model. In these cases, the positive/negative $u_0$ degeneracy is very severe (maximum $\Delta\chi^2=2.4$). Significant negative blending [@park04] suggests that the last three models presented are not correct solutions, i.e., neglecting parallax or lens orbital motion results in wrong parameter estimates. The parameters were fitted using Monte Carlo Markov Chains. We checked how inclusion of data collected during four nights around $t_0$ influences the parameters fitted. The 21 additional points increased $\chi^2$ by $25.1$. The largest change in values of parameters fitted was only $0.33\sigma$ in case of $t_{\rm E}$.

Table \[tab:res\] reveals that there is a degeneracy between $\pi_{{\rm E}, N}$ (which is a proxy for component of ${{\bm{\pi}}}_{{\rm E}}$ perpendicular to the direction of the projected Sun’s acceleration) and $\gamma_{\perp}$. This degeneracy is well known [@skowron11; @batista11]. There is also a suggestion that the analyzed event is a subject to degeneracy between $\pi_{{\rm E}, E}$ and $\gamma_{\parallel}$, which was presented by @park13. The reason of the second degeneracy is not well understood.

The model that includes both the microlensing parallax and orbital motion of the lens gives $\chi^2$ smaller by $24.5$ than any other model. This shows that the effects of the lens orbital motion are significant yet not 