IAS O3a catalog of binary black hole mergers This is a release of parameter estimation results from the events reported by the IAS-O3a search described in "New binary black hole mergers in the LIGO-Virgo O3a data" (Olsen et al. 2023). We provide posterior samples for all the events identified therein that have probability of astrophysical origin greater than 0.5. This amounts to 42 events, including 10 that had not been reported previously. A summary of this dataset is also being uploaded to the Gravitational Wave Open Science Center's community catalogs. Data products Posterior samples Samples are provided in feather format. Parameters in the posterior samples are as follows: weights: Importance-sampling weight of each sample. f_ref: Frequency of the (l, |m|) = (2, 2) mode at which the initial condition is specified (Hz). m1: Detector-frame primary mass (solar masses). m2: Detector-frame secondary mass (solar masses). iota: Inclination angle (rad). s1x: Dimensionless spin of the primary in the x direction. s1y: Dimensionless spin of the primary in the y direction. s1z: Dimensionless spin of the primary in the z direction. s1x_n: Dimensionless spin of the primary in the x_n direction. s1y_n: Dimensionless spin of the primary in the y_n direction. s2x: Dimensionless spin of the secondary in the x direction. s2y: Dimensionless spin of the secondary in the y direction. s2x_n: Dimensionless spin of the secondary in the x_n direction. s2y_n: Dimensionless spin of the secondary in the y_n direction. s2z: Dimensionless spin of the secondary in the z direction. d_luminosity: Luminosity distance (Mpc). ra: Right ascension (rad). dec: Declination (rad). phi_ref: Orbital phase at the reference frequency (rad). psi: Polarization angle (rad). t_geocenter: Arrival time at the center of Earth relative to tgps (s). mchirp: Detector-frame chirp mass (solar masses). chieff: Effective spin. mtot: Detector-frame total mass (solar masses). redshift: Cosmological redshift. m1_source: Source-frame primary mass (solar masses). m2_source: Source-frame secondary mass (solar masses). mchirp_source: Source-frame chirp mass (solar masses). mtot_source: Source-frame total mass (solar masses). lnl: Log-likelihood. Coordinate systems: (x, y, z) are the standard LAL coordinates, where x is along the separation of the two objects at f_ref, and z is along the orbital angular momentum, see https://lscsoft.docs.ligo.org/lalsuite/lalsimulation/group__lalsimulation__inference.html (x_n, y_n) are rotated with respect to (x, y) by an angle phi_ref; thus, these axes are defined in terms of the orbital angular momentum and the line of sight without regard to the orbital separation vector. Events are analyzed under two different priors (here referred to as "IAS" and "LVC"). These only differ in the spin distribution (the IAS prior is uniform in effective spin, the LVC prior is uniform in spin magnitudes and isotropic in spin orientations). In both cases, the prior for the masses is uniform in detector-frame component masses and uniform in comoving volume-time. Parameter inferences were done with the software cogwheel (Roulet et al. 2022, 2024), using to the stochastic samplers Nautilus (Lange 2023), or Zeus (Karamanis et al. 2020, 2021) for GW190910_012619. The waveform approximant used is IMRPhenomXPHM (Pratten et al. 2020). Note: All 42 events in the catalog were reanalyzed for this release. In this analysis, we find that GW190910_012619 has a second mode that was absent in the original publication (Olsen et al. 2023); other results are similar. Strain data For each event, the strain data is provided in npz format, see the usage demo for how to load it. For a few events, glitches have been inpainted. The file inpaint_times.json contains the times at which each event and detector was inpainted, measured in seconds from the GPS time of that event. Events metadata The following summary information from the search pipeline is provided in events_metadata.json: ifar_yr: Inverse false-alaram rate (y). pastro: Probability of astrophysical origin. gracedb_id: If available, corresponding entry in GraceDB. tgps: GPS time. snr: Signal-to-noise ratio achieved by the trigger in the search, in the Hanford-Livingston network. Authors This release was prepared by Javier Roulet and Ajit Kumar Mehta. The IAS-O3a search was carried out by Seth Olsen, Tejaswi Venumadhav, Jonathan Mushkin, Javier Roulet, Barak Zackay and Matias Zaldarriaga. Related products IAS-O3a catalog paper: arXiv, PRD IAS-O3a search data products: GitHub Acknowledgements This research has made use of data or software obtained from the Gravitational Wave Open Science Center (gwosc.org), a service of the LIGO Scientific Collaboration, the Virgo Collaboration, and KAGRA. This material is based upon work supported by NSF's LIGO Laboratory which is a major facility fully funded by the National Science Foundation, as well as the Science and Technology Facilities Council (STFC) of the United Kingdom, the Max-Planck-Society (MPS), and the State of Niedersachsen/Germany for support of the construction of Advanced LIGO and construction and operation of the GEO600 detector. Additional support for Advanced LIGO was provided by the Australian Research Council. Virgo is funded, through the European Gravitational Observatory (EGO), by the French Centre National de Recherche Scientifique (CNRS), the Italian Istituto Nazionale di Fisica Nucleare (INFN) and the Dutch Nikhef, with contributions by institutions from Belgium, Germany, Greece, Hungary, Ireland, Japan, Monaco, Poland, Portugal, Spain. KAGRA is supported by Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan Society for the Promotion of Science (JSPS) in Japan; National Research Foundation (NRF) and Ministry of Science and ICT (MSIT) in Korea; Academia Sinica (AS) and National Science and Technology Council (NSTC) in Taiwan.