Fermi Gamma-ray Space Telescope

Geomagnetic effects on the CR Electron Spectrum measured by the Fermi-LAT

A. Manfreda
N. Di Lalla, C. Sgr, on behalf of the Fermi-LAT Collaboration

Abstract:

The Fermi Large Area Telescope operates at an altitude of 565 km in an orbit with a 26.5 inclination angle. Such an orbit spans a range in geomagnetic rigidity cut-off, which corresponds to a difference of several GeV in the minimum energy required for a galactic cosmic ray to reach the detector. As a consequence, an accurate measurement of the primary cosmic-ray electron and positron (CRE) spectrum, in the energy range from a few GeV to a few tens of GeV, requires sampling the population of CREs in different geomagnetic regions. We present the detail of this analysis, which allows us to extend the lower limit of the new Pass 8 CRE spectrum measurement. We made use of a dedicated simulation of charged particle tracks in the geomagnetic field to estimate the fraction of events lost due to the magnetic shadow of the Earth.