  Strong accretion outbursts onto protostars are associated with emission
dominated by a viscously heated disk, which is characterized by high
luminosities. We report the discovery and characterization of a strong mid-IR
(3.4, 4.6 $\mu$m) outburst in the embedded protostar SSTgbs J21470601+4739394
(hereafter SSTgbsJ214706). SSTgbsJ214706 has steadily brightened in the
mid-infrared by $\sim2$ magnitudes over the past decade, as observed by
NEOWISE. Follow-up investigations with the Gemini near-IR spectrograph reveal
that SSTgbsJ214706 is a binary system with a spatially extended outflow. The
outburst is occurring on the more embedded southeast (SE) component, which
dominates the mid- and far-infrared emission from the source. The outbursting
component exhibits a spectrum consistent with an FU Ori-type outburst,
including the presence of enhanced absorption observed in the molecular bands
of CO. The luminosity of the SE component is estimated to be $\sim 0.23\,$
L$_\odot$ before the outburst and $\sim 0.95\,$ L$_\odot$ during the outburst,
which is 1 to 2 orders of magnitude fainter than bonafide FU Ori outbursts. We
interpret this eruption as an FU Ori-type outburst, although the possibility of
brightening following an extinction episode cannot be ruled out. We discuss the
implications and potential explanations for such a low-luminosity eruption.
