The prompt optical/near-infrared flare of GRB 050904: The most luminous transient ever detected

With a redshift of z = 6.295, GRB 050904 is the most distant gamma-ray burst (GRB) ever discovered. It was an energetic event at all wavelengths, and the afterglow was observed in detail in the near-infrared (NIR) bands. We gathered all available optical and NIR afterglow photometry of this GRB to construct a composite NIR light curve spanning several decades in time and flux density. Transforming the NIR light curve into the optical, we find that the afterglow of GRB 050904 was more luminous at early times than any other GRB afterglow in the pre-Swift era, making it at these wavelengths the most luminous transient ever detected. Given the intrinsic properties of GRB 050904 and its afterglow, we discuss whether this burst is markedly different from other GRBs at lower redshifts.