Welcome by LNF Director, Dr. P. Campana Room: Aula Bruno Touschek

Observation of Gravitational Waves from a Binary Neutron Star Merger

• Gianluca Gemme (INFN Sezione di Genova)

Room: Aula Bruno Touschek On August 17, 2017 the Advanced LIGO and Advanced Virgo detectors discovered a gravitational-wave signal (GW170817) consistent with a binary neutron star (BNS) inspiral. Almost simultaneously, a gamma-ray burst (GRB 170817A) was observed independently by the Fermi Gamma-ray Burst Monitor, and the Anticoincidence Shield for the Spectrometer for the International Gamma-Ray Astrophysics Laboratory. GW170817 is the loudest (highest signal-to-noise ratio) and closest gravitational-wave event observed so far. The LIGO and Virgo data produced a three-dimensional sky localization of the source, enabling a successful electromagnetic follow-up campaign that identified an associated electromagnetic transient in a galaxy ~40 Mpc from Earth. A multi-messenger view of GW170817 from ~100 seconds before merger through weeks afterward provides unprecedented insight into these events. For the first time, using gravitational waves we are able to constrain the equation of state of dense neutron stars and infer the rate of local binary neutron star mergers. When we include EM observations, we are able to independently measure the Hubble constant, probe the validity of the equivalence principle, gain new insight into the engine driving these events, and other ground-breaking fundamental results.

The Electromagnetic Follow-up

• Enzo Brocato (INAF - Osservatorio Astronomico di Roma)

Room: Aula Bruno Touschek The alert provided by the Advanced LIGO and Advanced Virgo detectors on August 17, 2017 triggered one of the most extensive campaign in the history of the observational astrophysics. The contemporaneity of the gravitational wave event GW170817, with high energy photons measured by space missions (FERMI and INTEGRAL), was early established and the localization of the electromagnetic counterpart (AT2017gfo) was performed within ~11 hours. The characterization of the physical properties of this sources required a large international effort involving 8-m class telescopes and a wide time coverage. The electromagnetic follow-up of GW170817 provided evidences that the merging of two neutron stars give rise to a transient optical/near-infrared source, named “kilonova”. This source is expected to be powered by the synthesis of heavy elements via rapid neutron capture (the r-process). Comparison with spectral models suggests that the observed merger ejected a quantity of matter of the order of 0.03-0.05 solar masses.