  We study $L^p$-boundedness of the Bochner-Riesz means for critical magnetic
Schr\"odinger operators $\mathcal{L}_{\bf A}$ in ${\mathbb{R}^2}$, which
involve the physcial Aharonov-Bohm potential. We show that for $1\leq p\leq
+\infty$ and $p\neq 2$, the Bochner-Riesz operator
$S_{\lambda}^\delta(\mathcal{L}_{\bf A})$ of order $\delta$ is bounded on
$L^p(\mathbb{R}^2)$ if and only if $\delta>\max\big\{0,
2\big|1/2-1/p\big|-1/2\big\}$. The new ingredient of the proof is to obtain the
localized $L^4(\mathbb R^2)$ estimate of $S_{\lambda}^\delta(\mathcal{L}_{\bf
A})$, whose kernel is heavily affected by the physical magnetic diffraction,
and more singular than the classical Bochner-Riesz means
$S_{\lambda}^\delta(\Delta)$ for the Laplacian $\Delta$ in $\mathbb{R}^2$.
