A Search for Cosmic-ray Proton Anisotropy with the Fermi Large Area Telescope

TL;DR

This paper reports the first full-sky measurement of cosmic-ray proton anisotropy in the 100 GeV to 10 TeV range using the Fermi LAT, providing insights into local magnetic fields and potential nearby sources.

Contribution

It presents the first full-sky 2D anisotropy measurement of cosmic-ray protons with the Fermi LAT, covering all angular scales and energies from 100 GeV to 10 TeV.

Findings

Detection of anisotropy in cosmic-ray protons

Full-sky angular power spectrum measurement

Complementary to existing TeV anisotropy studies

Abstract

In eight years of operation, the Fermi Large Area Telescope (LAT) has detected a large sample of cosmic-ray protons. The LAT's wide field of view and full-sky coverage make it an excellent instrument for studying anisotropy in the arrival directions of protons at all angular scales. These capabilities enable the LAT to make a full-sky 2D measurement of cosmic-ray proton anisotropy complementary to many recent TeV measurements, which are only sensitive to the right ascension component of the anisotropy. Any detected anisotropy probes the structure of the local interstellar magnetic field or could indicate the presence of a nearby source. We present the first results from the Fermi-LAT Collaboration on the full-sky angular power spectrum of protons from approximately 100 GeV - 10 TeV.