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.

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Soft gamma repeaters are high-energy transient sources associated with neutron stars in young supernova remnants 1 . They emit sporadic, short (∼ 0.1 s) bursts with soft energy spectra during periods of intense activity. The event of March 5, 1979 was the most intense and the only clearly periodic one to date 2,7 . Here we report on an even more intense burst on August 27, 1998, from a different soft gamma repeater, which displayed a hard energy spectrum at its peak, and was followed by a ∼ 300 s long tail with a soft energy spectrum and a dramatic 5.16 s period. Its peak and time integrated energy fluxes at Earth are the largest yet observed from any cosmic source. This event was probably initiated by a massive disruption of the neutron star crust, followed by an outflow of energetic particles rotating with the period of the star. Comparison of these two bursts supports the idea that magnetic energy plays an important role, and that such giant flares, while rare, are not unique, and may occur at any time in the neutron star's activity cycle.Four soft gamma repeaters (SGRs) are known. All appear to be associated with radio supernova remnants, indicating that they are young 4 (<20,000 y). SGRs are probably strongly magnetized neutron stars ('magnetars' 5 ), in which, unlike the radio pulsars, the magnetic energy dominates the rotational energy. SGR0525-66 produced both the unusual, energetic and periodic burst of March 5 1979 6,7,8 and a series of subsequent, much smaller bursts 9,10 . It lies towards the N49 supernova remnant in the Large Magellanic Cloud 11,12 . A quiescent soft X-ray source has been identified which may be the neutron star 13 . SGR1900+14, first detected in 1979, was, until recently, the least prolific SGR 14,15 , hindering attempts to locate it precisely. Several lines of evidence suggested that it was associated with the galactic supernova remnant G42.8+0.6 16 and a quiescent soft X-ray source 17 . This possible association was strengthened by a source location obtained with the network synthesis method 18 , and more recently by triangulation 19,20,21 , although since this X-ray source lies outside the remnant, the connection between the two could still be considered to be unresolved.

Abstract. 'The Konus-W experiment to be flown on board the GGS-Wind spacecraft is designed to observe gamma-ray bursts and solar flares with moderate spectral and high time resolution. Two large scintillators are used to provide omnidirectional sensitivity. The primary scientific objectives are the study of the continuum energy spectra and spectral features of these events in the energy range of 10 keV to 10 MeV, as well as their time histories in soft, medium, and hard energy bands, with a time resolution to 2 ms.