The Emergence of the Infrared transient VVV-WIT-06

Minniti, Dante, Saito, Roberto K., Forster, F., Pignata, G., Ivanov, Valentin D., Lucas, Philip, Beamin, J.C., Borissova, Jura, Catelan, Marcio, Gonzalez, Oscar A., Hempel, Maren, Hsiao, E, Kurtev, Radostin, Majaess, Daniel, Masetti, N., Morrell, N.I., Phillips, M.M., Pullen, J. B., Rejkuba, M., Smith, L.C., Surot, F., Valenti, Elena and Zoccali, Manuela (2017) The Emergence of the Infrared transient VVV-WIT-06. Astrophysical Journal Letters, 849 (2): L23. ISSN 2041-8205

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We report the discovery of an enigmatic large-amplitude (ΔKs> 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 k/s). We estimate a total extinction of A_V=10--15 mag in the surrounding field, and no progenitor was observed in ZYJHKs images obtained during 2010-2012 (down to Ks> 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.