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High-energy emission from a magnetar giant flare in the Sculptor galaxy

2021; Nature Portfolio; Volume: 5; Issue: 4 Linguagem: Inglês

10.1038/s41550-020-01287-8

2397-3366

M. Ajello, W. B. Atwood, M. Axelsson, L. Baldini, G. Barbiellini, Matthew G. Baring, D. Bastieri, R. Bellazzini, A. Berretta, E. Bissaldi, R. D. Blandford, R. Bonino, J. Bregeon, P. Bruel, R. Buehler, Eric Burns, S. Buson, R. A. Cameron, P. A. Caraveo, E. Cavazzuti, Shupei Chen, C. C. Cheung, G. Chiaro, S. Ciprini, D. Costantin, M. Crnogorčević, S. Cutini, F. D’Ammando, Pedro De la Torre Luque, F. de Palma, S. W. Digel, Niccolò Di Lalla, L. Di Venere, F. Dirirsa, Y. Fukazawa, S. Funk, P. Fusco, F. Gargano, N. Giglietto, Ramandeep Gill, F. Giordano, M. Giroletti, Jonathan Granot, D. Green, I. A. Grenier, S. Griffin, S. Guiriec, E. Hays, D. Horan, G. Jóhannesson, M. Kerr, M. Kovačević, M. Kuss, S. Larsson, L. Latronico, J. Li, F. Longo, F. Loparco, M. N. Lovellette, P. Lubrano, S. Maldera, Alberto Manfreda, G. Martí-Devesa, M. N. Mazziotta, J. E. McEnery, I. Mereu, P. F. Michelson, Tsunefumi Mizuno, M. E. Monzani, A. Morselli, I. V. Moskalenko, Michela Negro, N. Omodei, M. Orienti, E. Orlando, Vaidehi S. Paliya, D. Paneque, Z. Y. Pei, M. Pesce-Rollins, F. Piron, H. Poon, T. A. Porter, G. Principe, J. L. Racusin, S. Rainò, R. Rando, Bindu Rani, S. Razzaque, A. Reimer, O. Reimer, P. M. Saz Parkinson, J. D. Scargle, L. Scotton, D. Serini, C. Sgrò, E. J. Siskind, G. Spandre, P. Spinelli, H. Tajima, M. N. Takahashi, D. Tak, D. F. Torres, G. Tosti, E. Troja, Zorawar Wadiasingh, K. S. Wood, M. Yassine, Anke Yusafzai, G. Zaharijaš,

Pulsars and Gravitational Waves Research

Magnetars are the most highly magnetized neutron stars in the cosmos (with magnetic field 1013–1015 G). Giant flares from magnetars are rare, short-duration (about 0.1 s) bursts of hard X-rays and soft γ rays1,2. Owing to the limited sensitivity and energy coverage of previous telescopes, no magnetar giant flare has been detected at gigaelectronvolt (GeV) energies. Here, we report the discovery of GeV emission from a magnetar giant flare on 15 April 2020 (refs. 3,4 and A. J. Castro-Tirado et al., manuscript in preparation). The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope detected GeV γ rays from 19 s until 284 s after the initial detection of a signal in the megaelectronvolt (MeV) band. Our analysis shows that these γ rays are spatially associated with the nearby (3.5 megaparsecs) Sculptor galaxy and are unlikely to originate from a cosmological γ-ray burst. Thus, we infer that the γ rays originated with the magnetar giant flare in Sculptor. We suggest that the GeV signal is generated by an ultra-relativistic outflow that first radiates the prompt MeV-band photons, and then deposits its energy far from the stellar magnetosphere. After a propagation delay, the outflow interacts with environmental gas and produces shock waves that accelerate electrons to very high energies; these electrons then emit GeV γ rays as optically thin synchrotron radiation. This observation implies that a relativistic outflow is associated with the magnetar giant flare, and suggests the possibility that magnetars can power some short γ-ray bursts. Gigaelectronvolt emission from a magnetar giant flare is discovered by the Fermi Gamma-ray Space Telescope, between 19 s and 284 s after the initial detection of a signal in the megaelectronvolt energy band, potentially generated by an ultra-relativistic outflow far from the stellar magnetosphere.