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Multi-Messenger Observations of a Binary Neutron Star Merger

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Journal Article - Open Access

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On 2017 August 17 a binary neutron star coalescence candidate later designated GW170817 with merger time 124104 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst GRB 170817A with a time delay of approx. 1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40-88 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 M . An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient SSS17a, now with the IAU identification of AT 2017gfo in NGC 4993 at approx. 40 Mpc less than 11 hours after the merger by the One-Meter, Two Hemisphere 1M2H team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over approx.10 days. Following early non-detections, X-ray and radio emission were discovered at the transients position approx 9 and approx 16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UVopticalnear-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC 4993 followed by a short gamma-ray burst GRB 170817A and a kilonovamacronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta.

Subject Categories:

  • Astronomy
  • Cybernetics
  • Optical Detection and Detectors

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