  Quasi-periodic pulsations (QPP) are common in solar flares and are now
regularly observed in stellar flares. We present the detection of two different
types of QPP signals in the thermal emission light curves of the X9.3 class
solar flare SOL2017-09-06T12:02, which is the most powerful flare of Cycle 24.
The period of the shorter-period QPP drifts from about 12 to 25 seconds during
the flare. The observed properties of this QPP are consistent with a sausage
oscillation of a plasma loop in the flaring active region. The period of the
longer-period QPP is about 4 to 5 minutes. Its properties are compatible with
standing slow magnetoacoustic oscillations, which are often detected in coronal
loops. For both QPP signals, other mechanisms such as repetitive reconnection
cannot be ruled out, however. The studied solar flare has an energy in the
realm of observed stellar flares, and the fact that there is evidence of a
short-period QPP signal typical of solar flares along with a long-period QPP
signal more typical of stellar flares suggests that the different ranges of QPP
periods typically observed in solar and stellar flares is likely due to
observational constraints, and that similar physical processes may be occurring
in solar and stellar flares.
