MELANDRI, AndreaAndreaMELANDRIROSSI, AndreaAndreaROSSIBENETTI, StefanoStefanoBENETTID'Elia, V.V.D'EliaPIRANOMONTE, SilviaSilviaPIRANOMONTEPALAZZI, ELIANAELIANAPALAZZILevan, A. J.A. J.LevanBranchesi, M.M.BranchesiCastro-Tirado, A. J.A. J.Castro-TiradoD'AVANZO, PaoloPaoloD'AVANZOHu, Y. -D.Y. -D.HuRAIMONDO, GabriellaGabriellaRAIMONDOTanvir, N. R.N. R.TanvirTOMASELLA, LinaLinaTOMASELLAAMATI, LORENZOLORENZOAMATICAMPANA, SergioSergioCAMPANACARINI, RobertaRobertaCARINICOVINO, StefanoStefanoCOVINOCUSANO, FELICEFELICECUSANODADINA, MAUROMAURODADINADELLA VALLE, MassimoMassimoDELLA VALLEFan, X.X.FanGarnavich, P.P.GarnavichGRADO, ANIELLOANIELLOGRADOGreco, G.G.GrecoHjorth, J.J.HjorthLyman, J. D.J. D.LymanMASETTI, NICOLANICOLAMASETTIO'Brien, P.P.O'BrienPIAN, ElenaElenaPIANPerego, A.A.PeregoSALVATERRA, RubenRubenSALVATERRASTELLA, LuigiLuigiSTELLAStratta, G.G.StrattaYang, S.S.YangDI PAOLA, AndreaAndreaDI PAOLACaballero-García, M. D.M. D.Caballero-GarcíaFruchter, A. S.A. S.FruchterGiunta, A.A.GiuntaLongo, F.F.LongoPinamonti, MatteoMatteoPinamontiSokolov, V. V.V. V.SokolovTESTA, VincenzoVincenzoTESTAValeev, A. F.A. F.ValeevBROCATO, EnzoEnzoBROCATO2021-02-012021-02-0120190004-6361http://hdl.handle.net/20.500.12386/30138Aims: 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. <BR /> 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. <BR /> 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 E<SUB>p</SUB>-E<SUB>iso</SUB> 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. <P />Based on observations made with the following telescopes: Copernico, TNG (under programme A34TAC_24), GTC (under programmes GTCMULTIPLE2D-16B and GTCMULTIPLE2G-17A), LBT (under programme 2016_2017_19), and HST (under programme GO14270).Spectral data for this source shown on this paper are available on the Weizmann Interactive Supernova Data Repository (WISeREP, <A href="https://wiserep.weizmann.ac.il/">http://https://wiserep.weizmann.ac.il/</A>).STAMPAenArticle10.1051/0004-6361/2018338142-s2.0-85059963528000455271200001http://arxiv.org/abs/1807.03681v1https://www.aanda.org/articles/aa/full_html/2019/01/aa33814-18/aa33814-18.html2019A&A...621A..81MFIS/05 - ASTRONOMIA E ASTROFISICA