GRB 210905A at z = 6.3: a powerful blast from the past

I shall be discussing the Gamma-ray Burst 210905A, an event both extremely powerful - with a energy release of ~ 10^54 erg - and extremely remote, being at redshift 6.3. The afterglow of this burst appears to be the most luminous of all Swift GRB afterglows at ~ 1 week after the trigger. This GRB grabs the attention also because its prompt emission might be unusually attributed to forward shock emission, while the afterglow appears to go through energy injection for almost one day. A jet break seems to be present as well, but it occurs late, indicating that high-z bursts may not have narrower jets that closer GRBs. I also discuss briefly the spectroscopic observations of this remote but extremely luminous "beacon"that have brought around a trove of data about the abundance of metals and their status in the host galaxy, when the Universe was less than one billion years old. Despite being very bright and distant, GRB 210905A seems just to be in the "high energy tail"of long GRBs, without properties that may let us think that its progenitor was unusual, for example a Population III star.