AGN flares as counterparts to LIGO/Virgo mergers: No confident causal connection in spatial correlation analysis

TL;DR

This study investigates whether AGN flares are causally linked to LIGO/Virgo gravitational wave events, finding no significant spatial correlation and setting an upper limit on their association.

Contribution

It provides a rigorous spatial correlation analysis using updated GW event data and places constraints on the possible connection between AGN flares and GW mergers.

Findings

No significant spatial correlation found between AGN flares and GW events.

Upper limit of 0.155 at 90% credibility on the fraction of GW events related to flares.

Massive GW events with flares are consistent with no causal connection due to localization uncertainties.

Abstract

The primary formation channel for the stellar-mass Binary Black Holes which have been detected merging by the LIGO-Virgo- KAGRA (LVK) collaboration is yet to be discerned. One of the main reason is that the detection of an Electromagnetic counterpart to such Gravitational Wave (GW) events, which could signpost their formation site, has so far been elusive. Recently, 20 Active Galactic Nuclei flaring activities detected by the Zwicky Transient Facility have been investigated as potential counterparts of GW events by Graham et al. (2023). We present the results of a spatial correlation analysis that involves such events and uses the up-to-date posterior samples of 78 mergers, detected during the third observing run of the LVK collaboration. We apply a likelihood method which takes into account the exact position of the flares within the 3D sky map of the GW events. We place an upper limit of 0.155 at a 90 per cent credibility level on the fraction of the detected coalescences that are physically related to an observed flare, whose posterior probability distribution peaks at a null value. Finally, we show that the typically larger values of the masses of the GW-events, which host at least one flare in their localisation volume, are also consistent with the no-connection hypothesis. This is because of a positive correlation between binary masses and the size of the localisation uncertainties.