NGC 4993, the shell galaxy host of GW170817: constraints on the recent galactic merger

Understand

NGC 4993 is the shell galaxy host of the GRB170817A short gamma-ray burst and the GW170817 gravitational-wave event produced during a binary-neutron-star coalescence.

• The galaxy shows signs, including the stellar shells, that it has recently accreted a smaller, late-type galaxy.
• The accreted galaxy might be the original host of the binary neutron star.
• We measured the positions of the stellar shells of NGC 4993 in an HST/ACS archival image and use the shell positions to constrain the time of the galactic merger.