A Symphony of Giant Monsters Searching for Intermediate-Mass Black Hole Binaries in Advanced LIGO and Advanced Virgo's Third Observing Run

The search for intermediate-mass black holes (IMBHs) has been a focus of astronomers' attention for many years. The Advanced LIGO and Advanced Virgo detectors completed their first two observing runs (O1 and O2) between 2015 and 2017, and no significant detections of IMBH mergers were made. The first half of our third observing run (O3) marked the first confirmed detection of an IMBH remnant in a binary system: GW190521, a discovery which we announced in 2020. In pursuit of finding more such sources, we present here a dedicated IMBH search of the data from O3. In this new search we again found GW190521, but with higher significance. We also found some other possible IMBH candidates, but none qualify as significant. However, the results of our search have improved our understanding of the astrophysical merger rates of IMBH binaries.

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