Extended Data Fig. 3: Prompt emission properties of GRB 230307A.

a,b, Gamma-ray lightcurves of GRB 230307A (red) and GRB 211211A (dark) from Fermi/GBM in the energy range of 10−25 keV and 0.8−10 MeV with 0.2 s binsize. The purple shaded area roughly represents the time range of the initial pulse of the lightcurve, as depicted in the zoomed-in panel (c) with 5 ms binsize in the energy range 10–350 keV. d, The Amati-relation diagram. The plum/gray/green circles represent Type I (short) GRBs/Type II (long) GRBs/magnetar giant flares, and the corresponding color solid line and the area between dashed lines are the best-fit model and 95% c.l., respectively. GRB 230307A (whole burst) shifts following the red line when located at different redshifts. The red stars represent it at the three most probable host galaxies (G1, LMC and G*), while the GF is only reasonable when we treat the initial pulse as the main burst (zoom-in panel c). Hybrid GRB 211211A is shown in the blue circle. The purple shaded (z > 0.23)/hatched (z > 0.43) area is ruled out by the expansion velocity of the photosphere radius at T₀ + 1.2 d/28.9 d being limited to less than the speed of light. The orange hatched area is ruled out by the SED (z ≲ 3.3). The red dashed line indicates the redshift where it departs from the 95% c.l. for the distribution of Type I GRBs. Error bars represent 1σ uncertainties.