452 research outputs found
Modeling of Thermal Emission from ULX Pulsar Swift J0243.6+6124 with General Relativistic Radiation MHD simulations
We perform general relativistic radiation magnetohydrodynamics (MHD)
simulations of super-Eddington accretion flows around a neutron star with a
dipole magnetic field for modeling the galactic ultra-luminous X-ray source
(ULX) exhibiting X-ray pulsations, Swift J0243.6+6124. Our simulations show the
accretion columns near the magnetic poles, the accretion disk outside the
magnetosphere, and the outflows from the disk. It is revealed that the
effectively optically thick outflows, consistent with the observed thermal
emission at K, are generated if the mass accretion rate is much
higher than the Eddington rate and the magnetospheric
radius is smaller than the spherization radius. In order to explain the
blackbody radius ( km) without contradicting the reported spin
period () and spin-up rate (), the mass accretion rate of is
required. Since the thermal emission was detected in two observations with
of and but not in another with ,
the surface magnetic field strength of the neutron star in Swift J0243.6+6124
is estimated to be between and . From this restricted range of magnetic field strength, the accretion rate
would be when the thermal emission appears and
when it is not detected. Our results support the
hypothesis that the super-Eddington phase in the 2017-2018 giant outburst of
Swift J0243.6+6124 is powered by highly super-Eddington accretion flows onto a
magnetized neutron star.Comment: 24 pages, 9 figures, 2 tables, accepted for publication in Ap
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