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Super-critical accretion onto a magnetized neutron star: modeling ULX pulsar
We performed general relativistic radiation MHD simulations of supercritical accretion flows onto magnetized neutron stars in order to understand the structure and observational properties of ultraluminous X-ray pulsars (ULXPs). The simulations consistently show the formation of supercritical accretion disks, radiation-driven optically thick outflows, and magnetically confined accretion flows near the neutron-star surface. We demonstrated that the observed soft thermal X-ray emission in Swift J0243.6+6124 can naturally originate from these outflows. We also investigated the effects of complex magnetic-field geometries, including dipole and quadrupole components, and showed that the magnetic topology strongly affects the inner accretion structure, producing either polar accretion columns or equatorial accretion belts. Our results suggest that Swift J0243.6+6124 may host a strong quadrupole magnetic field in addition to a weaker dipole component, highlighting the importance of multipolar magnetic fields in ULX pulsars.
Hyper-critical accretion onto a magnetied neutron star
We studied hypercritical fallback accretion onto magnetized proto–neutron stars using general relativistic MHD simulations including neutrino cooling. The goal was to understand under what conditions fallback material can bury the neutron-star magnetic field beneath a newly formed crust, as proposed for Central Compact Objects (CCOs). The simulations show that fallback accretion compresses the magnetosphere and forms a strong accretion shock, whose evolution is strongly affected by neutrino cooling. We derived a necessary condition for magnetic-field submergence by comparing the fallback timescale with the shock evolution timescale. This work provides a theoretical framework for understanding the diversity of young neutron stars, including magnetars, radio pulsars, and CCOs.We studied hypercritical fallback accretion onto magnetized proto–neutron stars using general relativistic MHD simulations including neutrino cooling. The goal was to understand under what conditions fallback material can bury the neutron-star magnetic field beneath a newly formed crust, as proposed for Central Compact Objects (CCOs). The simulations show that fallback accretion compresses the magnetosphere and forms a strong accretion shock, whose evolution is strongly affected by neutrino cooling. We derived a necessary condition for magnetic-field submergence by comparing the fallback timescale with the shock evolution timescale. This work provides a theoretical framework for understanding the diversity of young neutron stars, including magnetars, radio pulsars, and CCOs.
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