Abstract
Aims. The unusual transient ATLAS17aeu was serendipitously detected within the sky localisation of the gravitational wave trigger GW 170104. The importance of a possible association with gravitational waves coming from a binary black hole merger led to an extensive follow-up campaign, with the aim of assessing a possible connection with GW 170104. Methods. With several telescopes, we carried out both photometric and spectroscopic observations of ATLAS17aeu, for several epochs, between ∼3 and ∼230 days after the first detection. Results. We studied in detail the temporal and spectroscopic properties of ATLAS17aeu and its host galaxy. Although at low significance and not conclusive, we found similarities to the spectral features of a broad-line supernova superposed onto an otherwise typical long-GRB afterglow. Based on analysis of the optical light curve, spectrum, and host galaxy spectral energy distribution, we conclude that the redshift of the source is probably z ≃ 0.5 ± 0.2. Conclusions. While the redshift range we have determined is marginally compatible with that of the gravitational wave event, the presence of a supernova component and the consistency of this transient with the Ep–Eiso correlation support the conclusion that ATLAS17aeu was associated with the long gamma-ray burst GRB 170105A. This rules out the association of the GRB 170105A/ATLAS17aeu transient with the gravitational wave event GW 170104, which was due to a binary black hole merger.
Highlights
The first direct observation of gravitational waves by the Advanced LIGO interferometers came from the coalescence of a binary system of black holes (Abbott et al 2016a), opening the era of gravitational-wave astronomy
While the redshift range we have determined is marginally compatible with that of the gravitational wave event, the presence of a supernova component and the consistency of this transient with the Ep–Eiso correlation support the conclusion that ATLAS17aeu was associated with the long gamma-ray burst GRB 170105A. This rules out the association of the GRB 170105A/ATLAS17aeu transient with the gravitational wave event GW 170104, which was due to a binary black hole merger
We present optical observations of ATLAS17aeu transient and its possible host galaxy taken with the 1.8 m Asiago Copernico telescope, the 3.6 m Telescopio Nazionale Galileo (TNG), the 8.4 m Large Binocular telescope (LBT), the 10.4 m Gran Telescopio Canarias (GTC), and the Hubble Space Telescope (HST) over 230 days from the GRB 170105A trigger time
Summary
The first direct observation of gravitational waves by the Advanced LIGO interferometers came from the coalescence of a binary system of black holes (Abbott et al 2016a), opening the era of gravitational-wave astronomy. Gravitational-wave signals from binary systems of black holes were detected several times during the first and second run of observations of the advanced detectors (Abbott et al 2017a,b,c, 2016b). They provided us with information about their rate and mass distribution, and probed their formation and evolution. Considering all the multi-wavelength observations of ATLAS17aeu, Stalder et al (2017) concluded that the GRB 170105A is compatible with a classical long-GRB at redshift 1 z 2.9 and that ATLAS17aeu is statistically likely the associated afterglow They evaluated a small but non-negligible probability of association of ATLAS17aeu and the GW signal, which only a direct redshift measurement of the host galaxy of ATLAS17aeu could exclude. Magnitudes are in the AB system and errors are at a 1σ confidence level
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