We present 11.2 \mu m observations of the gravitationally lensed , radio-loud z _ { s } = 2.64 quasar MG0414+0534 , obtained using the Michelle camera on Gemini North .
We find a flux ratio anomaly of A 2 / A 1 = 0.93 \pm 0.02 for the quasar images A1 and A2 .
When combined with the 11.7 \mu m measurements from Minezaki et al .
( 2009 ) , the A 2 / A 1 flux ratio is nearly 5 \sigma from the expected ratio for a model based on the two visible lens galaxies .
The mid-IR flux ratio anomaly can be explained by a satellite ( substructure ) , 0 \farcs 3 Northeast of image A2 , as can the detailed VLBI structures of the jet produced by the quasar .
When we combine the mid-IR flux ratios with high-resolution VLBI measurements , we find a best-fit mass between 10 ^ { 6.2 } and 10 ^ { 7.5 } M _ { \odot } inside the Einstein radius for a satellite substructure modeled as a singular isothermal sphere at the redshift of the main lens ( z _ { l } = 0.96 ) .
We are unable to set an interesting limit on the mass to light ratio due to its proximity to the quasar image A2 .
While the observations used here were technically difficult , surveys of flux anomalies in gravitational lenses with the James~ { } Webb~ { } Space~ { } Telescope will be simple , fast , and should well constrain the abundance of substructure in dark matter haloes .