The Calibrations of the DAMPE γ-Ray Effective Area

The Dark Matter Particle Explorer (DAMPE) is a cosmic-ray detector as well as a pair-converting γ-ray telescope. The effective area, reflecting the geometrical cross-section area, the γ-ray conversion probability, and the photon selection efficiency, is important in γ-ray analyses. In this work, we find a significant time variation in the effective area, as large as ∼−4% yr−1 at 2 GeV for the high-energy trigger. We derive the data-based correction factors to the effective areas and apply corrections to both the effective areas and the exposure maps. The calibrated exposure can be ∼12% smaller than the Monte Carlo one on average at 2 GeV. The calibration is further verified using the observation of the Vela pulsar, showing the spectral parameters with the correction are more consistent with those in the Fermi-LAT catalog than the ones without correction. All the corrections are now implemented in the latest version of the DAMPE γ-ray analysis toolkit DmpST.