M. Branchesi

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

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). Such transients, named ‘macronovae’ or ‘kilonovae’, are believed to be centres of production of rare elements such as gold and platinum. 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 at redshift z = 0.356, although findings indicating bluer events have been reported. Here we report the spectral identification and describe the physical properties of a bright kilonova associated with the gravitational-wave source GW170817 and γ-ray burst 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. 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.

A Precise Distance to the Host Galaxy of the Binary Neutron Star Merger GW170817 Using Surface Brightness Fluctuations

This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. We acknowledge funding from INAF project: Gravitational Wave Astronomy with the first detections of Advanced LIGO and Advanced VIRGO experiments (PI: E. Brocato). M.C., G.R., and J.P.B. acknowledge partial support from the PRIN INAF-2014 >EXCALIBURS: EXtragalactic distance scale CALIBration Using first-Rank Standard candles> project (PI: G. Clementini). The Berger Time-Domain Group at Harvard is supported in part by the NSF through grant AST-1714498, and by NASA through grants NNX15AE50G and NNX16AC22G. N.R.T. acknowledges support from STFC consolidated grant ST/N000757/1. P.D.A. and S.C. acknowledge support from ASI grant I/004/11/3. J.H. was supported by a VILLUM FONDEN Investigator grant (project number 16599). I.M. acknowledges STFC for partial support. We thank the anonymous referee for a clear and unequivocal report.

THESEUS: A key space mission concept for Multi-Messenger Astrophysics

Abstract The recent discovery of the electromagnetic counterpart of the gravitational wave source GW170817, has demonstrated the huge informative power of multi-messenger observations. During the next decade the nascent field of multi-messenger astronomy will mature significantly. Around 2030 and beyond, third generation ground-based gravitational wave detectors will be roughly ten times more sensitive than the current ones. At the same time, neutrino detectors currently upgrading to multi km 3 telescopes, will include a 10 km 3 facility in the Southern hemisphere. In this review, we describe the most promising sources of high frequency gravitational waves and neutrinos that will be detected in the next two decades. In this context, we show the important role of the Transient High Energy Sky and Early Universe Surveyor (THESEUS), a mission concept accepted by ESA for phase A study and proposed by a large international collaboration in response to the call for the Cosmic Vision Programme M5 missions. THESEUS aims at providing a substantial advancement in early Universe science as well as in multi–messenger and time–domain astrophysics, operating in strong synergy with future gravitational wave and neutrino detectors as well as major ground- and space-based telescopes. This review is an extension of the THESEUS white paper (Amati et al., 2017), also in light of the discovery of GW170817/GRB170817A that was announced on October 16th, 2017.

GRAWITA: VLT Survey Telescope observations of the gravitational wave sources GW150914 and GW151226

We report the results of deep optical follow-up surveys of the first two gravitational-wave sources, GW150914 and GW151226, done by the GRAvitational Wave Inaf TeAm Collaboration (GRAWITA). The VLT Survey Telescope (VST) responded promptly to the gravitational-wave alerts sent by the LIGO and Virgo Collaborations, monitoring a region of

GW150914: First search for the electromagnetic counterpart of a gravitational-wave event by the TOROS collaboration

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The evolution of the X-ray afterglow emission of GW 170817/ GRB 170817A in XMM-Newton observations

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The e-ASTROGAM gamma-ray space observatory for the multimessenger astronomy of the 2030s

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Singular Spectrum Analysis for Astronomical Time Series: Constructing a Parsimonious Hypothesis Test

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Electromagnetic follow-up of gravitational wave candidates: perspectives in INAF

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Short gamma-ray bursts at the dawn of the gravitational wave era

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