@Article{LimaCoePerRodRue:2020:EvMuMa,
               author = "Lima, Rafael Camargo Rodrigues de and Coelho, Jaziel Goulart and 
                         Pereira, Jonas Pedro and Rodrigues, Cl{\'a}udia Vilega and Rueda, 
                         Jorge A.",
          affiliation = "{Universidade do Estado de Santa Catarina (UDESC)} and ICRANet and 
                         {Universidade Federal do ABC (UFABC)} and {Instituto Nacional de 
                         Pesquisas Espaciais (INPE)} and ICRANet",
                title = "Evidence for a multipolar magnetic field in SGR J1745-2900 from 
                         X-ray light-curve analysis",
              journal = "Astrophysical Journal",
                 year = "2020",
               volume = "889",
               number = "2",
                pages = "e165",
                month = "fev.",
             keywords = "dense matter – pulsars: general – stars: neutron – starspots – 
                         X-rays: individual.",
             abstract = "SGR J1745-2900 was detected from its outburst activity in 2013 
                         April and it was the first soft gamma repeater (SGR) detected near 
                         the center of the Galaxy (Sagittarius A* ). We use 3.5 yr Chandra 
                         X-ray light-curve data to constrain some neutron star (NS) 
                         geometric parameters. We assume that the flux modulation comes 
                         from hot spots on the stellar surface. Our model includes the NS 
                         mass, radius, a maximum of three spots of any size, temperature 
                         and positions, and general relativistic effects. We find that the 
                         light curve of SGR J1745-2900 could be described by either two or 
                         three hot spots. The ambiguity is due to the small amount of data, 
                         but our analysis suggests that one should not disregard the 
                         possibility of multi-spots (due to a multipolar magnetic field) in 
                         highly magnetized stars. For the case of three hot spots, we find 
                         that they should be large and have angular semiapertures ranging 
                         from 16° to 67°. The large size found for the spots points to a 
                         magnetic field with a nontrivial poloidal and toroidal structure 
                         (in accordance with magnetohydrodynamics investigations and 
                         Neutron Star Interior Composition Explorers (NICER) recent 
                         findings for PSR J0030+0451) and is consistent with the small 
                         characteristic age of the star. Finally, we also discuss possible 
                         constraints on the mass and radius of SGR J1745-2900 and briefly 
                         envisage possible scenarios accounting for the 3.5 yr evolution of 
                         SGR J1745-290 hot spots.",
                  doi = "10.3847/1538-4357/ab65f4",
                  url = "http://dx.doi.org/10.3847/1538-4357/ab65f4",
                 issn = "0004-637X and 1538-4357",
             language = "en",
           targetfile = "lima_evidence.pdf",
        urlaccessdate = "27 abr. 2024"
}