Gravitational waves and mass ejecta from binary neutron star mergers: Effect of the mass ratio

Gravitational Waves (GW) from coalescence of a Binary Neutron Star (BNS) and its accompanying short Gamma-Ray Burst (GRB) GW/GRB 170817A confirmed the presumed origin of these puzzling transients and opened up the way for relating properties of short GRBs to those of their progenitor stars and their surroundings. Here we review an extensive analysis of the prompt gamma-ray and late afterglows of this event. We show that a fraction of polar ejecta from the merger had been accelerated to ultra-relativistic speeds. This structured jet had an initial Lorentz factor of about 260 in our direction, which was O ( 10 ∘ ) from the jet’s axis, and was a few orders of magnitude less dense than in typical short GRBs. At the time of arrival to circum-burst material the ultra-relativistic jet had a close to Gaussian profile and a Lorentz factor ≳ 130 in its core. It had retained in some extent its internal collimation and coherence, but had extended laterally to create mildly relativistic lobes—a cocoon. Its external shocks on the far from center inhomogeneous circum-burst material and low density of colliding shells generated slowly rising afterglows, which peaked more than 100 days after the prompt gamma-ray. The circum-burst material was somehow correlated with the merger. As non-relativistic outflows or tidally ejected material during BNS merger could not have been arrived to the location of the external shocks before the relativistic jet, circum-burst material might have contained recently ejected materials from resumption of internal activities, faulting and mass loss due to deformation and breaking of stars crusts by tidal forces during latest stages of their inspiral but well before their merger. By comparing these findings with the results of relativistic Magneto-Hydro-Dynamics (MHD) simulations and observed gravitational waves we conclude that progenitor neutron stars were most probably old, had close masses and highly reduced magnetic fields.

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X-RAY COUNTERPART OF GRAVITATIONAL WAVES DUE TO BINARY NEUTRON STAR MERGERS: LIGHT CURVES, LUMINOSITY FUNCTION, AND EVENT RATE DENSITY

The Astrophysical Journal ◽

10.3847/1538-4357/835/1/7 ◽

2017 ◽

Vol 835 (1) ◽

pp. 7 ◽

Cited By ~ 31

Author(s):

Hui Sun ◽

Bing Zhang ◽

He Gao

Keyword(s):

Neutron Star ◽

Gravitational Waves ◽

Luminosity Function ◽

Event Rate ◽

Light Curves ◽

X Ray ◽

Binary Neutron Star

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UTILITY OF GALAXY CATALOGS FOR FOLLOWING UP GRAVITATIONAL WAVES FROM BINARY NEUTRON STAR MERGERS WITH WIDE-FIELD TELESCOPES

The Astrophysical Journal ◽

10.1088/0004-637x/784/1/8 ◽

2014 ◽

Vol 784 (1) ◽

pp. 8 ◽

Cited By ~ 32

Author(s):

Chad Hanna ◽

Ilya Mandel ◽

Will Vousden

Keyword(s):

Neutron Star ◽

Gravitational Waves ◽

Wide Field ◽

Binary Neutron Star

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Gravitational waves from post-merger radially oscillating millisecond pulsars

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834552 ◽

2019 ◽

Vol 622 ◽

pp. A194 ◽

Cited By ~ 2

Author(s):

Z. G. Dai

Keyword(s):

Neutron Star ◽

Gravitational Waves ◽

High Frequency ◽

Gamma Ray ◽

Magnitude Estimate ◽

Compact Objects ◽

Millisecond Pulsars ◽

Binary Neutron Star ◽

Order Of Magnitude ◽

Negligible Contribution

Observations of short-duration gamma-ray bursts and their afterglows show that a good fraction (perhaps ≳50%) of binary neutron star mergers lead to strongly magnetized, rapidly rotating pulsars (including millisecond magnetars), no matter whether the pulsar remnants are short- or long-lived. Such compact objects are very likely to have significant radial oscillations and high interior temperatures, as indicated in recent numerical simulations. In this paper, we have investigated rotation-induced gravitational radiation from possibly existing, radially oscillating pulsars after binary neutron star mergers, and find that this mechanism can efficiently damp the radial oscillations. The resulting gravitational waves (GWs) could have a non-negligible contribution to the high-frequency spectrum. We provide an order-of-magnitude estimate of the event rate and suggest that such GW events would be detectable with the advanced LIGO/Virgo or next-generation detectors. Our discussion can also be applied to newborn, radially oscillating, millisecond pulsars formed through the other astrophysical processes.

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