  We report the detection of multiple quasi-periodic pulsations (QPPs) observed
during the flaring activity of KIC 8414845, a young, active solar-type star
observed by the Kepler mission launched by NASA. We analyzed the QQP signal
using a data-driven, nonparametric method called singular spectrum analysis
(SSA), which has never been utilized previously for analyzing solar or stellar
QPPs. Because it is not based on a prescribed choice of basis functions, SSA is
particularly suitable for analyzing nonstationary, nonlinear signals such as
those observed in QPPs during major flares. The analysis has revealed that the
apparent anharmonic shape of the QPP in this superflare results from a
superposition of two intrinsic modes of periods of 49 min and 86 min, which
display quasi-harmonic behaviors and different modulation patterns. The two
reconstructed signals are consistent with slow-mode transverse and/or
longitudinal magnetohydrodynamic oscillations excited in a coronal loop
inducing periodic releases of flaring energy in a nearby loop through a
mechanism of repetitive reconnection. The peculiar amplitude modulation of the
two modes evinced by SSA favors the interpretation of the observed QPP pattern
as due to the excitation in a coronal loop of the second harmonic of a standing
slow-mode magnetoacoustic oscillation and a global kink oscillation
periodically triggering magnetic reconnection in a nearby loop. Concurrent
interpretations cannot however be ruled out on the basis of the available data.
