Abstract
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 . 5 + 1. 2 and 1. 9 − 0. 2 + 0. 3 M ⊙ , whereas the source of GW200115 has component masses 5. 7 − 2 . 1 + 1. 8 and 1. 5 − 0. 3 + 0. 7 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 − 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 the spin or tidal deformation of the secondary component for either event. We infer an NSBH merger rate density of 45 − 33 + 75 Gpc − 3 yr − 1 when assuming that GW200105 and GW200115 are representative of the NSBH population or 130 − 69 + 112 Gpc − 3 yr − 1 under the assumption of a broader distribution of component masses.
Highlights
In 2020 January, the LIGO–Virgo detector network observed gravitational-wave (GW) signals from two compact binary inspirals that are consistent with neutron star–black hole (NSBH) binaries
Event GW200115 was initially identified by all four lowlatency matched-filtering pipelines as a possible compact binary coalescence (CBC) candidate in LIGO Hanford and LIGO Livingston: GSTLAL (Cannon et al 2012; Privitera et al 2014; Messick et al 2017; Sachdev et al 2019; Hanna et al 2020), MBTA ONLINE (Adams et al 2016; Aubin et al 2021), PYCBC LIVE (Usman et al 2016; Nitz et al 2017, 2018, 2019a; Dal Canton et al 2020), and SPIIR (Hooper et al 2012; Luan et al 2012; Guo et al 2018; Chu et al 2020)
To highlight how the secondary masses of GW200105 and GW200115 compare to the maximum NS mass, we show two estimates of the maximum
Summary
In 2020 January, the LIGO–Virgo detector network observed gravitational-wave (GW) signals from two compact binary inspirals that are consistent with neutron star–black hole (NSBH) binaries. While quantification of the confidence of single-detector events is subject to significant uncertainty, GW200105 stands clearly apart in the LIGO Livingston data from any other candidate with NSBH-like parameters during the ∼11 months of the third observing run (O3). Light-scattering noise (Soni et al 2020, 2021) is visible in Figure 1 in LIGO Livingston around 20 Hz. The LIGO and Virgo GW detectors are calibrated using radiation pressure from auxiliary lasers at a known frequency and amplitude (Acernese et al 2018; Sun et al 2020). To verify that instrumental noise artifacts do not bias the analysis of source properties of the observed events, we use data quality validation procedures as in previous events (Abbott et al 2016e; Davis et al 2021), employing sensor arrays at LIGO and Virgo to measure environmental disturbances that could couple into the interferometers (Nguyen et al 2021). An asterisk indicates values where Virgo is not included in the S/N calculation
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