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Survival Times of Supramassive Neutron Stars Resulting from Binary Neutron Star Mergers

Beniamini, Paz and Lu, Wenbin (2021) Survival Times of Supramassive Neutron Stars Resulting from Binary Neutron Star Mergers. Astrophysical Journal, 920 (2). Art. No. 109. ISSN 0004-637X. doi:10.3847/1538-4357/ac1678.

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A binary neutron star (BNS) merger can lead to various outcomes, from indefinitely stable neutron stars, through supramassive neutron stars (SMNSs) or hypermassive neutron stars supported only temporarily against gravity, to black holes formed promptly after the merger. Up-to-date constraints on the BNS total mass and the neutron star equation of state suggest that a long-lived SMNS may form in ∼0.45–0.9 of BNS mergers. A maximally rotating SMNS needs to lose ∼(3–6) × 10⁵² erg of its rotational energy before it collapses, on a fraction of the spin-down timescale. An SMNS formation imprints on the electromagnetic counterparts to the BNS merger. However, a comparison with observations reveals tensions. First, the distribution of collapse times is too wide and that of released energies too narrow (and the energy itself too large) to explain the observed distributions of internal X-ray plateaus, invoked as evidence for SMNS-powered energy injection. Second, the immense energy injection into the blast wave should lead to extremely bright radio transients, which previous studies found to be inconsistent with deep radio observations of short gamma-ray bursts (GRBs). Furthermore, we show that upcoming all-sky radio surveys will constrain the extracted energy distribution, independently of a GRB jet formation. Our results can be self-consistently understood, provided that most BNS merger remnants collapse shortly after formation (even if their masses are low enough to allow for SMNS formation). This naturally occurs if the remnant retains half or less of its initial energy by the time it enters solid-body rotation.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Beniamini, Paz0000-0001-7833-1043
Lu, Wenbin0000-0002-1568-7461
Additional Information:© 2021. The American Astronomical Society. Received 2021 June 4; revised 2021 July 16; accepted 2021 July 19; published 2021 October 20. We thank Pawan Kumar, Brian Metzger, and Kenta Hotokezaka for helpful discussions. P.B. was supported by the Gordon and Betty Moore Foundation, Grant GBMF5076. W.L. was supported by the David and Ellen Lee Fellowship at Caltech and Lyman Spitzer Jr. Fellowship at Princeton University.
Group:TAPIR, Walter Burke Institute for Theoretical Physics
Funding AgencyGrant Number
Gordon and Betty Moore FoundationGBMF5076
David and Ellen Lee Postdoctoral ScholarshipUNSPECIFIED
Princeton UniversityUNSPECIFIED
Subject Keywords:Gamma-ray bursts; Neutron stars; Gravitational waves
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Gamma-ray bursts (629); Neutron stars (1108); Gravitational waves (678)
Record Number:CaltechAUTHORS:20210408-121458570
Persistent URL:
Official Citation:Paz Beniamini and Wenbin Lu 2021 ApJ 920 109
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:108657
Deposited By: Tony Diaz
Deposited On:09 Apr 2021 17:54
Last Modified:02 Nov 2021 23:04

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