JWST reveals a supernova following a gamma-ray burst at z ≃ 7.3

The majority of long-duration gamma-ray bursts (GRBs) are thought to arise from the collapse of massive stars, making them powerful tracers of star formation across cosmic time. Evidence for this origin comes from the presence of supernovae (SNe) in the aftermath of the GRB event, whose properties in turn link back to those of the collapsing star. In principle, thanks to GRBs, we can study the properties of individual stars in the distant Universe. Here, we present JWST/NIRCAM observations that have been able to detect both the host galaxy and a likely SN in the Space-based multi-band astronomical Variable Objects Monitor (SVOM) detected GRB 250314A. GRB 250314A has a spectroscopically measured redshift of z ≃ 7.3, placing it deep in the era of reionisation. The data are well described by a combination of faint blue host, similar to many z ∼ 7 galaxies, with a SN of similar luminosity to the prototype GRB SN, namely, SN 1998bw. The SN may be somewhat fainter if a larger contribution from the underlying galaxy is present, but SNe brighter than SN 1998bw can be excluded, given the evidence of low dust extinction, based on the blue afterglow colours. These observations suggest that despite disparate physical conditions, the star that created GRB 250314A was not much more massive and it might even resemble the GRB progenitors of the Local Universe.