ISRAEL, Gian LucaGian LucaISRAEL0000-0001-5480-6438Belfiore, AndreaAndreaBelfioreSTELLA, LuigiLuigiSTELLA0000-0002-0018-1687ESPOSITO, PAOLOPAOLOESPOSITO0000-0003-4849-5092CASELLA, PiergiorgioPiergiorgioCASELLA0000-0002-0752-3301DE LUCA, AndreaAndreaDE LUCA0000-0001-6739-687XMARELLI, MARTINOMARTINOMARELLI0000-0002-8017-0338PAPITTO, ALESSANDROALESSANDROPAPITTO0000-0001-6289-7413PERRI, MatteoMatteoPERRI0000-0003-3613-4409Puccetti, SimonettaSimonettaPuccettiRODRIGUEZ CASTILLO, Guillermo AndresGuillermo AndresRODRIGUEZ CASTILLO0000-0003-3952-7291Salvetti, DavidDavidSalvettiTIENGO, ANDREAANDREATIENGO0000-0002-6038-1090ZAMPIERI, LucaLucaZAMPIERI0000-0002-6516-1329D'Agostino, DanieleDanieleD'AgostinoGreiner, JochenJochenGreinerHaberl, FrankFrankHaberlNovara, GiovanniGiovanniNovaraSALVATERRA, RubenRubenSALVATERRA0000-0002-9393-8078Turolla, RobertoRobertoTurollaWatson, MikeMikeWatsonWilms, JoernJoernWilmsWOLTER, Anna Luisa MariaAnna Luisa MariaWOLTER0000-0001-5840-98352020-12-142020-12-1420170036-8075http://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