A long gamma-ray burst (GRB) is observed when the collapse of a massive star produces an ultrarelativistic outflow pointed toward Earth. Gamma-ray spectra of long GRBs are smooth, typically modeled by joint power-law segments describing a continuum, with no detected spectral lines. We report a significant (>6σ) narrow emission feature at ~10 mega-electron volts (MeV) in the spectrum of the bright GRB 221009A. Over 80 seconds, it evolves in energy (~12 to ~6 MeV) and in luminosity (~1.1 to <0.43 × 1050 erg second-1) but has a constant width of ~1 MeV. We interpret this feature as a blueshifted spectral line produced by the annihilation of electron-positron pairs, potentially in the same location responsible for emitting the brightest GRB pulses.
A mega–electron volt emission line in the spectrum of a gamma-ray burst / Ravasio, Maria Edvige; Salafia, Om Sharan; Oganesyan, Gor; Mei, Alessio; Ghirlanda, Giancarlo; Ascenzi, Stefano; Banerjee, Biswajit; Macera, Samanta; Branchesi, Marica; Jonker, Peter G.; Levan, Andrew J.; Malesani, Daniele B.; Mulrey, Katharine B.; Giuliani, Andrea; Celotti, Annalisa; Ghisellini, Gabriele. - In: SCIENCE. - ISSN 0036-8075. - 385:6707(2024), pp. 452-455. [10.1126/science.adj3638]
A mega–electron volt emission line in the spectrum of a gamma-ray burst
Celotti, Annalisa;
2024-01-01
Abstract
A long gamma-ray burst (GRB) is observed when the collapse of a massive star produces an ultrarelativistic outflow pointed toward Earth. Gamma-ray spectra of long GRBs are smooth, typically modeled by joint power-law segments describing a continuum, with no detected spectral lines. We report a significant (>6σ) narrow emission feature at ~10 mega-electron volts (MeV) in the spectrum of the bright GRB 221009A. Over 80 seconds, it evolves in energy (~12 to ~6 MeV) and in luminosity (~1.1 to <0.43 × 1050 erg second-1) but has a constant width of ~1 MeV. We interpret this feature as a blueshifted spectral line produced by the annihilation of electron-positron pairs, potentially in the same location responsible for emitting the brightest GRB pulses.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
