GRB 221009A: Observations with LST-1 of CTAO and Implications for Structured Jets in Long Gamma-Ray Bursts

Abstract

GRB 221009A is the brightest gamma-ray burst (GRB) observed to date. Extensive observations of its afterglow emission across the electromagnetic spectrum were performed, providing the first strong evidence of a jet with a nontrivial angular structure in a long GRB. We carried out an extensive observation campaign in very-high-energy (VHE) gamma rays with the first Large-Sized Telescope of the future Cherenkov Telescope Array Observatory, starting on 2022 October 10, about 1 day after the burst. A dedicated analysis of the GRB 221009A data is performed to account for the different moonlight conditions under which data were recorded. We find an excess of gamma-like events with a statistical significance of 4.1$\sigma$ during the observations taken 1.33 days after the burst, followed by background-compatible results for the later days. The results are compared with various models of afterglows from structured jets that are consistent with the published multiwavelength data but entail significant quantitative and qualitative differences in the VHE emission after 1 day. We disfavor models that imply VHE flux at 1 day considerably above $10^{-11}$ erg cm${}^{-2}$ s${}^{-1}$. Our late-time VHE observations can help disentangle the degeneracy among the models and provide valuable new insight into the structure of GRB jets.

20 pages, 7 figures. Published in The Astrophysical Journal Letters

References in corpus (31)

• The Supernova -- Gamma-Ray Burst Connection
• The Physics of Gamma-Ray Bursts and Relativistic Jets
• Teraelectronvolt emission from the $\gamma$-ray burst GRB 190114C
• A very-high-energy component deep in the Gamma-ray Burst afterglow
• A tera-electronvolt afterglow from a narrow jet in an extremely bright gamma-ray burst 221009A
• Revealing x-ray and gamma ray temporal and spectral similarities in the GRB 190829A afterglow
• Fermi-GBM Discovery of GRB 221009A: An Extraordinarily Bright GRB from Onset to Afterglow
• Gamma Ray Bursts
• Very high energy gamma-ray emission beyond 10 TeV from GRB 221009A
• GRB 221009A: Discovery of an Exceptionally Rare Nearby and Energetic Gamma-Ray Burst
• Gammapy: A Python package for gamma-ray astronomy
• The Radio to GeV Afterglow of GRB 221009A
• High energy gamma-ray emission from Gamma-Ray Bursts -- before GLAST
• Monte Carlo studies for the optimisation of the Cherenkov Telescope Array layout
• MAGIC observations of the nearby short gamma-ray burst GRB 160821B
• GRB 221009A Afterglow from a Shallow Angular Structured Jet
• Two-component jet model for multiwavelength afterglow emission of the extremely energetic burst GRB 221009A
• Gamma-ray bursts afterglow physics and the VHE domain
• Observations of the Crab Nebula and Pulsar with the Large-Sized Telescope Prototype of the Cherenkov Telescope Array
• H.E.S.S. follow-up observations of GRB221009A
• AGILE gamma-ray detection of the exceptional GRB 221009A
• Gamma-ray Observations Under Bright Moonlight with VERITAS
• MAGIC detection of GRB 201216C at $z=1.1$
• A Narrow Uniform Core with a Wide Structured Wing: Modeling the TeV and Multi-wavelength Afterglows of GRB 221009A
• Synchrotron Self-Compton Emission in the Two-Component Jet Model for Gamma-Ray Bursts
• The origin of very-high-energy gamma-rays from GRB 221009A: implications for reverse shock proton synchrotron emission
• Detection of RS Oph with LST-1 and modelling of its HE/VHE gamma-ray emission
• Current status and operation of the H.E.S.S. array of imaging atmospheric Cherenkov telescopes
• Theoretical modeling of the exceptional GRB 221009A afterglow
• The expansion of the GRB 221009A afterglow
• LST-1 observations of an enormous flare of BL Lacertae in 2021

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