latest [@DB_2015]. The reduction comes from the improvements in the correction of position and time dependence.

Nonlinearity in the energy response of an AD originates from two dominant sources: particle-dependent nonlinear light yield of the scintillator and charge-dependent nonlinearity in the PMT readout electronics. Each effect is at the level of 10%. We have constructed a semi-empirical model that predicts the reconstructed energy for a particle assuming a specific energy deposited in the scintillator. The model contains four parameters: Birks’ constant, the relative contribution to the total light yield from Cherenkov radiation, and the amplitude and scale of an exponential correction describing the non-linear electronics response. This exponential form of the electronics response is motivated by Monte Carlo (MC) and data; it has been confirmed with an independent FADC measurement. Besides the calibration references used in the energy scale studies, a broad set of calibration sources were deployed into the two ADs of EH1 using the ACUs and a manual calibration system [@huanghx] during the shutdown in the summer of 2012. The energy nonlinearity, i.e. the absolute energy scale, is determined to $<1$% above 2 MeV.

To select reactor antineutrino events, the PMT flasher background is rejected first. The prompt 