GRB 221009A, its precursor and two afterglows in the Fermi data

Abstract

We study GRB 221009A, the brightest gamma-ray burst in the history of observations, using Fermi data. To calibrate them for large inclination angles, we use the Vela X gamma-ray source. Light curves in different spectral ranges demonstrate a 300 s overlap of afterglow and delayed episodes of soft prompt emission. We demonstrate that a relatively weak burst precursor that occurs 3 minutes before the main episode has its own afterglow, i.e., presumably, its own external shock. The main afterglow is the brightest one, includes a photon with an energy of 400 GeV 9 hours after the burst, and is visible in the LAT data for up to two days.