Fong Subproject for Late-time Monitoring of GW170817 Across the Electromagnetic Spectrum

We propose joint Chandra-VLA-HST observations to continue our monitoring of the binary neutron star merger GW170817 at t~500-850 days since merger. Our immediate objectives are: (i) to constrain the broad-band spectral evolution of the non-thermal emission from GW170817, and, in particular, the passage of the synchrotron cooling frequency within the Chandra bandpass; (ii) to map the temporal evolution of the emission from GW170817 across the electromagnetic spectrum. These observations are designed to provide new insight into the current debate about the nature of the relativistic ejecta of compact-object mergers and their (now questioned) capability to successfully launch ultra-relativistic jets in their environment.