VVV-WIT-08: the giant star that blinked

We report the serendipitous discovery of a late-type giant star that exhibited smooth, eclipse-like drop in flux to depth 97 per cent. Minimum occurred April 2012 and total event duration was few hundred days. Light curves V, I K$_s$ from Optical Gravitational Lensing Experiment VISTA Variables Via Lactea surveys show remarkably achromatic event. During 17 years observational coverage this source only one such detected. The physical properties itself appear somewhat unusual, which may ultimately provide clue towards nature system. By modelling as an occultation by object is elliptical projection with uniform transparency, we place limits on its size velocity. find unlikely be due chance alignment foreground object. consider number possible candidates for occulter, must optically thick possess radius or thickness excess 0.25 au. None are completely satisfactory matches all data. duration, relative achromaticity dip mark out exceptionally unusual event, whose secret has still not been fully revealed. two further VVV survey suggest these systems, previously known examples, point broad class long period eclipsing binaries wherein occulted circumsecondary disc.