Minniti, D.D.MinnitiSaito, R. K.R. K.SaitoForster, F.F.ForsterPignata, G.G.PignataIvanov, V. D.V. D.IvanovLucas, P. W.P. W.LucasBeamin, J. C.J. C.BeaminBorissova, J.J.BorissovaCatelan, M.M.CatelanGonzalez, O. A.O. A.GonzalezHempel, M.M.HempelHsiao, E.E.HsiaoKurtev, R.R.KurtevMajaess, D.D.MajaessMASETTI, NICOLANICOLAMASETTIMorrell, N. I.N. I.MorrellPhillips, M. M.M. M.PhillipsPullen, J. B.J. B.PullenRejkuba, M.M.RejkubaSmith, L.L.SmithSurot, F.F.SurotValenti, E.E.ValentiZoccali, M.M.Zoccali2020-08-062020-08-0620172041-8205http://hdl.handle.net/20.500.12386/26701We report the discovery of an enigmatic large-amplitude ({{∆ }}{Ks}> 10.5 mag) transient event in near-IR data obtained by the VISTA Variables in the Via Lactea (VVV) ESO Public Survey. The object (designated VVV-WIT-06) is located at R.A. = 17:07:18.917, decl. = -39:06:26.45 (J2000), corresponding to Galactic coordinates l = 347.14539, b = 0.88522. It exhibits a clear eruption, peaking at Ks = 9 mag during 2013 July and fading to {Ks}∼ 16.5 in 2017. Our late near-IR spectra show post-outburst emission lines, including some broad emission lines (upward of {FWHM}∼ 3000 km s<SUP>-1</SUP>). We estimate a total extinction of {A}<SUB>V</SUB>=10{--}15 mag in the surrounding field, and no progenitor was observed in ZYJHKs images obtained during 2010-2012 (down to {K}<SUB>s</SUB>> 18.5 mag). Subsequent deep near-IR imaging and spectroscopy, in concert with the available multiband photometry, indicate that VVV-WIT-06 may be either: (I) the closest Type I SN observed in about 400 years, (II) an exotic high-amplitude nova that would extend the known realm of such objects, or (III) a stellar merger. In all of these cases, VVV-WIT-06 is a fascinating and curious astrophysical target under any of the scenarios considered. <P />Based on observations taken within the ESO programmes 179.B-2002 and 298.D-5048, and on observations carried out at the Magellan Telescope at LCO.STAMPAenArticle10.3847/2041-8213/aa93742-s2.0-85034453576000414455200002https://iopscience.iop.org/article/10.3847/2041-8213/aa93742017ApJ...849L..23MFIS/05 - ASTRONOMIA E ASTROFISICAScienze Fisiche Settori ERC (ERC) di riferimento::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation::PE9_11 Relativistic astrophysics