Upgrades to the Event Simulation and Reconstruction for the Fermi Large Area Telescope

Understand

The pre-launch event simulation and reconstruction performed beyond our expectations for real data, essentially without modification, and made possible the immediate start of science analysis.

• But the on-orbit data exhibit unanticipated features that necessitate upgrades to both the simulation (essentially complete) and the reconstruction (ongoing).
• The major new effect encountered on orbit is the presence of "ghosts," that is, remnant detector response to particles passing through the detector before the particle that triggered the event.
• These ghosts appear primarily in the form of extra tracks and/or energy deposits.