Enhancing the significance of astrophysical events with multimessenger coincidences

TL;DR

This paper presents a Bayesian framework to improve the detection significance of astrophysical events by combining multimessenger data, demonstrated with gravitational waves and neutrinos, significantly increasing confidence in subthreshold detections.

Contribution

The authors develop a formalism for updating the Bayesian probability of astrophysical origin using multimessenger coincidences, applicable to any messenger combination, and demonstrate its effectiveness with real data.

Findings

High-energy neutrino coincidences can raise $p_{astro}$ from ~0.1 to ~0.9

The method enhances confidence in subthreshold detections

Model assumptions influence the degree of probability increase

Abstract

Coincident multimessenger observations of cosmic sources can offer numerous benefits, especially when used in the context of synergistic astrophysics. One significant advantage is enhancing the detection significance of separate detectors by correlating their data and assuming joint emission. We have formulated an approach for updating the Bayesian posterior probability of an astrophysical origin, namely $p_{\rm astro}$, relying on multimessenger coincidences assuming an emission model. The description is applicable to any combination of messengers. We demonstrated the formalism for the gravitational waves and high-energy neutrinos case. Applying our method to the public data of candidate coincident high-energy neutrinos with subthreshold gravitational-wave triggers, we found that in the case of highly energetic neutrino coincidences, $p_{\rm astro}$ can increase from approximately $\sim 0.1$ to $\sim 0.9$. The amount of improvement depends on the assumed joint emission model. If models are trusted, the marked improvement makes subthreshold detections much more confident. Moreover, the model dependency can also be used to test the consistency of different models. This work is a crucial step toward the goal of uniting all detectors on equal footing into a statistically integrated, Earth-sized observatory for comprehensive multimessenger astrophysics.