2021NatAs...5..262J

In the optical sky, minutes-duration transients from cosmological distances are rare. Known objects that give rise to such transients include gamma-ray bursts (GRBs), the most luminous explosions in the Universe1 that have been detected at redshifts as high as z ≃ 9.4 (refs. 2-4). These high-redshift GRBs and their associated emission can be used to probe the star formation and reionization history in the era of cosmic dawn. Here, we report a near-infrared transient with an observed duration shorter than 245 s that is coincident with the luminous star-forming galaxy GN-z11 at z ≃ 11. The telluric absorption shown in the near-infrared spectrum indicates that its origin is above the Earth's atmosphere. We can rule out the possibility of known man-made objects or moving objects in the Solar System on the basis of the observational information and our current understanding of the properties of these objects. As some long-duration GRBs are associated with a bright ultraviolet or optical flash5-14, we investigate the possibility that the detected signal arose from a rest-frame ultraviolet flash associated with a long GRB from GN-z11. Despite the very low probability of being a GRB, we find that the spectrum, brightness and duration of the transient are consistent with such an interpretation. Our result may suggest that long GRBs can be produced as early as 420 million years after the Big Bang.