  The decay of $J/\psi$ to three photons is studied using
$\psi(3686)\to\pi^+\pi^-J/\psi$ in a sample of $1.0641\times10^8$ $\psi(3686)$
events collected with the BESIII detector. Evidence of the direct decay of
$\eta_c$ to two photons, $\eta_c\to\gamma\gamma$, is reported, and the product
branching fraction is determined to be
$\mathcal{B}(J/\psi\to\gamma\eta_c,\eta_c\to
\gamma\gamma)=(4.5\pm1.2\pm0.6)\times10^{-6}$, where the first error is
statistical and the second is systematic. The branching fraction for
$J/\psi\to3\gamma$ is measured to be $(11.3\pm1.8\pm2.0)\times 10^{-6}$ with
improved precision.
