Gamma rays, electrons and positrons up to 3 TeV with the Fermi Gamma-ray Space Telescope

TL;DR

This paper discusses the Fermi Gamma-ray Space Telescope's LAT instrument, highlighting its performance in measuring gamma rays, electrons, and positrons up to 3 TeV, and reviews key scientific results from four years of data.

Contribution

It provides detailed performance analysis of the LAT, especially its calorimeter, and reports on high-energy astrophysical measurements extending to 3 TeV.

Findings

Effective energy measurement up to 3 TeV for gamma rays, electrons, and positrons.

Key scientific results include spectra of extragalactic diffuse emission and cosmic-ray components.

Validation of the LAT's capability to study high-energy astrophysical phenomena.

Abstract

The Fermi Gamma-ray Space Telescope (formerly known as Gamma-ray Large Area Space Telescope, GLAST) was successfully launched on June 11 2008. Its main instrument is the Large Area Telescope (LAT), which detects gamma rays from 20 MeV to more than 300 GeV. It is a pair-conversion telescope with 16 identical towers (tracker and calorimeter), covered by an anti-coincidence detector to reject charged particles. The calorimeter is a hodoscopic array of CsI(Tl) crystals, arranged in 8 alternating orthogonal layers, with a total thickness of 8.6 radiation lengths. In this paper we will present the performance of the LAT, with special attention to the calorimeter, which provides a good energy measurement up to 3 TeV. We will also review some of its scientific results after 4 years of operation, focusing on measurements which extend up to very high energy, such as the spectrum of the extragalactic diffuse emission, the spectrum of cosmic electrons and the positron fraction.