Uniform bounds for maximal flat periods on $SL_n(\mathbb{R})$

Let $X$ be a compact locally symmetric space associated to $SL_n(\mathbb{R})$ and $Y \subset X$ a maximal flat submanifold, not necessarily closed. Using a Euclidean approximation, we give an upper bound in the spectral aspect for Maass forms integrated against a smooth cutoff function on $Y$ .