What are the electromagnetic counterparts of compact object mergers?

The first detection of gravitational waves from a binary black hole in 2015 verified a key prediction from Einstein’s Theory of General Relativity. Soon after, the first detection of a binary neutron merger in 2017 in both ‘cosmic messengers‘ of gravitational waves and light heralded the dawn of multi-messenger gravitational-wave astrophysics. Telescope observations of this binary neutron star merger across the electromagnetic spectrum revealed an astounding array of phenomena, including a short Gamma-ray burst and a kilonova (see Figure below). However, many aspects of this event remain puzzling, and require telescope observations of more compact object mergers to fully characterize their electromagnetic counterparts. To obtain multi-wavelength observations of these counterpart, we must use telescopes to conduct a rapid hunt for the counterpart immediately after the gravitational wave detection.

The optical kilonova counterpart of the first binary neutron star merger GW170817 as observed by the Hubble Space Telescope (background), and the X-ray afterglow of the accompanying short Gamma-ray burst as observed by the Chandra X-ray Observatory (insets).

***The X-ray afterglow surprisingly brightened over several months after the merger, unlike any other short Gamma-ray burst afterglow ever observed (Ruan et al., 2018).***
*Image credit: Daryl Haggard*

My team is leading a Canadian effort to localize the electromagnetic counterparts of compact object mergers detected in gravitational waves. Specifically, we lead ongoing programs to use wide-field optical imaging on the Canada-France-Hawaii Telescope to quickly tile the gravitational wave localization of new binary neutron star mergers after they are detected by the LIGO/Virgo gravitational wave interferometers. We then process these images using our custom imaging differencing and transient detection software to search for a kilonova counterpart.