Speaker
Description
Starting from the unequivocal detection of very high energy (VHE) emission by Imaging Atmospheric Cherenkov Telescopes (IACTs) from the luminous gamma-ray burst (GRB) GRB 190114C and GRB 180720B, VHE observations of GRBs have become a new probe to explore the GRB physics. On October 9th, 2022, the exceptionally bright gamma-ray burst, GRB 221009A, was initially detected by the Fermi-GBM and Swift/BAT and subsequently by other satellites and ground-based telescopes across all different wavelengths. Due to its large isotropic equivalent energy release (2 × 10^54 erg) and relatively low redshift z = 0.151, this event is the brightest GRB ever recorded. Moreover, ground-based particle detector array experiment LHAASO reported the detection of gamma rays whose energies are exceeding 10 TeV.
The first Large-Sized Telescope (LST-1) of the next-generation ground-based gamma-ray observatory Cherenkov Telescope Array Observatory (CTAO) was inaugurated in 2018 and it is now establishing the early-science phase. Despite of the strong moonlight in the first few days, LST-1 performed follow-up observations of GRB 221009A 1.33 days after the burst onset and continued for more than 20 days, which makes this follow-up the promptest observations on this source by IACTs and the largest GRB campaign by LST-1 so far. The strong moon conditions in the first days required a dedicated procedure to obtain the best telescope performance under such extreme background. The dedicated analysis of the first night resulted in a hint of a signal. In this contribution, we will report the analysis results and a possible physical interpretation of the LST-1 observations of GRB 221009A.
