Résumé / Abstract Seminaire_IAP
« GW170817/GRB170817A at 300 days! »

Robert Mochkovitch
Institut d'Astrophysique de Paris (Paris, France)

On August 17, 2017 the LIGO interferometers detected the coalescence of two neutron stars for the first time, at a distance of about 40 Mpc. Due to its orientation with respect to the source, Virgo could not detect the event but was helpful in reducing the size of the error box to 28 square degrees. Less than two seconds after the gravitational wave signal, the Fermi satellite observed a short, weak gamma-ray burst inside the error box. The following day, an optical counterpart – a kilonova – was found in NGC 4993, one of the candidate host galaxies, located at 42 Mpc. An X-ray afterglow was then detected after 9 days, followed by a radio counterpart at 17 days.
After a brief summary of how systems of two neutron stars can form and evolve towards coalescence, I will describe the extraordinary sequence of events, which started 300 days ago and is still ongoing. The gravitational wave signal indicates masses for the two components close to 1.4M0 and a viewing angle below 28 degrees. The gamma-ray burst is underluminous by 5 orders of magnitude compared to regular short GRBs, but still produced photons above 200 keV. The kilonova, a small fraction of neutron-rich material ejected in the merging process and heated by radioactivity appears to be the sum of two components of different masses, velocities and opacities.
Finally the afterglow is atypical, showing a temporal evolution like never observed before.
I will present some of the scenarios that have been proposed to interpret these observations, with a special emphasis on possible models for the afterglow. New events are expected when LIGO/Virgo resume operations at the beginning of next year, though their rates remain quite uncertain. These future events will allow to explore the diversity (both intrinsic or due to differences in viewing angles) of these extraordinary phenomena.
vendredi 15 juin 2018 - 11:00
Amphithéâtre Henri Mineur, Institut d'Astrophysique de Paris
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