We report the discovery of an X-ray/UV stellar flare from the source LMC 335 , captured by XMM-Newton in the field of the Large Magellanic Cloud .
The flare event was recorded continuously in X-ray for its first 10 hours from the precursor to the late decay phases .
The observed fluxes increased by more than two orders of magnitude at its peak in X-ray and at least one in the UV as compared to quiescence .
The peak 0.1 - 7.0 keV X-ray flux is derived from the two-temperature APEC model to be \sim ( 8.4 \pm 0.6 ) \times 10 ^ { -12 } erg cm ^ { -2 } s ^ { -1 } .
Combining astrometric information from multiple X-ray observations in the quiescent and flare states , we identify the NIR counterpart of LMC 335 as the 2MASS source J05414534 - 6921512 .
The NIR color relations and spectroscopic parallax characterize the source as a Galactic K7 - M4 dwarf at a foreground distance of ( 100 - 264 ) pc , implying a total energy output of the entire event of \sim ( 0.4 - 2.9 ) \times 10 ^ { 35 } erg .
This report comprises detailed analyses of this late K / early M dwarf flare event that has the longest time coverage yet reported in the literature .
The flare decay can be modeled with two exponential components with timescales of \sim 28 min and \sim 4 hours , with a single component decay firmly ruled out .
The X-ray spectra during flare can be described by two components , a dominant high temperature component of \sim 40 - 60 MK and a low temperature component of \sim 10 MK , with a flare loop length of about 1.1 - 1.3 stellar radius .