LIGO Document P2500067-v7
- This is the third paper of the set recording the results of the suite of tests of general relativity (GR) performed on the signals from the fourth Gravitational-Wave Transient Catalog (GWTC-4.0), where we focus on the remnants of the binary mergers. We examine for the first time 42 events from the first part of the fourth observing run of the LIGO Virgo KAGRA detectors, alongside events from the previous observation runs, restricting our analysis to the confident signals, which were measured in at least two detectors and that have false alarm rates ≤ 10−3 yr−1. This paper focuses on seven tests of the coalescence remnants. Three of these are tests of the ringdown and its consistency with the expected quasi-normal mode (QNM) spectrum of a Kerr black hole. Specifically, two tests analyze just the ringdown in the time domain, and the third test analyzes the entire signal in the frequency domain. Four tests allow for the existence of possible echoes arriving after the end of the ringdown. As such echoes are not expected in GR, we consider two families of proposed waveform templates, and two independent searches
for general excess coherent power after the merger. We find overall consistency of the remnants with GR, and the tightest single-event constraint on the damping time of the dominant (2, 2, 0) QNM of all the GWTC-4.0 events is found for GW231226_101520 by the frequency domain ringdown analysis. When combining events by multiplying likelihoods (hierarchically), that analysis finds that the GR prediction lies at the boundary of the 98.6+1.4−9.4% (99.3+0.7−4.5%) credible region, an increase from 93.8+6.1−20.0% (94.9+4.4 −18.2%) for GWTC-3.0. Here the ranges of values comes from bootstrapping to account for the finite number of events analyzed and suggest
that some of the apparently significant deviation could be attributed to variance due to the finite catalog. Since
the significance also decreases to 92.2% (96.2%) when including the more recent very loud event GW250114, there is no strong evidence for a GR deviation. We find no evidence for post-merger echoes in the events that were analyzed.
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