2020ApJ...890..135N

We discuss a technique for detecting and locating rapid transient electromagnetic counterparts to gravitational wave sources that affords a reprieve of several hours after the gravitational wave event. The technique relies on detecting a scattering halo produced if X-rays emitted at the gravitational wave event scatter off Galactic dust clouds. The travel-time delay of these scattered photons makes them detectable up to several hours after the prompt event; the location of the gravitational wave source will be at the geometric center of the halo, which can be determined with precision sufficient to allow the host galaxy to be identified.