Theorem 8.2.5. Statistics for Poisson.
\begin{equation*}
\mu = \lambda T
\end{equation*}
\begin{equation*}
\sigma^2 = \mu
\end{equation*}
\begin{equation*}
\gamma_1 = \frac{1}{\sqrt{\mu}}
\end{equation*}
\begin{equation*}
\gamma_2 = \frac{1}{\mu}+3
\end{equation*}