Spectral Analysis of GRB 220426A: Another Case of a Thermally Dominated Burst

We report a very bright, long-duration gamma-ray burst (GRB), GRB 220426A, observed by the Fermi satellite. GRB 220426A, with a total duration of T90 = 6 s, is composed of two main pulses and some subpeaks. The spectral analysis of this burst with a Band function reveals that both the time-integrated and the time-resolved spectra are very narrow with a high α ≳ 0.2 and low β ≲ −3.1. It is highly reminiscent of GRB 090902B, a special GRB with a photospheric emission identification. Then, we perform the spectral analysis of this burst based on nondissipated photospheric emission, which can be well modeled by a multicolor blackbody with a cutoff power-law distribution of the thermal temperature. The spectral fittings reveal that the photospheric emission can well describe the radiation spectrum of this burst. We conclude that this burst would be a second burst in the class of GRB 090902B observed by the Fermi satellite. We also discuss the physics of the photosphere and the origin of the high-energy component in GRB 220426A.