Fig. 1: The high-energy properties of GRB 230307A.
From: Heavy-element production in a compact object merger observed by JWST
a, The light curve of the GRB at 64-ms time resolution with the Fermi/GBM. The shaded region indicates the region in which saturation may be an issue. The burst begins very hard, with the count rate dominated by photons in the hardest (100–900-keV) band, but rapidly softens, with the count rate in the hard band being progressively overtaken by softer bands (such as 8–25 keV and 25–100 keV) beyond about 20 s. This strong hard-to-soft evolution is reminiscent of GRB 211211A (ref. 20) and is caused by the motion of two spectral breaks through the gamma-ray regime (see Methods). b, The X-ray light curves of GRBs from the Swift X-ray telescope. These have been divided by the prompt fluence of the burst, which broadly scales with the X-ray light curve luminosity, resulting in a modest spread of afterglows. The greyscale background represents the ensemble of long GRBs. GRB 230307A is an extreme outlier of the >1,000 Swift GRBs, with an extremely faint afterglow for the brightness of its prompt emission. Other merger GRBs from long bursts, and those suggested to be short with extended emission (EE), occupy a similar region of the parameter space. This suggests that the prompt to afterglow fluence could be a valuable tool in distinguishing long GRBs from mergers and those from supernovae.
