2023NatAs...7.1108J

Hyperluminous optical-ultraviolet flares have been detected in gamma-ray bursts and the luminosity record was held by naked-eye event GRB 080319B. Such flares are widely attributed to internal shock or external reverse shock radiation. Here, with a new method developed to derive reliable photometry from saturated sources of Swift/UVOT, we carry out time-resolved analysis of the initial white-band 150 s exposure of GRB 220101A, a burst at a redshift of 4.618, and report a rapidly evolving optical-ultraviolet flare with a high absolute AB magnitude of -39.4 ± 0.2. In contrast to GRB 080319B, the temporal behaviour of this new flare does not trace the gamma-ray activity. Instead of either internal shocks or reverse shock, this extremely energetic optical-ultraviolet flare is most likely to originate from the refreshed shocks induced by the late-ejected extremely energetic material catching up with the earlier-launched decelerating outflow. This finding reveals the diverse origins of the extremely energetic optical-ultraviolet flares and demonstrates the necessity of high-time-resolution observations at early times.