ISRAEL, Gian LucaGian LucaISRAELBelfiore, AndreaAndreaBelfioreSTELLA, LuigiLuigiSTELLAESPOSITO, PAOLOPAOLOESPOSITOCASELLA, PiergiorgioPiergiorgioCASELLADE LUCA, AndreaAndreaDE LUCAMARELLI, MARTINOMARTINOMARELLIPAPITTO, ALESSANDROALESSANDROPAPITTOPERRI, MatteoMatteoPERRIPuccetti, SimonettaSimonettaPuccettiRODRIGUEZ CASTILLO, Guillermo AndresGuillermo AndresRODRIGUEZ CASTILLOSalvetti, DavidDavidSalvettiTIENGO, ANDREAANDREATIENGOZAMPIERI, LucaLucaZAMPIERID'Agostino, DanieleDanieleD'AgostinoGreiner, JochenJochenGreinerHaberl, FrankFrankHaberlNovara, GiovanniGiovanniNovaraSALVATERRA, RubenRubenSALVATERRATurolla, RobertoRobertoTurollaWatson, MikeMikeWatsonWilms, JoernJoernWilmsWOLTER, Anna Luisa MariaAnna Luisa MariaWOLTER2020-12-142020-12-1420170036-8075http://hdl.handle.net/20.500.12386/28829Ultraluminous x-ray sources (ULXs) in nearby galaxies shine brighter than any x-ray source in our Galaxy. ULXs are usually modeled as stellar-mass black holes (BHs) accreting at very high rates or intermediate-mass BHs. We present observations showing that NGC 5907 ULX is instead an x-ray accreting neutron star (NS) with a spin period evolving from 1.43 seconds in 2003 to 1.13 seconds in 2014. It has an isotropic peak luminosity of ~1000 times the Eddington limit for a NS at 17.1 megaparsec. Standard accretion models fail to explain its luminosity, even assuming beamed emission, but a strong multipolar magnetic field can describe its properties. These findings suggest that other extreme ULXs (x-ray luminosity ≥ 10<SUP>41</SUP> erg second<SUP>-1</SUP>) might harbor NSs.STAMPAenArticle10.1126/science.aai86352-s2.0-85013993738000395127600036https://science.sciencemag.org/content/355/6327/8172017Sci...355..817IFIS/05 - ASTRONOMIA E ASTROFISICA