PoS - Proceedings of Science
Volume 444 - 38th International Cosmic Ray Conference (ICRC2023) - Gamma-ray Astronomy (GA)
Detection of GeV emission from an ultralong gamma-ray burst with the Fermi Large Area Telescope
Y. Huang*, H.M. Zhang, K. Yan, R.Y. Liu and X.Y. Wang
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Pre-published on: August 14, 2023
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GRB 220627A, detected by Fermi Gamma-ray Burst Monitor (GBM), is a potential gravitationally lensed gamma-ray burst (GRB), because it has two similar episodes in terms of temporal shapes and spectra. However, by analyzing data from the Fermi Large Area Telescope, we found significant differences in gamma-ray photon numbers between the two episodes. This evidence, combined with a comprehensive spectral study, strongly suggests that GRB 220627A isn't a lensed burst. Instead, it is identified as an ultralong gamma-ray burst, one with emissions lasting over 1000 seconds. Notably, this is the first observation of GeV emissions from such a long burst. Additionally, the detection of a 15.7 GeV photon during the early prompt phase places a lower limit of $\Gamma\ge300$ on the bulk Lorentz factor of the GRB ejecta. The constraint on the bulk Lorentz factor could shed light on the origin of ultralong GRBs.
DOI: https://doi.org/10.22323/1.444.0828
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