Fermi Observations of GRB 220426A: a burst similar to GRB 090902B

TL;DR

This paper reports on the Fermi observations of a bright, long-duration gamma-ray burst, GRB 220426A, which exhibits spectral features similar to the well-studied GRB 090902B, suggesting a photospheric emission origin.

Contribution

The study identifies GRB 220426A as a second example of a burst with photospheric emission similar to GRB 090902B, using detailed spectral analysis with a multicolor-blackbody model.

Findings

Spectral analysis shows narrow spectra with high alpha and low beta.

Photospheric emission models fit the burst's spectrum well.

GRB 220426A is likely a second example of photospheric emission in GRBs.

Abstract

We report on a very bright, long-duration gamma-ray burst (GRB), GRB~220426A, observed by \emph{Fermi} satellite. GRB~220426A with total duration of $T_{90}=6$~s is composed with two main pulses and some sub-peaks. The spectral analysis of this burst with Band function reveals that both the time-integrated and the time-resolved spectra are very narrow with high $\alpha \gtrsim 0.2$ and low $\beta\lesssim -3.1$. It is strong reminiscent of GRB~090902B, a special GRB with identification of the photospheric emission. Then, we perform the spectral analysis of this burst based on a non-dissipated photospheric emission, which can be well modelled as the 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 \emph{Fermi} satellite. We also discuss the physics of photosphere and the origin of the high-energy component in GRB~220426A .