Svinkin, D.D.SvinkinFrederiks, D.D.FrederiksHurley, K.K.HurleyAptekar, R.R.AptekarGolenetskii, S.S.GolenetskiiLysenko, A.A.LysenkoRidnaia, A. V.A. V.RidnaiaTsvetkova, A.A.TsvetkovaUlanov, M.M.UlanovCline, T. L.T. L.ClineMitrofanov, I.I.MitrofanovGolovin, D.D.GolovinKozyrev, A.A.KozyrevLitvak, M.M.LitvakSanin, A.A.SaninGoldstein, A.A.GoldsteinBriggs, M. S.M. S.BriggsWilson-Hodge, C.C.Wilson-Hodgevon Kienlin, A.A.von KienlinZhang, X. -L.X. -L.ZhangRau, A.A.RauSavchenko, V.V.SavchenkoBozzo, E.E.BozzoFerrigno, C.C.FerrignoUbertini, P.P.UbertiniBAZZANO, ANGELAANGELABAZZANORODI, James CraigJames CraigRODIBarthelmy, S.S.BarthelmyCummings, J.J.CummingsKrimm, H.H.KrimmPalmer, D. M.D. M.PalmerBoynton, W.W.BoyntonFellows, C. W.C. W.FellowsHarshman, K. P.K. P.HarshmanEnos, H.H.EnosStarr, R.R.Starr2025-03-172025-03-1720210028-0836http://hdl.handle.net/20.500.12386/36849Soft γ-ray repeaters exhibit bursting emission in hard X-rays and soft γ-rays. During the active phase, they emit random short (milliseconds to several seconds long), hard-X-ray bursts, with peak luminosities[1] of 10^36 to 10^43 erg per second. Occasionally, a giant flare with an energy of around 10^44 to 10^46 erg is emitted2. These phenomena are thought to arise from neutron stars with extremely high magnetic fields (10^14 to 10^15 gauss), called magnetars[1,3,4]. A portion of the second-long initial pulse of a giant flare in some respects mimics short γ-ray bursts[5,6], which have recently been identified as resulting from the merger of two neutron stars accompanied by gravitational-wave emission[7]. Two γ-ray bursts, GRB 051103 and GRB 070201, have been associated with giant flares[2,8,9,10,11]. Here we report observations of the γ-ray burst GRB 200415A, which we localized to a 20-square-arcmin region of the starburst galaxy NGC 253, located about 3.5 million parsecs away. The burst had a sharp, millisecond-scale hard spectrum in the initial pulse, which was followed by steady fading and softening over 0.2 seconds. The energy released (roughly 1.3 × 10^46 erg) is similar to that of the superflare[5,12,13] from the Galactic soft γ-ray repeater SGR 1806−20 (roughly 2.3 × 10^46 erg). We argue that GRB 200415A is a giant flare from a magnetar in NGC 253.STAMPAenArticle10.1038/s41586-020-03076-92-s2.0-85099401173https://www.nature.com/articles/s41586-020-03076-9https://api.elsevier.com/content/abstract/scopus_id/850994011732021Natur.589..211SFIS/05 - ASTRONOMIA E ASTROFISICA