Flares, Jets, and Quasiperiodic Outbursts from Neutron Star Merger Remnants

Abstract

Using numerical relativity simulations with a subgrid dynamo prescription to generate strong initial magnetic fields, we investigate the possibility of launching a jet-like outflow from the hypermassive neutron star (HMNS) during the early stages of the merger, prior to the remnant's collapse to a black hole. We demonstrate that buoyant instabilities in the strongly magnetized HMNS can lead to a periodic emission of powerful electromagnetic flares shortly after the merger. These are followed by a collimated mildly relativistic outflow. Both types of outflows feature quasiperiodic kilohertz substructure. These early-time outflows may power precursors to short-duration gamma-ray bursts (sGRBs) or in some cases the entire sGRB. While the overall temporal power spectrum we find broadly agrees with the one recently reported for quasiperiodic oscillations in the sGRB GRB910711, our simulations suggest that the periodic electromagnetic substructure is dominated by magnetohydrodynamic shearing processes rather than correlating with the corresponding postmerger gravitational-wave signal.

Additional Information

© 2023. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. E.R.M. thanks A. Beloborodov, K. Chatziioannou, A. Philippov, and C. Raithel for insightful discussions related to this work. E.R.M. gratefully acknowledges support as the John Archibald Wheeler Fellow at Princeton University (PCTS), and from the Institute for Advanced Study. The simulations were performed on Delta at the National Center for Supercomputing Applications (NCSA) through allocation PHY210074 from the Advanced Cyberinfrastructure Coordination Ecosystem: Services & Support (ACCESS) program, which is supported by National Science Foundation grants #2138259, #2138286, #2138307, #2137603, and #2138296. Part of the simulations were carried out on NSF Frontera supercomputer under grant AST21006. E.Q. was supported in part by a Simons Investigator award from the Simons Foundation. Software: EinsteinToolkit (Loffler et al. 2012), kuibit (Bozzola 2021), matplotlib (Hunter 2007), numpy (Harris et al. 2020), scipy (Virtanen et al. 2020).

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