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http://arxiv.org/abs/1101.4298

Luciano Rezzolla, Bruno Giacomazzo, Luca Baiotti, Jonathan Granot, Chryssa Kouveliotou, Miguel A. Aloy

(Submitted on 22 Jan 2011)

"Short Gamma-Ray Bursts (SGRBs) are among the most luminous explosions in the universe, releasing in less than one second the energy emitted by our Galaxy over one year. Despite decades of observations, the nature of their "central-engine" remains unknown. Considering a binary of magnetized neutron stars and solving Einstein equations, we show that their merger results in a rapidly spinning black hole surrounded by a hot and highly magnetized torus. Lasting over 35 ms and much longer than previous simulations, our study reveals that magnetohydrodynamical instabilities amplify an initially turbulent magnetic field of ~ 10

Published version in ApJL; for high-resolution images and animations see this webpage:

http://numrel.aei.mpg.de/images/relativistic-binary-neutron-star-inspirals

see also this Science Daily article:

http://www.sciencedaily.com/releases/2011/04/110407132618.htm

Also this followup article by some of the same AEI authors:

http://arxiv.org/abs/1103.3874

Luca Baiotti, Thibault Damour, Bruno Giacomazzo, Alessandro Nagar, Luciano Rezzolla

25 pages, 16 figs

(Submitted on 20 Mar 2011)

"Binary neutron-star systems represent one of the most promising sources of gravitational waves. In order to be able to extract important information, notably about the equation of state of matter at nuclear density, it is necessary to have in hands an accurate analytical model of the expected waveforms. Following our recent work, we here analyze more in detail two general-relativistic simulations spanning about 20 gravitational-wave cycles of the inspiral of equal-mass binary neutron stars with different compactnesses, and compare them with a tidal extension of the effective-one-body (EOB) analytical model. The latter tidally extended EOB model is analytically complete up to the 1.5 post-Newtonian level, and contains an analytically undetermined parameter representing a higher-order amplification of tidal effects. We find that, by calibrating this single parameter, the EOB model can reproduce, within the numerical error, the two numerical waveforms essentially up to the merger. By contrast, analytical models (either EOB, or Taylor-T4) that do not incorporate such a higher-order amplification of tidal effects, build a dephasing with respect to the numerical waveforms of several radians."

**The missing link: Merging neutron stars naturally produce jet-like structures and can power short Gamma-Ray Bursts**Luciano Rezzolla, Bruno Giacomazzo, Luca Baiotti, Jonathan Granot, Chryssa Kouveliotou, Miguel A. Aloy

(Submitted on 22 Jan 2011)

"Short Gamma-Ray Bursts (SGRBs) are among the most luminous explosions in the universe, releasing in less than one second the energy emitted by our Galaxy over one year. Despite decades of observations, the nature of their "central-engine" remains unknown. Considering a binary of magnetized neutron stars and solving Einstein equations, we show that their merger results in a rapidly spinning black hole surrounded by a hot and highly magnetized torus. Lasting over 35 ms and much longer than previous simulations, our study reveals that magnetohydrodynamical instabilities amplify an initially turbulent magnetic field of ~ 10

^{12}G to produce an ordered poloidal field of ~ 10^{15}G along the black-hole spin-axis, within a half-opening angle of ~ 30 deg, which may naturally launch a relativistic jet. The broad consistency of our ab-initio calculations with SGRB observations shows that the merger of magnetized neutron stars can provide the basic physical conditions for the central-engine of SGRBs."Published version in ApJL; for high-resolution images and animations see this webpage:

http://numrel.aei.mpg.de/images/relativistic-binary-neutron-star-inspirals

see also this Science Daily article:

http://www.sciencedaily.com/releases/2011/04/110407132618.htm

Also this followup article by some of the same AEI authors:

http://arxiv.org/abs/1103.3874

**Accurate numerical simulations of inspiralling binary neutron stars and their comparison with effective-one-body analytical models**Luca Baiotti, Thibault Damour, Bruno Giacomazzo, Alessandro Nagar, Luciano Rezzolla

25 pages, 16 figs

(Submitted on 20 Mar 2011)

"Binary neutron-star systems represent one of the most promising sources of gravitational waves. In order to be able to extract important information, notably about the equation of state of matter at nuclear density, it is necessary to have in hands an accurate analytical model of the expected waveforms. Following our recent work, we here analyze more in detail two general-relativistic simulations spanning about 20 gravitational-wave cycles of the inspiral of equal-mass binary neutron stars with different compactnesses, and compare them with a tidal extension of the effective-one-body (EOB) analytical model. The latter tidally extended EOB model is analytically complete up to the 1.5 post-Newtonian level, and contains an analytically undetermined parameter representing a higher-order amplification of tidal effects. We find that, by calibrating this single parameter, the EOB model can reproduce, within the numerical error, the two numerical waveforms essentially up to the merger. By contrast, analytical models (either EOB, or Taylor-T4) that do not incorporate such a higher-order amplification of tidal effects, build a dephasing with respect to the numerical waveforms of several radians."

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