Photometry and spectroscopy of IRAS 18111-2257

Using data from the Palomar Gattini-IR survey, we identify a spatially and temporally coincident variable infrared (IR) source, IRAS-18111-2257, and classify it as a very-late-type (M7-M8), long-period (1502{+/-}24days), and luminous (MK~-9.9{+/-}0.2) O-rich Mira donor star located at a distance of ~14.6+2.9-2.3kpc.

Combining multicolor photometric data over the last ~25yr, we show that the IR counterpart underwent a recent (starting ~800days before the X-ray flare) enhanced mass-loss (reaching ~2.1x10^-5^M{sun} yr-1) episode, resulting in an expanding dust shell obscuring the underlying star. Multi- epoch follow-up observations from Swift, NICER, and NuSTAR reveal a ~200day long X-ray outburst reaching a peak luminosity of LX~2.5x1036erg/s, characterized by a heavily absorbed (NH~6x1022/cm^2^) X-ray spectrum consistent with an optically thick Comptonized plasma.