We present the analysis of the event OGLE-2017-BLG-1186 from the 2017 Spitzer microlensing campaign .
This event is remarkable because its source is photometrically variable .
We perform an asteroseismic analysis of the source star and find that it is an oscillating red giant with average timescale of \sim 9 days .
The asteroseismic analysis also provides us source properties including the source angular size ( \sim 27 ~ { } \mu { as } ) and distance ( \sim 11.5 kpc ) , which are essential for inferring the properties of the lens .
When fitting the light curve , we test the feasibility of Gaussian Processes ( GPs ) in handling the correlated noise caused by the variable source .
We find , in this event , that the GP model can not provide better constraints on the parameters of interest because of the worse estimation of blending fluxes compared to the traditional \chi ^ { 2 } minimization method .
We note that this event is the first microlensing system for which asteroseismology and GPs have been used to account for the variable source .
With both finite-source effect and microlens parallax measured , we find that the lens is likely a \sim 0.045 ~ { } M _ { \odot } brown dwarf at distance \sim 9.0 kpc , or a \sim 0.073 ~ { } M _ { \odot } ultracool dwarf at distance \sim 9.8 kpc .
Combining the estimated lens properties with a Bayesian analysis using a Galactic model , we find a \sim 35 \% probability for the lens to be a bulge object and \sim 65 \% to be a background disk object .