GRAvitational Wave Inaf TeAm

This is the official web site of the GRAvitational Wave Inaf TeAm (GRAWITA).

The GRAWITA collaboration has the aim of carrying out follow-up observational campaigns in the radio, optical, NIR, X-ray, and gamma-ray bands of the gravitational wave (GW) detector triggers released by the ground-based interferometers network actually composed of the two Advanced LIGO (USA) and Advanced Virgo (Italy). Ground-based facilities used by GRAWITA include VLT Survey Telescope, Large Binocular Telescope, Telescopio Nazionale Galileo, Rapid Eye Mount Telescope, Asiago Observatory, Campo Imperatore Observatory, SRT. The exploitation of high-energy space-based facilities is also planned.

In this site, it is possible to find some information about us and about the observational facilities that are used to perform the search and characterization of GW events through follow-up observational campaigns triggered by the LIGO/Virgo Collaboration (LVC). Furthermore, some key scientific by-products project are also collected in this website since the search for transients in wide field images will provide the basis for a number of studies related to the Time Domain Astronomy.


The first EM counterpart of a GW observed by GRAWITA

On August 17th 2017 the first electromagnetic counterpart of a gravitational wave (GW) event originated by the coalescence of a double neutron star system (GW 170817, Abbott et al. 2017 Phys. Review) was finally observed. A world-wide extensive observing campaign was carried out to follow-up and study this source, with the forefront participation of our team. In particular, our unique VLT dataset provided the first compelling observational evidence for the existence of “kilonovae”, transient sources powered by radioactive decay of heavy elements resulting from the r–process nucleosynthesis of ejected neutron star matter.

GRAWITA team and international collaborators observed this source with an almost daily cadence during the period Aug 18 — Sep 02, 2017 (~ 0.5–15.5 days after the GW/GRB trigger). This follow-up campaign consisted of imaging (with REM, ESO-VST and ESO-VLT telescopes) and spectroscopic (with the VLT/X-shooter, covering the wavelength range 3200–24800 Angstrom, with VLT/FORS2, covering 3500–9000 Angstrom) observations at optical and NIR wavelengths.

Animated spectrum

Spectral evolution of the observed light from SSS17a as observed by VLT from 18th to 27th August 2017.

This dataset allow us to follow in detail the evolution of the spectral energy distribution of the AT2017gfo (labelled also SSS17a and DLT17ck) for a period of about two weeks. The first X-Shooter spectrum was obtained 1.5 day after the GW event and shows a blue and bright continuum and allows us to infer a high expansion velocity of the ejected material. In the following epochs the spectrum shape changes and the maximum moves toward the red wavelengths. Our spectra dataset presents rapid changes with time, which are not observed in typical supernova spectral evolution. On the contrary, the overall evolution of the spectra is well interpreted with the behavior expected for a kilonova, confirming the first unambiguous connection between this phenomenon and the gravitational wave signal.

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