Upper mass limit of the perturbing planet in the WASP-43 system. The best ﹩{\rm{\Delta }}{\chi }_{{\rm{red}}}^{2}﹩ values, binned with a period ratio of 0.05, are shown as the black dotted line. The upper mass limits for TTV amplitudes of 5, 15, and 25 s are represented by the blue dashed–dotted, green dashed, and red solid lines, respectively. The white vertical line represents the orbital period of WASP-43 b. The black vertical lines, from left to right, indicate the orbital period resonances of 2:1, 1:2, 1:3, and 1:4. The contour illustrates the ﹩{\rm{\Delta }}{\chi }_{{\rm{red}}}^{2}﹩ values from comparing the best TTV model to the best linear model. The unstable orbit region is shown as the shaded black area.