Multi-messenger Observations of a Binary Neutron Star Merger^*

Abstract

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 ∼ 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 − 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 ⊙ . 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 ∼ 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 ∼10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ∼ 9 and ∼ 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.

The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. II. UV, Optical, and Near-infrared Light Curves and Comparison to Kilonova Models

“…Rapid optical follow-up by our Dark Energy Camera (DECam) program (Flaugher et al 2015), starting just 11.4 hr after the GW trigger, led to the discovery of an associated optical counterpart in the nearby ( » d 39.5 Mpc; Freedman et al 2001) galaxy NGC 4993 (Allam et al 2017;Soares-Santos et al 2017). This optical source was independently discovered by several groups (Abbott et al 2017b), and first announced as SSS17a by Coulter et al (2017aCoulter et al ( , 2017b. The source has also been independently named DLT17ck Yang et al 2017) and AT2017gfo.…”

On the High-Energy Neutrino Emission from Active Galactic Nuclei

“…We observe UHECR particles, and two scenarios are viable to explain them, with probably both realized in nature [52]: one is based on the relativistic jets and their shock waves in radio galaxies (e.g., [46]), and the other on Gamma Ray Bursts (GRBs) and their relativistic jets. Both sites of origin may involve mergers of black holes or neutron stars [51,53], or the ab initio formation of black holes. In a series of papers by Mannheim, Falcke and Markoff (e.g., [43,54,55]) it has been shown that at a distance of order 10 3.5 to 10 5 Schwarzschild radii from a central black hole a reconfinement shock system occurs, starting the routine jet flow (e.g., [56,57]).…”

Ondas gravitacionais

“…Desde então, mais 4 eventos similares foram detetados, na verdade, em frequências audíveis para um humano [7][8][9] . Em agosto do presente ano foi anunciada a observação de ondas originadas na fusão de duas estrelas de neutrões, e, simultaneamente, também a observação de radiação gama e no visível 10,11 .…”