GRAWITA – GRAvitational Wave Inaf TeAm

AT2017gfo

The first EM counterpart of a GW observed by GRAWITA team!

 

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 LINK) 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 behaviour expected for a kilonova, confirming the first unambiguous connection between this phenomenon and the gravitational wave signal.

October 16th, 2017


GRAWITA Group

This is the official GRAWITA (GRAvitational Wave Inaf TeAm) web page. Starting from mid September 2015, the Gravitational Waves detector advanced-LIGO became operative. In autumn 2016, another GW detector, advanced-Virgo will start its science runs. Our team GRAWITA is carrying out follow-up observational campaigns in the optical/NIR bands of the GW trigger observable with the VST, VLT, LBT, TNG, REM ground-based facilities.

The Memorandum of Understanding (MOU), signed in May 2014, establishes a collaborative effort among the Laser Inter- ferometerGravitational-Wave Observatory (LIGO) and LIGO Scientific Collaboration, the European Gravitational Observatory and Virgo Collaboration (EGO/Virgo), and Project of Istituto Nazionale di Astrofisica (INAF) in order to participate in a program to perform follow-up observations of gravitational wave candidate events with the sharing of proprietary information.

Since May 2015, an INAF team is working to make possible a prompt observational campaign to GW alert from LIGO/VIRGO collaboration (LVC). In fact, the MoU provide the possibility of accessing to key information (time and position in the sky) of all the gravitational waves (GW) detection from LVC. To this aim, GRAWITA has several actived proposals to LBT, TNG, VLT, ASIAGO, SRT etc. To improve the chances of accessing to observational time, it has been build up an extended network of international collaborations.

In this site, it is possible to find some information about the observational facilities that can be used to perform the search, characterization and follow-up observation just after the trigger on GW detection provided by LVC. Further, some key scientific by-products project are also collected in this website. This make clear that there will be also a guaranteed outcome of this research: in fact the search for transients in wide field images will provide the basis for a number of studies related to the Time Domain Astronomy.

Please email us at gw-em-followup@oa-roma.inaf.it, or contact enzo.brocato@oa-roma.inaf.it if you have any questions.

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