Cosmic ray electron anisotropies as a tool to discriminate between exotic and astrophysical sources

TL;DR

This paper explores how measuring electron anisotropies can help distinguish whether the observed cosmic ray excess originates from dark matter annihilation or nearby astrophysical sources like pulsars.

Contribution

It calculates the expected electron flux anisotropies from known gamma-ray pulsars and dark matter scenarios, assessing the potential for detection by Fermi.

Findings

Small dipole anisotropies may be detectable by Fermi.

Anisotropy signatures differ between dark matter and pulsar models.

The study provides a framework for using anisotropy measurements to identify cosmic ray sources.

Abstract

Recent results from the PAMELA, ATIC, PPB BETS and Fermi collaborations extend the energy range in the electron flux measurement up to unexplored energies in the hundred GeVs range confirming the bump starting at about 10GeV already suggested by HEAT and AMS01 data . This bump can be explained by annihilating dark matter in the context of exotic physics, or by nearby astrophysical sources e.g. pulsars. In order to discriminate between competing models for primary positron production, the study of anisotropies ,complementary to the spectrum determination, shows up as new tool to look for the origin of the lepton excess. In this letter we calculate the contribution to the electron flux given by the collection of all known gamma ray pulsars (as listed in the ATNF catalogue) and by annihilating dark matter both in case of a clumpy halo or in case the excess can be atributed to a nearby sizeable dark matter clump. We address the problem of the electron anisotropy in both scenarios and estimate the prospect that a small dipole anisotropy can be found by the Fermi observatory.