Detectability of optical transients with timescales of sub-seconds

We search for optical transient sources with durations of $\sim 0.1$ to $\sim 1.3$ s using a dataset obtained in the Organized Autotelescopes for Serendipitous Event Survey (OASES) observation campaign. Since the OASES observations were carried out using two independent wide-field and high-cadence observation systems monitored the same field simultaneously, the obtained dataset provides a unique opportunity to develop a robust detection method for sub-second optical transients. In the dataset of a selected field around the ecliptic and the Galactic plane, we find no astronomical event candidate that satisfies our detection criteria. From the non-detection result, we derive an upper limit on the event rate of sub-second transients around the ecliptic and the Galactic plane for the first time, obtaining $\sim 0.090$ and $\sim 0.38~{\rm hr^{-1}~deg^{-2}}$ for $m = 12$ and 13 Vmag, respectively. In addition, future prospects of the sub-second scale transient event surveys are discussed.