| Contributors: |
Calloni, E.; De Rosa, Rosario; Garufi, F.; De Laurentis, M.; Di Girolamo, T.; Milano, L.; Barbato, F.; Colalillo, R.; Guarino, Fausto; Valore, L.; Allocca, Annalisa; Gbm, Fermi; Integral; Collaboration, Icecube; Astrosat Cadmium Zinc Telluride Imager Team; Collaboration, Ipn; The Insight-Hxmt Collaboration; Collaboration, Antare; The Swift Collaboration; Team, Agile; The 1m2h Team; The Dark Energy Camera GW-EM Collaboration and the DES Collaboration; The Dlt40 Collaboration; Grawita: Gravitational Wave Inaf Team; The Fermi Large Area Telescope Collaboration; Atca: Australia Telescope Compact Array; Askap: Australian Ska Pathfinder; Las Cumbres Observatory Group; Ozgrav; (Deeper, Dwf; Wider; Program), Faster; Ast3; And Caastro Collaborations; The Vinrouge Collaboration; Collaboration, Master; Growth, J-GEM; Jagwar; Nrao, Caltech-; TTU-NRAO; And Nustar Collaborations; Pan-STARRS; The Maxi Team; Consortium, Tzac; Collaboration, Ku; Nordic Optical Telescope; Grond, Epessto; Texas Tech University; Group, Salt; Toros: Transient Robotic Observatory Of The South Collaboration; The Bootes Collaboration; Mwa: Murchison Widefield Array; The Calet Collaboration; IKI-GW Follow-up Collaboration; Collaboration, H. E. S. S.; Collaboration, Lofar; Lwa: Long Wavelength Array; Collaboration, Hawc; The Pierre Auger Collaboration; Collaboration, Alma; Euro Vlbi Team; Pi Of The Sky Collaboration; The Chandra Team At Mcgill University; Dfn: Desert Fireball Network; Atlas; High Time Resolution Universe Survey; Rimas And Ratir; And Ska South Africa/meerkat; Pinto, Innocenzo; Sequino, Valeria |
| 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 $\sim 1.7\,{\rm{s}}$ 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 ${40}_{-8}^{+8}$ 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 $\,{M}_{\odot }$. 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 $\sim 40\,{\rm{Mpc}}$) 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 ~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. 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 kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta. |