An optical-ultraviolet flare with absolute AB magnitude of -39.4 detected in GRB 220101A

TL;DR

This paper reports the discovery of an extremely luminous optical-ultraviolet flare in GRB 220101A, with a magnitude of -39.4, likely originating from refreshed shocks, highlighting the diversity of origins for such energetic events.

Contribution

The study introduces a new method for reliable photometry of saturated sources and provides the first detailed analysis of a hyperluminous optical-ultraviolet flare in GRB 220101A, revealing a different origin from previous events.

Findings

Detected a hyperluminous optical-ultraviolet flare with magnitude -39.4.

The flare's behavior does not follow gamma-ray activity, unlike previous events.

The flare likely originates from refreshed shocks caused by late-ejected energetic material.

Abstract

Hyperluminous optical-ultraviolet fares have been detected in gamma-ray bursts and the luminosity record was held by naked-eye event GRB 080319B. Such fares 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 150s exposure of GRB 220101A, a burst at a redshift of 4.618, and report a rapidly evolving optical-ultraviolet fare with a high absolute AB magnitude of -39.4$\pm$0.2. In contrast to GRB 080319B, the temporal behaviour of this new fare does not trace the gamma-ray activity. Instead of either internal shocks or reverse shock, this extremely energetic optical-ultraviolet fare 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 fares and demonstrates the necessity of high-time-resolution observations at early times.