Pulsars versus Dark Matter Interpretation of ATIC/PAMELA

Abstract: In this paper, we study the flux of electrons and positrons injected by pulsars and by annihilating or decaying dark matter in the context of recent ATIC, PAMELA, Fermi, and HESS data. We review the flux from a single pulsar and derive the flux from a distribution of pulsars. We point out that the particle acceleration in the pulsar magnetosphere is insufficient to explain the observed excess of electrons and positrons with energy E ~ 1 TeV and one has to take into account an additional acceleration of electrons at the termination shock between the pulsar and its wind nebula. We show that at energies less than a few hundred GeV, the flux from a continuous distribution of pulsars provides a good approximation to the expected flux from pulsars in the Australia Telescope National Facility (ATNF) catalog. At higher energies, we demonstrate that the electron/positron flux measured at the Earth will be dominated by a few young nearby pulsars, and therefore the spectrum would contain bumplike features. We argue that the presence of such features at high energies would strongly suggest a pulsar origin of the anomalous contribution to electron and positron fluxes. The absence of features either points to a dark matter origin or constrains pulsar models in such a way that the fluctuations are suppressed. Also we derive that the features can be partially smeared due to spatial variation of the energy losses during propagation.

Pulsars Versus Dark Matter: Interpretation of ATIC/PAMELA

The paper by Malyshev, Cholis, and Gelfand provides a detailed analysis of the sources of the observed excess of cosmic-ray electrons and positrons in the energy range of 10 GeV to 1 TeV, as reported by experiments such as ATIC, PAMELA, Fermi, and HESS. It contrasts two principal hypotheses: the injection of these particles by pulsars and the annihilation or decay of dark matter (DM).

The authors begin by modeling the electron and positron flux from pulsars. They emphasize that standard pulsar magnetosphere models are insufficient to account for the anomalous particle flux at energies around 1 TeV. They propose considering additional acceleration at the termination shock between the pulsar and its wind nebula. At energies less than a few hundred GeV, the flux approximation from a distribution of pulsars fits well with data from the Australia Telescope National Facility (ATNF) catalog. However, at higher energies, the Earth's observed flux is likely dominated by contributions from a few young, nearby pulsars, in which case the spectrum would exhibit distinctive bumplike features. The presence of these features would strongly suggest a pulsar origin, while their absence would favor a dark matter origin or require a reconsideration of pulsar models to suppress fluctuations.

The authors also develop theoretical predictions for the flux of electrons and positrons from dark matter. For annihilating dark matter models, the paper derives a universal power-law behavior with an index of two at low energies, provided the dark matter halo is smooth. This universal behavior presents a challenge in distinguishing the dark matter contribution from other sources solely based on spectral shape.

The analysis includes sophisticated modeling of the spatial diffusion of particles, energy loss mechanisms, and propagation effects to derive insights into the observed cosmic-ray spectra. The paper evaluates the spatial distribution of potential pulsar contributors and makes predictions about the expected spectral features.

The implications of this research are vast. If the spectral features of the cosmic-ray electron and positron flux can indeed be tied back to individual pulsars, this would have a significant impact on our understanding of both cosmic-ray sources and the potential role of pulsars in high-energy astrophysics.

In conclusion, the study provides a comprehensive framework for interpreting cosmic ray data, with strong implications for both pulsar and dark matter physics. While distinguishing between these two sources remains a challenge, the paper outlines potential observational signatures that could help resolve the origin of the cosmic-ray electron and positron excess. Future advancements in spectral and spatial resolution of cosmic-ray detectors may provide more definitive answers in this area, enhancing our understanding of these high-energy particles and the universe at large.