  Very long-periodic pulsations during preflare phases (preflare-VLPs) have
been detected in the full-disk solar soft X-Ray (SXR) flux (see Tan et al.
2016). They may be regarded as precursors to solar flares and may help us
better understand the trigger mechanism of solar flares. In this letter, we
report a preflare-VLP event before the onset of an M1.1 circular-ribbon flare
on 2015 October 16. It was simultaneously observed in Halpha, SXR, and extreme
ultraviolet (EUV) wavelengths, which were recorded by the NVST, GOES, EVE, and
AIA respectively. The preflare-VLP is identified as the repeat and
quasi-periodic pulses in light curves during preflare phase, which might be
modulated by LRC-circuit oscillation in the current-carrying plasma loop. The
quasi-periodicity can be determined from the Fourier power spectrum with Markov
chain Monte Carlo (MCMC)-based Bayesian (e.g., Liang et al. 2020), such as ~9.3
minutes. We present the first report of a preflare-VLP event in the local
Halpha line and EUV wavelength, which could be considered a precursor of a
solar flare. This finding should therefore prove useful for the prediction of
solar flares, especially for powerful flares.
