Extending the Galactic Cosmic Ray electron + positron spectrum measured by the Fermi LAT

TL;DR

This paper reports on extending the measurement of the Galactic Cosmic Ray electron and positron spectrum to lower energies using the Fermi LAT, accounting for geomagnetic effects to improve the spectrum's lower energy limit.

Contribution

It introduces a method to extend the GCR electron + positron spectrum measurement to lower energies by analyzing geomagnetic position effects.

Findings

Extended the GCR electron + positron spectrum measurement down to ~5 GeV.

Demonstrated the importance of geomagnetic position in spectrum analysis.

Improved understanding of low-energy cosmic ray measurements.

Abstract

Launched on the 11th of June 2008, the Fermi Large Area Telescope (LAT) has made several outstanding scientific contributions to the high energy astrophysics community. One of these contributions was the high statistics measurement of the Galactic Cosmic Ray (GCR) electron + positron spectrum from 20 GeV to 1 TeV. The Fermi satellite is in a nearly circular orbit with an inclination of 25.6 degrees at an altitude of 565 km. Given this orbit it is possible to measure the GCR electrons + positrons down to roughly 5 GeV. However, this lower limit in energy is highly dependent on the orbital position of the LAT in geomagnetic coordinates due to the rigidity cutoff. In order to measure the spectrum down to these energies it is necessary to sample the population of electrons + positrons in several different geomagnetic positions. In this poster we present the analysis performed to extend the lower limit in energy of the GCR electron + positron spectrum measured by the Fermi LAT.