Evidence for $eta_{c} rightarrow gammagamma$ and Measurement of $J/psirightarrow 3gamma$

The decay of $J/psi$ to three photons is studied using $psi(3686)topi^+pi^-J/psi$ in a sample of $1.0641times10^8$ $psi(3686)$ events collected with the BESIII detector. Evidence of the direct decay of $eta_c$ to two photons, $eta_ctogammagamma$, is reported, and the product branching fraction is determined to be $mathcal{B}(J/psitogammaeta_c,eta_cto gammagamma)=(4.5pm1.2pm0.6)times10^{-6}$, where the first error is statistical and the second is systematic. The branching fraction for $J/psito3gamma$ is measured to be $(11.3pm1.8pm2.0)times 10^{-6}$ with improved precision.