High-speed photometry of V404 Cygni in outburst

High-speed photometric observations are presented of the optical counterpart of the X-ray transient GS 2023 + 338 (V404 Cygni) obtained during the decline from a major outburst. The low-frequency flickering previously reported in X-rays, optical, and radio waves is confirmed. From four night's coverage in September 1989, no evidence is found in the light curve for a unique coherent period. However, transient broad features are observed in the power spectra at periods in the range of 3-10 minutes. Similar features are commonly seen in the optical light curves of erupting dwarf novae; they may be a characteristic signature of disk accretion onto any type of compact star. 35 refs