New binary black hole mergers in the LIGO-Virgo O3a data

We report the detection of ten new binary black hole (BBH) mergers in the publicly released data from the first half of the third observing run (O3a) of advanced LIGO and advanced Virgo. We identify candidates using an updated version of the search pipeline described in Venumadhav et al. [Phys. Rev. D 100, 023011 (2019)PRVDAQ2470-001010.1103/PhysRevD.100.023011] (the "IAS pipeline"[T. Venumadhav, Phys. Rev. D 101, 083030 (2020).PRVDAQ2470-001010.1103/PhysRevD.101.083030]) and compile a catalog of signals that pass a significance threshold of astrophysical probability greater than 0.5 (following the GWTC-2.1 [R. Abbott (The LIGO Scientific Collaboration, the Virgo Collaboration), arXiv:2108.01045.] and 3-OGC [A. H. Nitz, Astrophys. J. 922, 76 (2021).ASJOAB0004-637X10.3847/1538-4357/ac1c03] catalogs). The updated IAS pipeline is sensitive to a larger region of parameter space, applies a template prior that accounts for different search volume as a function of intrinsic parameters, and uses an improved coherent detection statistic that optimally combines the data from the Hanford and Livingston detectors. Among the ten new events, we observe interesting astrophysical scenarios including sources with confidently large effective spin parameters in both the positive and negative directions, high-mass black holes that are difficult to form in stellar collapse models due to (pulsational) pair instability, and low-mass mergers that bridge the gap between neutron stars and the lightest observed black holes. We infer source parameters in the upper and lower black hole mass gaps with both extreme and near-unity mass ratios, and one of the possible neutron star-black hole (NSBH) mergers is well localized for electromagnetic (EM) counterpart searches. We detect all of the GWTC-2.1 BBH mergers with coincident data in Hanford and Livingston except for three loud events that get vetoed, which is compatible with the false-positive rate of our veto procedure, and three that fall below the detection threshold. We also return to significance the event GW190909_114149, which was reduced to a subthreshold trigger after its initial appearance in GWTC-2 [R. Abbott, Phys. Rev. X 11, 021053 (2021).PRXHAE2160-330810.1103/PhysRevX.11.021053]. This amounts to a total of 42 BBH mergers detected by our pipeline's search of the coincident Hanford-Livingston O3a data.