GR-RMHD Simulations of Super-Eddington Accretion Flows onto a Neutron Star with Dipole and Quadrupole Magnetic Fields
Although ultraluminous X-ray pulsars (ULXPs) are believed to be powered by super-Eddington accretion onto a magnetized neutron star (NS), the detailed structures of the inflow–outflow and magnetic fields are still not well understood. We perform general relativistic radiation magnetohydrodynamics (G...
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2024-01-01
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| Online Access: | https://doi.org/10.3847/1538-4357/ad8885 |
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| author | Akihiro Inoue Ken Ohsuga Hiroyuki R. Takahashi Yuta Asahina Matthew J. Middleton |
| author_facet | Akihiro Inoue Ken Ohsuga Hiroyuki R. Takahashi Yuta Asahina Matthew J. Middleton |
| author_sort | Akihiro Inoue |
| collection | DOAJ |
| description | Although ultraluminous X-ray pulsars (ULXPs) are believed to be powered by super-Eddington accretion onto a magnetized neutron star (NS), the detailed structures of the inflow–outflow and magnetic fields are still not well understood. We perform general relativistic radiation magnetohydrodynamics (GR-RMHD) simulations of super-Eddington accretion flows onto a magnetized NS with dipole and/or quadrupole magnetic fields. Our results show that an accretion disk and optically thick outflows form outside the magnetospheric radius, while inflows aligned with magnetic field lines appear inside. When the dipole field is more prominent than the quadrupole field at the magnetospheric radius, accretion columns form near the magnetic poles, whereas a quadrupole magnetic field stronger than the dipole field results in the formation of a belt-like accretion flow near the equatorial plane. The NS spins up as the angular momentum of the accreting gas is converted into the angular momentum of the electromagnetic field, which then flows into the NS. Even if an accretion column forms near one of the magnetic poles, the observed luminosity is almost the same on both the side with the accretion column and the side without it, because the radiation energy is transported to both sides through scattering. Our model suggests that galactic ULXP Swift J0243.6+6124 has a quadrupole magnetic field of 2 × 10 ^13 G and a dipole magnetic field of less than 4 × 10 ^12 G. |
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| language | English |
| publishDate | 2024-01-01 |
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| spelling | doaj-art-dbe10bf41d54437aa373db2f1476f9a92025-08-20T02:28:00ZengIOP PublishingThe Astrophysical Journal1538-43572024-01-0197711010.3847/1538-4357/ad8885GR-RMHD Simulations of Super-Eddington Accretion Flows onto a Neutron Star with Dipole and Quadrupole Magnetic FieldsAkihiro Inoue0https://orcid.org/0000-0002-0700-2223Ken Ohsuga1https://orcid.org/0000-0002-2309-3639Hiroyuki R. Takahashi2https://orcid.org/0000-0003-0114-5378Yuta Asahina3https://orcid.org/0000-0003-3640-1749Matthew J. Middleton4https://orcid.org/0000-0002-8183-2970Department of Earth and Space Science, Graduate School of Science, Osaka University , Toyonaka, Osaka 560-0043, Japan ; ainoue@astro-osaka.jpCenter for Computational Sciences, University of Tsukuba , 1-1-1 Ten-nodai, Tsukuba, Ibaraki 305-8577, JapanDepartment of Natural Sciences, Faculty of Arts and Sciences, Komazawa University , Tokyo 154-8525, JapanCenter for Computational Sciences, University of Tsukuba , 1-1-1 Ten-nodai, Tsukuba, Ibaraki 305-8577, JapanSchool of Physics & Astronomy, University of Southampton , Southampton, Southampton SO17 1BJ, UKAlthough ultraluminous X-ray pulsars (ULXPs) are believed to be powered by super-Eddington accretion onto a magnetized neutron star (NS), the detailed structures of the inflow–outflow and magnetic fields are still not well understood. We perform general relativistic radiation magnetohydrodynamics (GR-RMHD) simulations of super-Eddington accretion flows onto a magnetized NS with dipole and/or quadrupole magnetic fields. Our results show that an accretion disk and optically thick outflows form outside the magnetospheric radius, while inflows aligned with magnetic field lines appear inside. When the dipole field is more prominent than the quadrupole field at the magnetospheric radius, accretion columns form near the magnetic poles, whereas a quadrupole magnetic field stronger than the dipole field results in the formation of a belt-like accretion flow near the equatorial plane. The NS spins up as the angular momentum of the accreting gas is converted into the angular momentum of the electromagnetic field, which then flows into the NS. Even if an accretion column forms near one of the magnetic poles, the observed luminosity is almost the same on both the side with the accretion column and the side without it, because the radiation energy is transported to both sides through scattering. Our model suggests that galactic ULXP Swift J0243.6+6124 has a quadrupole magnetic field of 2 × 10 ^13 G and a dipole magnetic field of less than 4 × 10 ^12 G.https://doi.org/10.3847/1538-4357/ad8885Radiative magnetohydrodynamicsHigh energy astrophysicsUltraluminous x-ray sourcesGeneral relativityAccretionNeutron stars |
| spellingShingle | Akihiro Inoue Ken Ohsuga Hiroyuki R. Takahashi Yuta Asahina Matthew J. Middleton GR-RMHD Simulations of Super-Eddington Accretion Flows onto a Neutron Star with Dipole and Quadrupole Magnetic Fields The Astrophysical Journal Radiative magnetohydrodynamics High energy astrophysics Ultraluminous x-ray sources General relativity Accretion Neutron stars |
| title | GR-RMHD Simulations of Super-Eddington Accretion Flows onto a Neutron Star with Dipole and Quadrupole Magnetic Fields |
| title_full | GR-RMHD Simulations of Super-Eddington Accretion Flows onto a Neutron Star with Dipole and Quadrupole Magnetic Fields |
| title_fullStr | GR-RMHD Simulations of Super-Eddington Accretion Flows onto a Neutron Star with Dipole and Quadrupole Magnetic Fields |
| title_full_unstemmed | GR-RMHD Simulations of Super-Eddington Accretion Flows onto a Neutron Star with Dipole and Quadrupole Magnetic Fields |
| title_short | GR-RMHD Simulations of Super-Eddington Accretion Flows onto a Neutron Star with Dipole and Quadrupole Magnetic Fields |
| title_sort | gr rmhd simulations of super eddington accretion flows onto a neutron star with dipole and quadrupole magnetic fields |
| topic | Radiative magnetohydrodynamics High energy astrophysics Ultraluminous x-ray sources General relativity Accretion Neutron stars |
| url | https://doi.org/10.3847/1538-4357/ad8885 |
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