Details

Autor(en) / Beteiligte

• Pian, E.
• D’Avanzo, P.
• Benetti, S.
• Branchesi, M.
• Brocato, E.
• Campana, S.
• Cappellaro, E.
• Covino, S.
• D’Elia, V.
• Fynbo, J. P. U.
• Getman, F.
• Ghirlanda, G.
• Ghisellini, G.
• Grado, A.
• Greco, G.
• Hjorth, J.
• Kouveliotou, C.
• Levan, A.
• Limatola, L.
• Malesani, D.
• Mazzali, P. A.
• Melandri, A.
• Møller, P.
• Nicastro, L.
• Palazzi, E.
• Piranomonte, S.
• Rossi, A.
• Salafia, O. S.
• Selsing, J.
• Stratta, G.
• Tanaka, M.
• Tanvir, N. R.
• Tomasella, L.
• Watson, D.
• Yang, S.
• Amati, L.
• Antonelli, L. A.
• Ascenzi, S.
• Bernardini, M. G.
• Boër, M.
• Bufano, F.
• Bulgarelli, A.
• Capaccioli, M.
• Casella, P.
• Castro-Tirado, A. J.
• Chassande-Mottin, E.
• Ciolfi, R.
• Copperwheat, C. M.
• Dadina, M.
• De Cesare, G.
• Di Paola, A.
• Fan, Y. Z.
• Gendre, B.
• Giuffrida, G.
• Giunta, A.
• Hunt, L. K.
• Israel, G. L.
• Jin, Z.-P.
• Kasliwal, M. M.
• Klose, S.
• Lisi, M.
• Longo, F.
• Maiorano, E.
• Mapelli, M.
• Masetti, N.
• Nava, L.
• Patricelli, B.
• Perley, D.
• Pescalli, A.
• Piran, T.
• Possenti, A.
• Pulone, L.
• Razzano, M.
• Salvaterra, R.
• Schipani, P.
• Spera, M.
• Stamerra, A.
• Stella, L.
• Tagliaferri, G.
• Testa, V.
• Troja, E.
• Turatto, M.
• Vergani, S. D.
• Vergani, D.

Titel

Spectroscopic identification of r-process nucleosynthesis in a double neutron-star merger

Ist Teil von

• Nature (London), 2017-11, Vol.551 (7678), p.67-70

Ort / Verlag

London: Nature Publishing Group UK

Erscheinungsjahr

2017

Beschreibungen/Notizen

• Observations of the transient associated with the gravitational-wave event GW170817 and γ-ray burst GRB 170817A reveal a bright kilonova with fast-moving ejecta, including lanthanides synthesized by rapid neutron capture. When neutron stars collide Merging neutron stars are potential sources of gravitational waves and have long been predicted to produce jets of material as part of a low-luminosity transient known as a 'kilonova'. There is growing evidence that neutron-star mergers also give rise to short, hard gamma-ray bursts. A group of papers in this issue report observations of a transient associated with the gravitational-wave event GW170817—a signature of two neutron stars merging and a gamma-ray flash—that was detected in August 2017. The observed gamma-ray, X-ray, optical and infrared radiation signatures support the predictions of an outflow of matter from double neutron-star mergers and present a clear origin for gamma-ray bursts. Previous predictions differ over whether the jet material would combine to form light or heavy elements. These papers now show that the early part of the outflow was associated with lighter elements whereas the later observations can be explained by heavier elements, the origins of which have been uncertain. However, one paper (by Stephen Smartt and colleagues) argues that only light elements are needed for the entire event. Additionally, Eleonora Troja and colleagues report X-ray observations and radio emissions that suggest that the 'kilonova' jet was observed off-axis, which could explain why gamma-ray-burst detections are seen as dim. The merger of two neutron stars is predicted to give rise to three major detectable phenomena: a short burst of γ-rays, a gravitational-wave signal, and a transient optical–near-infrared source powered by the synthesis of large amounts of very heavy elements via rapid neutron capture (the r-process) 1 , 2 , 3 . Such transients, named ‘macronovae’ or ‘kilonovae’ 4 , 5 , 6 , 7 , are believed to be centres of production of rare elements such as gold and platinum 8 . The most compelling evidence so far for a kilonova was a very faint near-infrared rebrightening in the afterglow of a short γ-ray burst 9 , 10 at redshift z  = 0.356, although findings indicating bluer events have been reported 11 . Here we report the spectral identification and describe the physical properties of a bright kilonova associated with the gravitational-wave source 12 GW170817 and γ-ray burst 13 , 14 GRB 170817A associated with a galaxy at a distance of 40 megaparsecs from Earth. Using a series of spectra from ground-based observatories covering the wavelength range from the ultraviolet to the near-infrared, we find that the kilonova is characterized by rapidly expanding ejecta with spectral features similar to those predicted by current models 15 , 16 . The ejecta is optically thick early on, with a velocity of about 0.2 times light speed, and reaches a radius of about 50 astronomical units in only 1.5 days. As the ejecta expands, broad absorption-like lines appear on the spectral continuum, indicating atomic species produced by nucleosynthesis that occurs in the post-merger fast-moving dynamical ejecta and in two slower (0.05 times light speed) wind regions. Comparison with spectral models suggests that the merger ejected 0.03 to 0.05 solar masses of material, including high-opacity lanthanides.