Black hole pulsars and monster shocks as outcomes of black hole--neutron star mergers
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| Format: | Preprint |
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2024
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| _version_ | 1866913771275943936 |
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| author | Kim, Yoonsoo Most, Elias R. Beloborodov, Andrei M. Ripperda, Bart |
| author_facet | Kim, Yoonsoo Most, Elias R. Beloborodov, Andrei M. Ripperda, Bart |
| contents | The merger of a black hole (BH) and a neutron star (NS) in most cases is expected to leave no material around the remnant BH; therefore, such events are often considered as sources of gravitational waves without electromagnetic counterparts. However, a bright counterpart can emerge if the NS is strongly magnetized, as its external magnetosphere can experience radiative shocks and magnetic reconnection during/after the merger. We use magnetohydrodynamic simulations in the dynamical spacetime of a merging BH--NS binary to investigate its magnetospheric dynamics. We find that compressive waves excited in the magnetosphere develop into monster shocks as they propagate outward. After swallowing the NS, the BH acquires a magnetosphere that quickly evolves into a split monopole configuration and then undergoes an exponential decay (balding), enabled by magnetic reconnection and also assisted by the ring-down of the remnant BH. This spinning BH drags the split monopole into rotation, forming a transient pulsar-like state. It emits a striped wind if the swallowed magnetic dipole moment is inclined to the spin axis. We predict two types of transients from this scenario: (1) a fast radio burst emitted by the shocks as they expand to large radii and (2) an X/$γ$-ray burst emitted by the $e^\pm$ outflow heated by magnetic dissipation. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2412_05760 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Black hole pulsars and monster shocks as outcomes of black hole--neutron star mergers Kim, Yoonsoo Most, Elias R. Beloborodov, Andrei M. Ripperda, Bart High Energy Astrophysical Phenomena General Relativity and Quantum Cosmology The merger of a black hole (BH) and a neutron star (NS) in most cases is expected to leave no material around the remnant BH; therefore, such events are often considered as sources of gravitational waves without electromagnetic counterparts. However, a bright counterpart can emerge if the NS is strongly magnetized, as its external magnetosphere can experience radiative shocks and magnetic reconnection during/after the merger. We use magnetohydrodynamic simulations in the dynamical spacetime of a merging BH--NS binary to investigate its magnetospheric dynamics. We find that compressive waves excited in the magnetosphere develop into monster shocks as they propagate outward. After swallowing the NS, the BH acquires a magnetosphere that quickly evolves into a split monopole configuration and then undergoes an exponential decay (balding), enabled by magnetic reconnection and also assisted by the ring-down of the remnant BH. This spinning BH drags the split monopole into rotation, forming a transient pulsar-like state. It emits a striped wind if the swallowed magnetic dipole moment is inclined to the spin axis. We predict two types of transients from this scenario: (1) a fast radio burst emitted by the shocks as they expand to large radii and (2) an X/$γ$-ray burst emitted by the $e^\pm$ outflow heated by magnetic dissipation. |
| title | Black hole pulsars and monster shocks as outcomes of black hole--neutron star mergers |
| topic | High Energy Astrophysical Phenomena General Relativity and Quantum Cosmology |
| url | https://arxiv.org/abs/2412.05760 |