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The binary neutron-star merger GW170817 1 was accompanied by radiation across the electromagnetic spectrum 2 and localized 2 to the galaxy NGC 4993 at a distance 3 of about 41 megaparsecs from Earth. The radio and X-ray afterglows of GW170817 exhibited delayed onset 4 – 7 , a gradual increase 8 in the emission with time (proportional to t 0.8 ) to a peak about 150 days after the merger event 9 , followed by a relatively rapid decline 9 , 10 . So far, various models have been proposed to explain the afterglow emission, including a choked-jet cocoon 4 , 8 , 11 – 13 and a successful-jet cocoon 4 , 8 , 11 – 18 (also called a structured jet). However, the observational data have remained inconclusive 10 , 15 , 19 , 20 as to whether GW170817 launched a successful relativistic jet. Here we report radio observations using very long-baseline interferometry. We find that the compact radio source associated with GW170817 exhibits superluminal apparent motion between 75 days and 230 days after the merger event. This measurement breaks the degeneracy between the choked- and successful-jet cocoon models and indicates that, although the early-time radio emission was powered by a wide-angle outflow 8 (a cocoon), the late-time emission was most probably dominated by an energetic and narrowly collimated jet (with an opening angle of less than five degrees) and observed from a viewing angle of about 20 degrees. The imaging of a collimated relativistic outflow emerging from GW170817 adds substantial weight to the evidence linking binary neutron-star mergers and short γ-ray bursts. Emission from the radio counterpart of the gravitation-wave event GW170817 was powered by a wide-angle outflow at early times, but probably dominated by a narrowly collimated jet at later times.

Gravitational waves have been detected from a binary neutron star merger event, GW170817. The detection of electromagnetic radiation from the same source has shown that the merger occurred in the outskirts of the galaxy NGC 4993, at a distance of 40 megaparsecs from Earth. We report the detection of a counterpart radio source that appears 16 days after the event, allowing us to diagnose the energetics and environment of the merger. The observed radio emission can be explained by either a collimated ultrarelativistic jet, viewed off-axis, or a cocoon of mildly relativistic ejecta. Within 100 days of the merger, the radio light curves will enable observers to distinguish between these models, and the angular velocity and geometry of the debris will be directly measurable by very long baseline interferometry.

The observed electromagnetic emission from GW170817 suggests that a ‘cocoon’ of mildly relativistic material was released as a jet transferred its energy to the neutron-rich dynamical ejecta from the merger. Radio waves reveal wide-angle outflow from merging stars On 17 August 2017, the detection of a gravitational-wave signature of merging neutron stars preceded that of a weak, short γ-ray burst. The source was quickly localized to the galaxy NGC 4993, and a range of telescopes measuring different parts of the electromagnetic spectrum followed the source, which was fading at most wavelengths. The radio emission, however, has continued to increase. Kunal Mooley and colleagues report continuing radio observations that are inconsistent with the off-axis relativistic jet that was initially believed to explain the optical, X-ray and γ-ray data. Instead, the radio data are best explained by a mildly relativistic wide-angle outflow. GW170817 was the first gravitational-wave detection of a binary neutron-star merger 1 . It was accompanied by radiation across the electromagnetic spectrum and localized 2 to the galaxy NGC 4993 at a distance of 40 megaparsecs. It has been proposed that the observed γ-ray, X-ray and radio emission is due to an ultra-relativistic jet being launched during the merger (and successfully breaking out of the surrounding material), directed away from our line of sight (off-axis) 3 , 4 , 5 , 6 . The presence of such a jet is predicted from models that posit neutron-star mergers as the drivers of short hard-γ-ray bursts 7 , 8 . Here we report that the radio light curve of GW170817 has no direct signature of the afterglow of an off-axis jet. Although we cannot completely rule out the existence of a jet directed away from the line of sight, the observed γ-ray emission could not have originated from such a jet. Instead, the radio data require the existence of a mildly relativistic wide-angle outflow moving towards us. This outflow could be the high-velocity tail of the neutron-rich material that was ejected dynamically during the merger, or a cocoon of material that breaks out when a jet launched during the merger transfers its energy to the dynamical ejecta. Because the cocoon model explains the radio light curve of GW170817, as well as the γ-ray and X-ray emission (and possibly also the ultraviolet and optical emission) 9 , 10 , 11 , 12 , 13 , 14 , 15 , it is the model that is most consistent with the observational data. Cocoons may be a ubiquitous phenomenon produced in neutron-star mergers, giving rise to a hitherto unidentified population of radio, ultraviolet, X-ray and γ-ray transients in the local Universe.

Radio observations of tidal disruption events (TDEs)—when a star is tidally disrupted by a supermassive black hole (SMBH)—provide a unique laboratory for studying outflows in the vicinity of SMBHs and their connection to accretion onto the supermassive black hole. Radio emission has been detected in only a handful of TDEs so far. Here we report the detection of delayed radio flares from an optically discovered TDE. Our prompt radio observations of the TDE ASASSN-15oi showed no radio emission until the detection of a flare six months later, followed by a second and brighter flare years later. We find that the standard scenario, in which an outflow is launched briefly after the stellar disruption, is unable to explain the combined temporal and spectral properties of the delayed flare. We suggest that the flare is due to the delayed ejection of an outflow, perhaps following a transition in accretion states. Our discovery motivates observations of TDEs at various timescales and highlights a need for new models. A delayed radio flare six months after an optically discovered tidal disruption event, followed by a second and brighter flare, years later, may potentially be due to the delayed ejection of an outflow following a transition in accretion states.

Measurement of polarized light provides a direct probe of magnetic fields in collimated outflows (jets) of relativistic plasma from accreting stellar-mass black holes at cosmological distances. These outflows power brief and intense flashes of prompt gamma-rays known as Gamma Ray Bursts (GRBs), followed by longer-lived afterglow radiation detected across the electromagnetic spectrum. Rapid-response polarimetric observations of newly discovered GRBs have probed the initial afterglow phase. Linear polarization degrees as high as Π∼30% are detected minutes after the end of the prompt GRB emission, consistent with a stable, globally ordered magnetic field permeating the jet at large distances from the central source. In contrast, optical and gamma-ray observations during the prompt phase led to discordant and often controversial results, and no definitive conclusions on the origin of the prompt radiation or the configuration of the magnetic field could be derived. Here we report the detection of linear polarization of a prompt optical flash that accompanied the extremely energetic and long-lived prompt gamma-ray emission from GRB 160625B. Our measurements probe the structure of the magnetic field at an early stage of the GRB jet, closer to the central source, and show that the prompt GRB phase is produced via fast cooling synchrotron radiation in a large-scale magnetic field advected from the central black hole and distorted from dissipation processes within the jet.

Anthropogenic changes, such as land use, are the main drivers causing climate change and biodiversity loss, with hundreds of thousands of species lacking sufficient habitats for their populations to persist and likely to go extinct within decades. Endemic species are more susceptible to habitat changes and are at the forefront of the biodiversity crisis. We used species distribution models to generate a relative habitat suitability map and identified the habitat requirements of the critically endangered and endemic Be'er Sheva fringe‐fingered lizard (Acanthodactylus beershebensis). The model showed that the species' suitable habitats are associated with arid loess plains characterized by scattered, low vegetation cover, primarily on north‐facing aspects, suggesting that these species‐specific habitat requirements limit its distribution. The size of the potentially suitable area within the species' historical range is 1350.73 km2. However, anthropogenic changes decreased the remaining suitable habitat to 995.04 km2. Most of this area is unprotected and at risk of further adverse anthropogenic effects. Only 91.72 km2 of this area is protected by the Israel Nature and Parks Authority, and 587.11 km2 may be considered indirectly protected because it is within military firing zones. Our study is the first attempt to map the remaining suitable habitat of A. beershebensis based on the results of a species distribution model. The results of this model can assist in prioritizing the protection of areas needed for the conservation of this critically endangered and endemic lizard species. We used species distribution models to map the distribution and habitat requirements of the endemic and critically endangered Be'er Sheva fringe‐fingered lizard (Acanthodactylus beershebensis). The size of the potentially suitable area within the species historical range is 1350.73 km2. However, anthropogenic changes shrunk the remaining suitable habitat to 995.04 km2. Only 91.72 km2 of this area is protected by the Israel Nature and Parks Authority, and 587.11 km2 may be considered indirectly protected because it is within military firing zones. Our study is the first attempt to map the remaining suitable habitat of the critically endangered lizard species A. beershebensis based on the results of a species distribution model.

A mass-loss event 40 days before the explosion of the type IIn supernova SN 2010mc has been detected; the outburst indicates that there is a causal relation between explosive mass-loss events seen in some massive stars before their explosion and the onset of the supernova explosion. Energetic mass loss precedes supernova explosion Various lines of evidence suggest that very massive stars experience extreme mass-loss episodes shortly before they explode as supernovae. This paper reports the observation of one such event: 40 days before the explosion of the type IIn supernova SN 2010mc its progenitor underwent an energetic outburst that released 0.01 solar masses of material at velocities of around 2,000 km per second.The luminosity and velocity of the outburst are consistent with the predictions of the wave-driven pulsation model of supernova explosions. Some observations suggest that very massive stars experience extreme mass-loss episodes shortly before they explode as supernovae 1 , 2 , 3 , 4 , as do several models 5 , 6 , 7 . Establishing a causal connection between these mass-loss episodes and the final explosion would provide a novel way to study pre-supernova massive-star evolution. Here we report observations of a mass-loss event detected 40 days before the explosion of the type IIn supernova SN 2010mc (also known as PTF 10tel). Our photometric and spectroscopic data suggest that this event is a result of an energetic outburst, radiating at least 6 × 10 47  erg of energy and releasing about 10 −2 solar masses of material at typical velocities of 2,000 km s −1 . The temporal proximity of the mass-loss outburst and the supernova explosion implies a causal connection between them. Moreover, we find that the outburst luminosity and velocity are consistent with the predictions of the wave-driven pulsation model 6 , and disfavour alternative suggestions 7 .

Some types of core-collapse supernovae are known to produce a neutron star (NS). A binary NS merger was recently detected from its gravitational wave emission, but it is unclear how such a tight binary system can be formed. De et al. discovered a core-collapse supernova with unusual properties, including the removal of the outer layers of the star before the explosion. They interpret this as the second supernova in an interacting binary system that already contains one NS. Because the explosion probably produced a second NS (rather than a black hole) in a tight orbit, it could be an example of how binary NS systems form. Science , this issue p. 201 An unusual core-collapse supernova appears to have formed a binary neutron star in a tight orbit. Compact neutron star binary systems are produced from binary massive stars through stellar evolution involving up to two supernova explosions. The final stages in the formation of these systems have not been directly observed. We report the discovery of iPTF 14gqr (SN 2014ft), a type Ic supernova with a fast-evolving light curve indicating an extremely low ejecta mass (≈0.2 solar masses) and low kinetic energy (≈2 × 10 50 ergs). Early photometry and spectroscopy reveal evidence of shock cooling of an extended helium-rich envelope, likely ejected in an intense pre-explosion mass-loss episode of the progenitor. Taken together, we interpret iPTF 14gqr as evidence for ultra-stripped supernovae that form neutron stars in compact binary systems.

The early evolution of a supernova (SN) can reveal information about the environment and the progenitor star. When a star explodes in vacuum, the first photons to escape from its surface appear as a brief, hours-long shock-breakout flare 1 , 2 , followed by a cooling phase of emission. However, for stars exploding within a distribution of dense, optically thick circumstellar material (CSM), the first photons escape from the material beyond the stellar edge and the duration of the initial flare can extend to several days, during which the escaping emission indicates photospheric heating 3 . Early serendipitous observations 2 , 4 that lacked ultraviolet (UV) data were unable to determine whether the early emission is heating or cooling and hence the nature of the early explosion event. Here we report UV spectra of the nearby SN 2023ixf in the galaxy Messier 101 (M101). Using the UV data as well as a comprehensive set of further multiwavelength observations, we temporally resolve the emergence of the explosion shock from a thick medium heated by the SN emission. We derive a reliable bolometric light curve that indicates that the shock breaks out from a dense layer with a radius substantially larger than typical supergiants. Using ultraviolet data as well as a comprehensive set of further multiwavelength observations of the supernova 2023ixf, a reliable bolometric light curve is derived that indicates the heating nature of the early emission.

The detection of strong emission lines in an early-time spectrum of type IIb supernova SN 2013cu reveals Wolf–Rayet-like wind signatures, suggesting that the supernova’s progenitor may have been a Wolf–Rayet star with a wind dominated by helium and nitrogen, with traces of hydrogen. Progression from Wolf-Rayet star to type IIb supernova Wolf–Rayet stars, massive objects stripped of their outer hydrogen-rich envelope, are one of a number of candidates as supernova progenitors for type IIb, Ib and Ic explosions. This paper reports the detection of strong emission lines in early spectra — just 15 hours after the blast — from the type IIb supernova SN 2013cu that are consistent with a Wolf–Rayet star as progenitor. The extent of this dense supernova wind implies possible increased mass loss from the progenitor shortly before the explosion, consistent with recent theoretical predictions. An accompanying News & Views article suggests that the new findings are the most direct evidence yet that these massive stars do end their lives as supernovae. The explosive fate of massive Wolf–Rayet stars 1 (WRSs) is a key open question in stellar physics. An appealing option is that hydrogen-deficient WRSs are the progenitors of some hydrogen-poor supernova explosions of types IIb, Ib and Ic (ref. 2 ). A blue object, having luminosity and colours consistent with those of some WRSs, has recently been identified in pre-explosion images at the location of a supernova of type Ib (ref. 3 ), but has not yet been conclusively determined to have been the progenitor. Similar work has so far only resulted in non-detections 4 . Comparison of early photometric observations of type Ic supernovae with theoretical models suggests that the progenitor stars had radii of less than 10 12  centimetres, as expected for some WRSs 5 . The signature of WRSs, their emission line spectra, cannot be probed by such studies. Here we report the detection of strong emission lines in a spectrum of type IIb supernova 2013cu (iPTF13ast) obtained approximately 15.5 hours after explosion (by ‘flash spectroscopy’, which captures the effects of the supernova explosion shock breakout flash on material surrounding the progenitor star). We identify Wolf–Rayet-like wind signatures, suggesting a progenitor of the WN(h) subclass (those WRSs with winds dominated by helium and nitrogen, with traces of hydrogen). The extent of this dense wind may indicate increased mass loss from the progenitor shortly before its explosion, consistent with recent theoretical predictions 6 .