We report the serendipitous discovery of a giant mid-infrared (MIR) outburst
from a previously unknown source near a star-forming region in the
constellation Monoceros. The source gradually brightened by a factor of 5 from
2014 to 2016 before an abrupt rise by a factor of more than 100 in 2017. A
total amplitude increase of >500 at 4.5 microns has since faded by a factor of
about 10. Prior to the outburst, it was only detected at wavelengths longer
than 1.8 microns in UKIDSS, Spitzer, and Herschel with a spectral energy
distribution of a Class I Young Stellar Object (YSO). It has not been detected
in recent optical surveys, suggesting that it is deeply embedded. With a
minimum distance of 3.5 kpc, the source has a bolometric luminosity of at least
9 Lββ in the quiescent state and 400 Lββ at the peak of the
eruption. The maximum accretion rate is estimated to be at least a few
10β5Mββ yearβ1. It shares several common properties with
another eruptive event, WISE~J142238.82-611553.7: exceptionally large
amplitude, featureless near-infrared spectrum with the exception of H_2 lines,
intermediate eruption duration, an embedded Class I YSO, and a low radiative
temperature (<600-700 K) in outburst. We interpret that the radiation from the
inner accretion disk and young star is obscured and reprocessed by either an
inflated outer disk or thick dusty outflow on scales > 6.5 AU during the
outburst.Comment: 15 pages, 7 figures, accepted to Ap