Decay of the fundamental solution of fractional laplacian equations

Question

It is well known that the fundamental solution $\Gamma_1$ in $\mathbb{R}^n$ of the Schrödinger operator $-\Delta + 1$ decays exponentially fast, viz. $|\Gamma_1(x)| \leq C_1 \mathrm{e}^{-C_2|x|}$ as $|x| \to +\infty$. I have read some comments in several papers about a different behavior of the fundamental solution $\Gamma_s$, $0<2<1$, of the fractional Schrödinger operator $(-\Delta)^s +1$; it should decay like $1/|x|^{n+2s}$. Unluckily, I cannot find a good reference for this fact, and I wonder if somebody knows a paper or has some hint for the proof.