The discovery of the electromagnetic counterpart of GW170817: kilonova AT 2017gfo/DLT17ck

TL;DR

This paper reports the discovery of the optical kilonova counterpart to GW170817, confirming the link between neutron star mergers, short gamma-ray bursts, and kilonovae, marking a new era in multi-messenger astronomy.

Contribution

First detection of an optical kilonova associated with a gravitational wave event, providing direct observational evidence of neutron star mergers as kilonova sources.

Findings

Confirmed the optical counterpart of GW170817 as a kilonova

Provided detailed photometric and spectroscopic evolution data

Supported kilonova models predicting rapid optical evolution

Abstract

During the second observing run of the Laser Interferometer gravitational- wave Observatory (LIGO) and Virgo Interferometer, a gravitational-wave signal consistent with a binary neutron star coalescence was detected on 2017 August 17th (GW170817), quickly followed by a coincident short gamma-ray burst trigger by the Fermi satellite. The Distance Less Than 40 (DLT40) Mpc supernova search performed pointed follow-up observations of a sample of galaxies regularly monitored by the survey which fell within the combined LIGO+Virgo localization region, and the larger Fermi gamma ray burst error box. Here we report the discovery of a new optical transient (DLT17ck, also known as SSS17a; it has also been registered as AT 2017gfo) spatially and temporally coincident with GW170817. The photometric and spectroscopic evolution of DLT17ck are unique, with an absolute peak magnitude of Mr = -15.8 \pm 0.1 and an r-band decline rate of 1.1mag/d. This fast evolution is generically consistent with kilonova models, which have been predicted as the optical counterpart to binary neutron star coalescences. Analysis of archival DLT40 data do not show any sign of transient activity at the location of DLT17ck down to r~19 mag in the time period between 8 months and 21 days prior to GW170817. This discovery represents the beginning of a new era for multi-messenger astronomy opening a new path to study and understand binary neutron star coalescences, short gamma-ray bursts and their optical counterparts.