Characterizing Astrophysical Binary Neutron Stars with Gravitational Waves. (arXiv:2007.08198v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Zhu_X/0/1/0/all/0/1">Xing-Jiang Zhu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ashton_G/0/1/0/all/0/1">Gregory Ashton</a>
Merging binary neutron stars are thought to be formed predominantly via
isolated binary evolution. In this standard formation scenario, the first-born
neutron star goes through a recycling process and might be rapidly spinning
during the final inspiral, whereas the second-born star is expected to have
effectively zero spin at merger. Based on this feature, we propose a new
framework for the astrophysical characterization of binary neutron stars
observed from their gravitational wave emission. We further propose a prior for
the dimensionless spin magnitudes of recycled neutron stars, given by a gamma
distribution with a shape parameter of 2 and a scale parameter of 0.012, from
radio pulsar observations of Galactic binary neutron stars. Interpreting
GW170817 and GW190425 in the context of the standard formation scenario, we
find positive support for a spinning recycled neutron star (with a spin tilt
angle $lesssim 60^{circ}$) in GW190425 with a Bayes factor of 6, whereas the
spin of the recycled neutron star in GW170817 is small and consistent with our
prior. We measure the mass of the recycled (slow) neutron star in GW170817 and
GW190425 to be $1.34_{-0.09}^{+0.12}$ ($1.38_{-0.11}^{+0.11}$) $M_{odot}$ and
$1.64_{-0.11}^{+0.13}$ ($1.66_{-0.12}^{+0.12}$) $M_{odot}$, with $68%$
credibility, respectively. The mass ratio of GW170817 (GW190425) is constrained
to be between 0.79 (0.80) and 1, with 90% credibility.
Merging binary neutron stars are thought to be formed predominantly via
isolated binary evolution. In this standard formation scenario, the first-born
neutron star goes through a recycling process and might be rapidly spinning
during the final inspiral, whereas the second-born star is expected to have
effectively zero spin at merger. Based on this feature, we propose a new
framework for the astrophysical characterization of binary neutron stars
observed from their gravitational wave emission. We further propose a prior for
the dimensionless spin magnitudes of recycled neutron stars, given by a gamma
distribution with a shape parameter of 2 and a scale parameter of 0.012, from
radio pulsar observations of Galactic binary neutron stars. Interpreting
GW170817 and GW190425 in the context of the standard formation scenario, we
find positive support for a spinning recycled neutron star (with a spin tilt
angle $lesssim 60^{circ}$) in GW190425 with a Bayes factor of 6, whereas the
spin of the recycled neutron star in GW170817 is small and consistent with our
prior. We measure the mass of the recycled (slow) neutron star in GW170817 and
GW190425 to be $1.34_{-0.09}^{+0.12}$ ($1.38_{-0.11}^{+0.11}$) $M_{odot}$ and
$1.64_{-0.11}^{+0.13}$ ($1.66_{-0.12}^{+0.12}$) $M_{odot}$, with $68%$
credibility, respectively. The mass ratio of GW170817 (GW190425) is constrained
to be between 0.79 (0.80) and 1, with 90% credibility.
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