Multi-messenger Observations of a Binary Neutron Star Merger

LIGO Sci Collaboration & Virgo ; Fermi GBM ; INTERGRAL ; IceCube Collaboration ; AstroSat Cadmium Zinc Telluride ; IPN Collaboration ; Insight-Hxmt Collaboration ; ANTARES Collaboration ; Swift Collaboration ; AGILE Team ; The 1M2H Team ; Dark Energy Camera GW-EM ; DLT40 Collaboration ; GRAWITA GRAvitational Wave ; Fermi Large Area Telescope ; ATCA Australia Telescope ; ASKAP Australian SKA Pathfinder ; Las Cumbres Observatory Grp ; OzGrav DWF Deeper Wider Faster ; VINROUGE Collaboration ; MASTER Collaboration ; J-GEM ; GROWTH JAGWAR CALTECH ; Pan-STARRS ; MAXI Team ; TZAC Consortium ; KU Collaboration ; Nordic Optical Telescope ; ePESSTO ; GROUND ; Texas Tech Univ ; Salt Grp ; Toros Transient Robotic Observat ; BOOTES Collaboration ; MWA Murchison Widefield Array ; CALET Collaboration ; IKI-GW Follow-up Collaboration ; H E S S Collaboration ; LOFAR Collaboration ; LWA Long Wavelength Array ; HAWC Collaboration ; Pierre Auger Collaboration ; ALMA Collaboration ; Euro VLBI Team ; Pi Sky Collaboration ; Chandra Team McGill Univ ; DFN Desert Fireball Network ; ATLAS ; High Time Resolution Universe ; RIMAS RATIR ; SKA South Africa MeerKAT. 2017. Multi-messenger Observations of a Binary Neutron Star Merger. Astrophysical Journal Letters 848, 2, DOI: 10.3847/2041-8213/aa91c9

On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 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 similar to 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 deg(2) at a luminosity distance of 40(-8)(+8) 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-circle dot. 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 similar to 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 similar to 10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position similar to 9 and similar to 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 UV/optical/near-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 NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta.

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