Deep Follow-up for Gravitational-wave Inference: A Case Study with GW151226

Abstract

New analyses of gravitational-wave events raise questions about the nature of some events. For example, LIGO–Virgo–KAGRA initially determined GW151226 to be a merger with a mass ratio q ≈ 0.5 and effective inspiral spin χ eff ≈ 0.2. However, recent works offer an alternative picture: GW151226 is a lower mass ratio event q ≈ 0.3 with slightly higher spin χ eff ≈ 0.3. This discrepancy has been challenging to resolve, as a wide range of differences are employed for each analysis. This work introduces a “deep follow-up” framework to efficiently compute the posterior odds between two different peaks in parameter space. In doing so, we aim to help resolve disputes about the true nature of gravitational-wave events associated with conflicting astrophysical interpretations. Our proposal is not a replacement for standard inference techniques; instead, our method provides a diagnostic tool to understand discrepancies between conflicting results. We demonstrate this method by studying three q–χ eff peaks proposed for GW151226. We find that the (q ∼ 0.5, χ eff ∼ 0.2) interpretation is only slightly preferred over the (q ∼ 0.3, χ eff ∼ 0.3) hypothesis with posterior odds of ∼1.7 ± 0.4, suggesting that neither of the two peaks can be ruled out. We discuss strategies to produce more reliable parameter estimation studies in gravitational-wave astronomy.