Electron and photon energy calibration with the ATLAS detector using data collected in 2015 at $\sqrt{s} = 13 \mathrm{\ Te\kern -0.1em V}$

This document describes the calibration of the energy of electrons and photons, as implemented by the ATLAS experiment for proton-proton collision data collected in 2015 and the first part of 2016 at $\sqrt{s}=13$ TeV. The strategy adopted was developed during LHC Run-1 and is based both on simulations and on data collected during 2015. The steps of the calibration scheme based on simulation have been fully re-optimised using the updated detector description and reconstruction procedures. The data-driven corrections have been re-evaluated or extrapolated from Run-1 results, in the cases where the amount of data collected in 2015 was insufficient. The uncertainty model has been updated in order to include these extrapolation uncertainties.