GW190425 is inconsistent with being a binary neutron star born from a fast merging channel. (arXiv:2001.04502v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Safarzadeh_M/0/1/0/all/0/1">Mohammadtaher Safarzadeh</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ramirez_Ruiz_E/0/1/0/all/0/1">Enrico Ramirez-Ruiz</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Berger_E/0/1/0/all/0/1">Edo Berger</a>

The LIGO/Virgo Scientific Collaboration (LSC) recently announced the
detection of a compact object binary merger, GW190425, with a total mass of
$3.4^{+0.3}_{-0.1}$ M$_{odot}$, and individual component masses in range of
about 1.1 to 2.5 $M_{odot}$. If the constituent compact objects are neutron
stars, then the total mass is five standard deviations higher than the mean of
$2.66pm 0.12$ M$_{odot}$ for Galactic binary neutron stars. The non-detection
of such massive BNS systems in the Galaxy indicates a potential bias against
their detection, which can arise if such massive BNS systems are born with
short orbital periods and hence inspiral times of $sim 10$ Myr. However, we
show that the reported merger rate, $mathcal{R}_{rm
GW190425}=460^{+1050}_{-390}$ yr$^{-1}$ Gpc$^{-3}$, requires extremely high
formation efficiency for such systems of $lambda_{rm f,BNS}=
2times10^{-4}-5times10^{-3}$ M$_{odot}^{-1}$, orders of magnitude larger
than the formation efficiency of fast merging BNS systems from population
synthesis models, $lambda_{rm f,BNS}approx (2-5)times10^{-6}
M_{odot}^{-1}$. Moreover, the comparable merger rates inferred from GW190425
and GW170817 is problematic for two reasons: (i) more massive systems are
expected to have a lower formation rate, and (ii) fast merging channels should
constitute $lesssim 10%$ of the total BNS systems if case BB unstable mass
transfer is permitted to take place as a formation pathway. We argue that to
account for the high merger rate of GW190425 as a BNS system requires: (i) a
change in our understanding NS formation in supernova explosions, or (ii): that
more massive NSs need to be preferentially born with weaker magnetic fields so
that they would be undetectable in the radio surveys. Whether such an
explanation is plausible would require detailed modeling of BNS population with
careful treatment of their magnetic fields evolution.

The LIGO/Virgo Scientific Collaboration (LSC) recently announced the
detection of a compact object binary merger, GW190425, with a total mass of
$3.4^{+0.3}_{-0.1}$ M$_{odot}$, and individual component masses in range of
about 1.1 to 2.5 $M_{odot}$. If the constituent compact objects are neutron
stars, then the total mass is five standard deviations higher than the mean of
$2.66pm 0.12$ M$_{odot}$ for Galactic binary neutron stars. The non-detection
of such massive BNS systems in the Galaxy indicates a potential bias against
their detection, which can arise if such massive BNS systems are born with
short orbital periods and hence inspiral times of $sim 10$ Myr. However, we
show that the reported merger rate, $mathcal{R}_{rm
GW190425}=460^{+1050}_{-390}$ yr$^{-1}$ Gpc$^{-3}$, requires extremely high
formation efficiency for such systems of $lambda_{rm f,BNS}=
2times10^{-4}-5times10^{-3}$ M$_{odot}^{-1}$, orders of magnitude larger
than the formation efficiency of fast merging BNS systems from population
synthesis models, $lambda_{rm f,BNS}approx (2-5)times10^{-6}
M_{odot}^{-1}$. Moreover, the comparable merger rates inferred from GW190425
and GW170817 is problematic for two reasons: (i) more massive systems are
expected to have a lower formation rate, and (ii) fast merging channels should
constitute $lesssim 10%$ of the total BNS systems if case BB unstable mass
transfer is permitted to take place as a formation pathway. We argue that to
account for the high merger rate of GW190425 as a BNS system requires: (i) a
change in our understanding NS formation in supernova explosions, or (ii): that
more massive NSs need to be preferentially born with weaker magnetic fields so
that they would be undetectable in the radio surveys. Whether such an
explanation is plausible would require detailed modeling of BNS population with
careful treatment of their magnetic fields evolution.

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