The Emergence of the Infrared Transient VVV-WIT-06*

Abstract

<p><span>We report the discovery of an enigmatic large-amplitude (&Delta;<em>Ks &gt; </em>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. = &minus;39:06:26.45 (J2000), corresponding to Galactic coordinates <em>l</em> = 347.14539, <em>b</em> = 0.88522. It exhibits a clear eruption, peaking at <em>Ks</em> = 9 mag during 2013 July and fading to <em>Ks</em> ~ 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^&minus;1). We estimate a total extinction of <em>&Alpha;_v</em> = 10 15 &ndash; mag in the surrounding field, and no progenitor was observed in <em>ZYJHKs</em> images obtained during 2010&ndash;2012 (down to <em>K_s</em> &gt; 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.</span></p>