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+1.2-1.5 and 1.9+.03-.02 M⊙, whereas the source of GW200115 has component masses and 5.7+1.8-2.1 and 1.5+0.7-0.3 M⊙ (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 and 300+150-100 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 the spin or tidal deformation of the secondary component for either event. We infer an NSBH merger rate density of 45+75-33 Gpc-3 yr-1 when assuming that GW200105 and GW200115 are representative of the NSBH population or 130 +112-69 Gpc-3 yr-1 under the assumption of a broader distribution of component masses.
R. Abbott et al., "Observation of Gravitational Waves from Two Neutron Star-Black Hole Coalescences," Astrophysical Journal Letters, vol. 915, no. 1, article no. L5, IOP Publishing, Jul 2021.
The definitive version is available at https://doi.org/10.3847/2041-8213/ac082e
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01 Jul 2021