Title

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

Authors

M. Ajello, Clemson University
W. B. Atwood, Santa Cruz Institute for Particle Physics
M. Axelsson, Stockholms universitet
L. Baldini, Istituto Nazionale di Fisica Nucleare, Sezione di Pisa
G. Barbiellini, Istituto Nazionale di Fisica Nucleare, Sezione di Trieste
M. G. Baring, Rice University
D. Bastieri, Istituto Nazionale Di Fisica Nucleare, Sezione di Padova
R. Bellazzini, Istituto Nazionale di Fisica Nucleare, Sezione di Pisa
A. Berretta, Università degli Studi di Perugia
E. Bissaldi, Politecnico di Bari
R. D. Blandford, SLAC National Accelerator Laboratory
R. Bonino, Istituto Nazionale di Fisica Nucleare, Sezione di Torino
J. Bregeon, Laboratoire Univers et Particules de Montpellier
P. Bruel, Laboratoire Leprince-Ringuet
R. Buehler, Deutsches Elektronen-Synchrotron (DESY)
E. Burns, Louisiana State University
S. Buson, Julius-Maximilians-Universität Würzburg
R. A. Cameron, SLAC National Accelerator Laboratory
P. A. Caraveo, INAF Istituto di Astrofisica Spaziale e Fisica Cosmica, Milan
E. Cavazzuti, Agenzia Spaziale Italiana
S. Chen, Istituto Nazionale Di Fisica Nucleare, Sezione di Padova
C. C. Cheung, Naval Research Laboratory
G. Chiaro, INAF Istituto di Astrofisica Spaziale e Fisica Cosmica, Milan
S. Ciprini, Istituto Nazionale di Fisica Nucleare - INFN
D. Costantin, Università degli Studi di Padova
M. Crnogorcevic, University of Maryland, College Park
S. Cutini, Istituto Nazionale di Fisica Nucleare, Sezione di Perugia
F. D’Ammando, Istituto Di Radioastronomia, Bologna
P. de la Torre Luque, Politecnico di Bari
F. de Palma, Istituto Nazionale di Fisica Nucleare, Sezione di Torino
S. W. Digel, SLAC National Accelerator Laboratory
N. Di Lalla, SLAC National Accelerator Laboratory
L. Di Venere, Politecnico di Bari

Document Type

Article

Publication Date

4-1-2021

Abstract

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.

Publication Source (Journal or Book title)

Nature Astronomy

First Page

385

Last Page

391

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