in the Galactic bulge [@holtzman98]. Because of high stellar density and large uncertainty in blending flux, we cannot unambiguously attribute the blending flux to the lens.

The intrinsic color ($(V-I)_{\rm RC,0} = 1.06~{\rm mag}$) and brightness ($I_{\rm RC,0} = 14.47~{\rm mag}$) of the red clump were taken from @bensby11 and @nataf13b, respectively. By combining these with the measured color and brightness of the red clump in the vicinity of the event, we obtained the reddening and extinction of $E(V-I) = 1.70~{\rm mag}$ and $A_I = 1.96~{\rm mag}$. The dereddened color and brightness of the source star were measured using microlensing model: $(V-I)_0 = 1.12~{\rm mag}$ and $I_0 = 15.66~{\rm mag}$. Using the relations by @bessell88, we obtain the source color $(V-K)_0 = 2.60~{\rm mag}$, which correlates well with the source size [@kervella04giant]. The measured angular size of the source is $\theta_* = 6.3 \pm 0.3 {\rm \mu as}$. The source size relative to Einstein ring radius $\rho = \theta_* / \theta_{\rm E} = 0.0109 \pm 0.0012$ from $u_0>0$ model implies $\theta_{\rm E} = \theta_*/\rho = 0.57\pm0.07~{\rm mas}$.

The value of $\theta_{\rm E}$ allows estimating parameters of the lens in physical units. As there remained little ambiguity between $u_0>0$ and $u_0<0$ 