Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Measurement of the Cosmic Ray e+ plus e- spectrum from 20 GeV to 1 TeV with the Fermi Large Area Telescope

Fermi/LAT Collaboration

Abstract

Designed as a high-sensitivity gamma-ray observatory, the Fermi Large Area Telescope is also an electron detector with a large acceptance exceeding 2m^2 sr at 300 GeV. Building on the gamma-ray analysis, we have developed an efficient electron detection strategy which provides sufficient background rejection for measurement of the steeply-falling electron spectrum up to 1 TeV. Our high precision data show that the electron spectrum falls with energy as E^(-3.0) and does not exhibit prominent spectral features. Interpretations in terms of a conventional diffusive model as well as a potential local extra component are briefly discussed.

Measurement of the Cosmic Ray e+ plus e- spectrum from 20 GeV to 1 TeV with the Fermi Large Area Telescope

Abstract

Designed as a high-sensitivity gamma-ray observatory, the Fermi Large Area Telescope is also an electron detector with a large acceptance exceeding 2m^2 sr at 300 GeV. Building on the gamma-ray analysis, we have developed an efficient electron detection strategy which provides sufficient background rejection for measurement of the steeply-falling electron spectrum up to 1 TeV. Our high precision data show that the electron spectrum falls with energy as E^(-3.0) and does not exhibit prominent spectral features. Interpretations in terms of a conventional diffusive model as well as a potential local extra component are briefly discussed.

Paper Structure

This paper contains 3 figures, 1 table.

Figures (3)

  • Figure 1: (color online) Energy resolution for the LAT after electron selection; the full widths of the smallest energy window containing the 68% and the 95% of the energy dispersion distribution are shown. The comparison with beam test data up to 282 GeV and for on-axis and at 60$^\circ$ incidence shown in the figure indicates good agreement with the resolution estimated from the simulation.
  • Figure 2: (color online) Distribution of the transverse sizes of the showers (above 150 GeV) in the CAL at an intermediate stage of the selection, where a large contamination from protons is still visible. Flight data (black points) and MC (gray solid line) show very good agreement; the underlying distributions of electron and hadron samples are visible in the left (red) and the right (blue) peaks respectively.
  • Figure 3: (color) The Fermi LAT CR electron spectrum (red filled circles). Systematic errors are shown by the gray band. The two-headed arrow in the top-right corner of the figure gives size and direction of the rigid shift of the spectrum implied by a shift of $^{+5\%}_{-10 \%}$ of the absolute energy, corresponding to the present estimate of the uncertainty of the LAT energy scale. Other high-energy measurements and a conventional diffusive model SMR2004 are shown.