pulsations observed in the
GOES/XRS and the 131 A channel of SDO/AIA, we find a pulsation period of ~65 s
during the impulsive phase followed by lower amplitude QPP with a period of
~150 s in the decay phase, up to three hours after the peak of the flare. We
find that during the time of the impulsive QPP, the soft X-ray source observed
with RHESSI rapidly rises at a velocity of approximately 17 km/s following the
plasmoid/coronal mass ejection (CME) eruption. We interpret these QPP in terms
of a manifestation of the reconnection dynamics in the eruptive event. During
the long-duration decay phase lasting several hours, extended downward
contractions of collapsing loops/plasmoids that reach the top of the flare
arcade are observed in EUV. We note that the existence of persistent QPP into
the decay phase of this flare are most likely related to these features. The
QPP during this phase are discussed in terms of MHD wave modes triggered in the
post-flaring loops.
