W170817/GRB 170817A/AT2017gfo: A Tryptich of Rosetta Stones for Compact Object Astrophysics

On the 17th of August 2017, an astronomical event occurred which represents a watershed in our understanding of neutron stars. The LIGO and Virgo gravitational-wave observatories detected the first compact binary inspiral produced by two neutron stars, which was followed about two seconds later by a short GRB, labelled GRB 170817A, detected by the GBM instrument on Fermi. The detection by all three GW observatories allowed the error region to be strongly reduced in size, and the distance information inherent in the inspiral signal allowed a dedicated follow-up campaign to discover an optical counterpart less than half a day after the event, situated in the S0 elliptical galaxy NGC 4993. This optical transient turned out not to be a classical GRB afterglow, but instead a so-called Kilonova powered by the radioactive decay of heavy elements created by the r-process. In a single event, conclusive evidence has been found that short GRBs have neutron star mergers as their progenitors, that Kilonovae have structured ejecta, and that they produce a large fraction of elements beyond the iron group in the Universe.

02/11/2017 - 12:30
Dr. David Alexander Kann