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Magnetic Interactions in Coalescing Neutron Star Binaries

Piro, Anthony L. (2012) Magnetic Interactions in Coalescing Neutron Star Binaries. Astrophysical Journal, 755 (1). Art. No. 80. ISSN 0004-637X.

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It is expected on both evolutionary and empirical grounds that many merging neutron star (NS) binaries are composed of a highly magnetized NS in orbit with a relatively low magnetic field NS. I study the magnetic interactions of these binaries using the framework of a unipolar inductor model. The electromotive force generated across the non-magnetic NS as it moves through the magnetosphere sets up a circuit connecting the two stars. The exact features of this circuit depend on the uncertain resistance in the space between the stars R_(space). Nevertheless, I show that there are interesting observational and/or dynamical effects irrespective of its exact value. When R_(space) is large, electric dissipation as great as ~10^(46) erg s^(–1) (for magnetar-strength fields) occurs in the magnetosphere, which would exhibit itself as a hard X-ray precursor in the seconds leading up to merger. With less certainty, there may also be an associated radio transient. When R_(space) is small, electric dissipation largely occurs in the surface layers of the magnetic NS. This can reach ~10^(49) erg s^(–1) during the final ~1 s before merger, similar to the energetics and timescales of short gamma-ray bursts. In addition, for dipole fields greater than ≈10^(12) G and a small R_(space), magnetic torques spin up the magnetized NS. This drains angular momentum from the binary and accelerates the inspiral. A faster coalescence results in less orbits occurring before merger, which would impact matched-filtering gravitational-wave searches by ground-based laser interferometers and could create difficulties for studying alternative theories of gravity with compact inspirals.

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Additional Information:© 2012 American Astronomical Society. Received 2012 May 26, accepted for publication 2012 June 21. Published 2012 July 27. I thank Douglas N. C. Lin for discussions of the unipolar inductor model (in a different context), which provided the impetus for this research. I thank the referee for insightful questions that helped better develop some of the discussions in this paper. I also thank Andrei Beloborodov, Lars Bildsten, Philip Chang, Peter Goldreich, Maxim Lyutikov, Christian Ott, Anatoly Spitkovsky, and David Tsang for helpful comments and feedback on previous drafts. This work was supported through NSF Grants AST-0855535 and PHY-1069991 and by the Sherman Fairchild Foundation.
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Sherman Fairchild FoundationUNSPECIFIED
Subject Keywords:binaries: close; gamma-ray burst: general; gravitational waves; stars: magnetic field; stars: neutron
Record Number:CaltechAUTHORS:20120904-134836580
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Official Citation: Magnetic Interactions in Coalescing Neutron Star Binaries Anthony L. Piro 2012 ApJ 755 80
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:33824
Deposited By: Ruth Sustaita
Deposited On:05 Sep 2012 15:12
Last Modified:26 Dec 2012 16:06

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