Nuclear modification factor $R_{\rm AA}$ for isolated photons at $\sqrt{s_{\rm NN}}=$ 5.02 TeV for isolation-cone radii $R=$ 0.2 (black) and $R=$ 0.4 (blue). Error bars and boxes are the statistical and systematic uncertainties, respectively. The isolated-photon $R_{\rm AA}$ is compared to that of charged particles [22] and charged pions [24] from ALICE, and to the ratio of the $\text{Z}^{0}$-boson yield in each centrality class to the 0$-$90% class measured by CMS [35]. The bands correspond to pQCD calculations with JETPHOX for Pb$-$Pb collisions (nPDF) for 0$-$100% centrality over pp collisions (PDF). The width of each band corresponds to the scale and PDF uncertainties. The normalisation uncertainties are represented as a red box centred at unity. The solid line in the most peripheral centrality class 70$-$90% at $R_{\rm AA}=$ 0.82 corresponds to the HG-PYTHIA model expectation [41].