Observation of Gravitational Waves from Two Neutron Star-Black Hole Coalescences

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Abbott, R 
Abbott, TD 
Abraham, S 
Acernese, F 
Ackley, K 

We report the observation of gravitational waves from two compact binary coalescences in LIGO's and Virgo's third observing run with properties consistent with neutron star-black hole (NSBH) binaries. The two events are named GW200105_162426 and GW200115_042309, abbreviated as GW200105 and GW200115; the first was observed by LIGO Livingston and Virgo, and the second by all three LIGO-Virgo detectors. The source of GW200105 has component masses 8.9−1.5+1.2M and 1.9−0.2+0.3M, whereas the source of GW200115 has component masses 5.7−2.1+1.8M and 1.5−0.3+0.7M (all measurements quoted at the 90% credible level). The probability that the secondary's mass is below the maximal mass of a neutron star is 89%-96% and 87%-98%, respectively, for GW200105 and GW200115, with the ranges arising from different astrophysical assumptions. The source luminosity distances are 280−110+110 Mpc and 300−100+150 Mpc, respectively. The magnitude of the primary spin of GW200105 is less than 0.23 at the 90% credible level, and its orientation is unconstrained. For GW200115, the primary spin has a negative spin projection onto the orbital angular momentum at 88% probability. We are unable to constrain spin or tidal deformation of the secondary component for either event. We infer a NSBH merger rate density of 45−33+75Gpc−3yr−1 when assuming GW200105 and GW200115 are representative of the NSBH population, or 130−69+112Gpc−3yr−1 under the assumption of a broader distribution of component masses.

astro-ph.HE, astro-ph.HE
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Astrophysical Journal Letters
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American Astronomical Society