MEREGHETTI, SandroSandroMEREGHETTIRIGOSELLI, MichelaMichelaRIGOSELLISALVATERRA, RubenRubenSALVATERRAPacholski, Dominik PatrykDominik PatrykPacholskiRODI, James CraigJames CraigRODIGotz, DiegoDiegoGotzARRIGONI, EdoardoEdoardoARRIGONID'AVANZO, PaoloPaoloD'AVANZOAdami, ChristopheChristopheAdamiBAZZANO, ANGELAANGELABAZZANOBOZZO , ENRICOENRICOBOZZOBRIVIO, RiccardoRiccardoBRIVIOCAMPANA, SergioSergioCAMPANACAPPELLARO, EnricoEnricoCAPPELLAROChenevez, JeromeJeromeChenevezDE LUISE, FioreFioreDE LUISEDucci, LorenzoLorenzoDucciESPOSITO, PAOLOPAOLOESPOSITOFerrigno, CarloCarloFerrignoFERRO, MatteoMatteoFERROISRAEL, Gian LucaGian LucaISRAELLe Floc'h, EmericEmericLe Floc'hMartin-Carrillo, AntonioAntonioMartin-CarrilloONORI, FrancescaFrancescaONORIRea, NandaNandaReaREGUITTI, AndreaAndreaREGUITTISavchenko, VolodymyrVolodymyrSavchenkoSouami, DamyaDamyaSouamiTARTAGLIA, LeonardoLeonardoTARTAGLIAThuillot, WilliamWilliamThuillotTIENGO, ANDREAANDREATIENGOTOMASELLA, LinaLinaTOMASELLATOPINKA, MartinMartinTOPINKATurpin, DamienDamienTurpinUBERTINI, PIETROPIETROUBERTINI2025-02-132025-02-1320240028-0836http://hdl.handle.net/20.500.12386/35937Magnetar giant flares are rare explosive events releasing up to 10<SUP>47</SUP> erg in gamma rays in less than 1 second from young neutron stars with magnetic fields up to 10<SUP>15−16</SUP> G (refs. <SUP>1,2</SUP>). Only three such flares have been seen from magnetars in our Galaxy<SUP>3,4</SUP> and in the Large Magellanic Cloud<SUP>5</SUP> in roughly 50 years. This small sample can be enlarged by the discovery of extragalactic events, as for a fraction of a second giant flares reach luminosities above 10<SUP>46</SUP> erg s<SUP>−1</SUP>, which makes them visible up to a few tens of megaparsecs. However, at these distances they are difficult to distinguish from short gamma-ray bursts (GRBs); much more distant and energetic (10<SUP>50−53</SUP> erg) events, originating in compact binary mergers<SUP>6</SUP>. A few short GRBs have been proposed<SUP>7-11</SUP>, with different amounts of confidence, as candidate giant magnetar flares in nearby galaxies. Here we report observations of GRB 231115A, positionally coincident with the starburst galaxy M82 (ref. <SUP>12</SUP>). Its spectral properties, along with the length of the burst, the limits on its X-ray and optical counterparts obtained within a few hours, and the lack of a gravitational wave signal, unambiguously qualify this burst as a giant flare from a magnetar in M82.STAMPAenArticle10.1038/s41586-024-07285-42-s2.0-85191339415https://api.elsevier.com/content/abstract/scopus_id/85191339415https://www.nature.com/articles/s41586-024-07285-42024Natur.629...58MFIS/05 - ASTRONOMIA E ASTROFISICA