Deep Hubble Space Telescope Observations of GW170817: Complete Light Curves and the Properties of the Galaxy Merger of NGC 4993

Understand

We present the complete set of {\it Hubble Space Telescope} imaging of the binary neutron star merger GW170817 and its optical counterpart AT 2017gfo.

• Including deep template imaging in F814W, F110W, F140W, and F160W at 3.4 years post-merger, we re-analyze the full light curve of AT 2017gfo across 12 bands from 5--1273 rest-frame days after merger.
• We obtain four new detections of the short $\gamma$-ray burst (GRB) 170817A afterglow from 109--170 rest-frame days post-merger.
• These detections are consistent with the previously observed $\beta=-0.6$ spectral index in the afterglow light curve with no evidence for spectral evolution.