# Observation of gravitational waves from two neutron star–black hole coalescences

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LIGO-P2000357-v9
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P - Publications
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Abstract:
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 $$8.9^{+1.2}_{-1.5}\,M_\odot$$ and $$1.9^{+0.3}_{-0.2}\,M_\odot$$, whereas the source of GW200115 has component masses $$5.7^{+1.8}_{-2.1}\,M_\odot$$ and $$1.5^{+0.7}_{-0.3}\,M_\odot$$ (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 $$300^{+150}_{-100}$$ 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 spin or tidal deformation of the secondary component for either event. We infer a NSBH merger rate density of $$45^{+75}_{-33}\,\mathrm{Gpc}^{-3} \mathrm{yr}^{-1}$$ when assuming GW200105 and GW200115 are representative of the NSBH population, or $$130^{+112}_{-69}\,\mathrm{Gpc}^{-3} \mathrm{yr}^{-1}$$ under the assumption of a broader distribution of component masses.
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GW200105 GW200115 NSBH
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Version uploaded to arXiv, identical to the one in ApJL, except for typesetting.
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Published in ApJ Letters vol. 915 pg. L5.

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