Fermi Gamma-ray Space Telescope

Event Selection and Systematics Evaluation of the Cosmic-ray Electrons Analysis

M. Negro
P. Bruel, on behalf of the LAT Collaboration

Abstract:

Extending the Fermi Large Area Telescope (LAT) measurement of the cosmic-ray electron (CRE) inclusive spectrum above 1 TeV uses new observables which describe electromagnetic shower development in the LAT calorimeter. These new observables are sensitive to LAT geometry and to the calorimeter crystal saturation effects and therefore require careful study. We used dedicated corrections to fine tune the agreement between flight and simulated data sets for the most relevant observables. These corrections and possible event selection uncertainties can be used to estimate systematic errors associated with the CRE spectrum measurement. Additionally, exploring the geomagnetic cut-off with seven years of Pass 8 CRE data reveals a 3.7% shift of the cut-off energy with respect to expectations from tracer codes. This is slightly larger than the previously published shift of 2.5% and is related to updated LAT calibrations. Rescaling the LAT energy with the cut-off shift brings the Pass8 CRE spectrum closer to recently published measurements.