Verification of proposed electromagnetic counterparts for compact binary mergers

Establish whether the various proposed electromagnetic emissions associated with binary neutron star, neutron star–black hole, and binary black hole mergers are genuinely produced by these systems and can be robustly identified as counterparts to gravitational-wave events, thereby enabling their reliable use as bright standard sirens.

Background

The bright siren method relies on identifying electromagnetic counterparts to gravitational-wave sources in order to obtain precise redshifts via host galaxies. While GW170817 established this for a binary neutron star event, a wide range of additional electromagnetic emission mechanisms have been proposed across different compact-binary classes.

The authors note that, despite theoretical proposals and some observational suggestions, these other counterparts have not been confidently verified. Confirming their existence and association with compact binary mergers would expand the applicability and precision of bright siren cosmology.