  Quasi-periodic pulsations (QPPs), which usually appear as temporal pulsations
of the total flux, are frequently detected in the light curves of solar/stellar
flares. In this study, we present the investigation of non-stationary QPPs with
multiple periods during the impulsive phase of a powerful flare on 2017
September 06, which were simultane- ously measured by the Large-Yield
RAdiometer (LYRA) and the Hard X-ray Modula- tion Telescope (Insight-HXMT), as
well as the ground-based BLENSW. The multiple periods, detected by applying a
wavelet transform and Lomb-Scargle periodogram to the detrended light curves,
are found to be about 20-55 s in the Ly-alpha and mid-ultraviolet Balmer
continuum emissions during the flare impulsive phase. Similar QPPs with multi-
ple periods are also found in the hard X-ray emission and low-frequency radio
emission. Our observations suggest that the flare QPPs could be related to
nonthermal electrons accelerated by the repeated energy release process, i.e.,
triggering of repetitive magnetic reconnection, while the multiple periods
might be modulated by the sausage oscillation of hot plasma loops. For the
multi-periodic pulsations, other generation mechanisms could not be completely
ruled out.
