Analysis of Subthreshold Binary Black Hole Merger Candidates in LIGO O1 and O2 Observing Runs

Posterior datasets and figure creation code for "Analysis of Subthreshold Binary Black Hole Merger Candidates in LIGO O1 and O2 Observing Runs". 

Abstract: 

This study uses data from the LIGO Hanford and Livingston detectors (Abbott et al. 2019) to investigate binary black hole (BBH) merger candidates. 19 candidates were reviewed in total, each having been proposed by either the Institute of Advanced Study (Venumadhav et al. 2019; Zackay et al. 2019a) or the second Open Gravitational-wave catalog (Nitz et al. 2019). Triggers were categorised as significant or insignificant based on studies of posterior distribution consistency with the original detections, coherence tests, and q-transforms. Of the 19 candidates, 14 were identified as significant. Further analysis attempts to identify the formation models that produced each BBH event, such as primordial or hierarchical models. Spin population analysis was one such method used. The method implemented for spin population analysis favoured an isotropic distribution of the effective spin, which in turn could cause the results to favour hierarchical merging. This could offer some explanation to the four candidates identified in the mass gap, the range of masses for which no black holes have been detected, which was proposed by Fishbach & Holz (2017) and has so far been confirmed by LIGO.GW170304 and GW170425, as well as GW170123 and GW170727, warrant further investigation as they could be strongly lensed by a galaxy or galaxy cluster, due to similarities in the calculated parameters.GW170104A requires further investigation as q-transforms showed signal in both detectors, indicating the trigger is of astrophysical origin; however, the IMRPhenomv2 waveform has not correctly modelled the signal.