Multi-messenger Observations of a Binary Neutron Star Merger
Creators: name: LIGO Scientific Collaboration
name: Virgo Collaboration
name: GBM, Fermi
name: INTEGRAL
name: Collaboration, IceCube
name: Team, AstroSat Cadmium Zinc Telluride Imager
name: Collaboration, IPN
name: Collaboration, The Insight-Hxmt
name: Collaboration, ANTARES
name: Collaboration, The Swift
name: Team, AGILE
name: Team, The 1M2H
name: Collaboration, The Dark Energy Camera GW-EM
name: Collaboration, the DES
name: Collaboration, The DLT40
name: GRAWITA
name: :
name: TeAm, GRAvitational Wave Inaf
name: Collaboration, The Fermi Large Area Telescope
name: ATCA
name: :
name: Array, Australia Telescope Compact
name: ASKAP
name: :
name: Pathfinder, Australian SKA
name: Group, Las Cumbres Observatory
name: OzGrav
name: DWF
name: AST3
name: Collaborations, CAASTRO
name: Collaboration, The VINROUGE
name: Collaboration, MASTER
name: J-GEM
name: GROWTH
name: JAGWAR
name: NRAO, Caltech-
name: TTU-NRAO
name: Collaborations, NuSTAR
name: Pan-STARRS
name: Team, The MAXI
name: Consortium, TZAC
name: Collaboration, KU
name: Telescope, Nordic Optical
name: EPESSTO
name: GROND
name: University, Texas Tech
name: Group, SALT
name: TOROS
name: :
name: Collaboration, Transient Robotic Observatory of the South
name: Collaboration, The BOOTES
name: MWA
name: :
name: Array, Murchison Widefield
name: Collaboration, The CALET
name: Collaboration, IKI-GW Follow-up
name: Collaboration, H. E. S. S.
name: Collaboration, LOFAR
name: LWA
name: :
name: Array, Long Wavelength
name: Collaboration, HAWC
name: Collaboration, The Pierre Auger
name: Collaboration, ALMA
name: Team, Euro VLBI
name: Collaboration, Pi of the Sky
name: University, The Chandra Team at McGill
name: DFN
name: :
name: Network, Desert Fireball
name: ATLAS
name: Survey, High Time Resolution Universe
name: RIMAS
name: RATIR
name: Africa/MeerKAT, SKA South
Publisher: name: arXiv
Year: 2017
Subjects: subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: General Relativity and Quantum Cosmology (gr-qc)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: 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 $\sim$1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg$^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 Msun. 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 $\sim$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 $\sim$10 days. Following early non-detections, X-ray and radio emission were discovered at the transient's position $\sim$9 and $\sim$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. (Abridged)
description: This is a reproduction of the article published in the Astrophysical Journal Letters, under the terms of the Creative Commons Attribution 3.0 licence