The Fermi Large Area Telescope On Orbit: Event Classification, Instrument Response Functions, and Calibration

Understand

The Fermi Large Area Telescope (Fermi-LAT, hereafter LAT), the primary instrument on the Fermi Gamma-ray Space Telescope (Fermi) mission, is an imaging, wide field-of-view, high-energy \gamma-ray telescope, covering the energy range from 20 MeV to more than 300 GeV.

• During the first years of the mission the LAT team has gained considerable insight into the in-flight performance of the instrument.
• Accordingly, we have updated the analysis used to reduce LAT data for public release as well as the Instrument Response Functions (IRFs), the description of the instrument performance provided for data analysis.
• In this paper we describe the effects that motivated these updates.