Inverse Compton gamma-rays from Galactic dark matter annihilation: Anisotropy signatures

High energy electrons and positrons from annihilating dark matter can imprint unique angular anisotropies on the diffuse gamma-ray flux by inverse Compton scattering off the interstellar radiation field. We develop a numerical tool to compute gamma-ray emission from such electrons and positrons produced in the smooth host halo and in substructure halos with masses down to 10^(-6)M_sun. We show that the angular power spectrum from inverse Compton scattering is exponentially suppressed below an angular scale determined by the diffusion length of electrons and positrons. We also find that the total flux and the shape of the angular power spectrum depends sensitively on the spatial distribution of subhalos in the Milky Way. Finally, the contribution from the smooth host halo component to the gamma-ray mean intensity is negligibly small compared to subhalos.

💡 Research Summary

The paper investigates a novel indirect‑detection channel for particle dark matter (DM) in the Milky Way: high‑energy electrons and positrons produced by DM annihilation that up‑scatter photons of the interstellar radiation field (ISRF) via inverse Compton scattering (ICS), thereby generating diffuse gamma‑ray emission. The authors develop a comprehensive numerical framework that simultaneously treats two distinct sources of these leptons: (i) the smooth Galactic DM halo, modeled with a Navarro–Frenk–White (NFW) density profile, and (ii) a population of subhalos (or “clumps”) whose masses extend down to the theoretical cutoff of ∼10⁻⁶ M⊙. The subhalo mass function, spatial distribution, and internal density profiles are taken from state‑of‑the‑art N‑body simulations, allowing the authors to explore scenarios ranging from a centrally concentrated subhalo population to a more isotropic, halo‑wide distribution.

A key physical ingredient is the propagation of the injected electrons/positrons through the Galactic magnetic field and radiation fields. The authors adopt an energy‑dependent diffusion coefficient D(E) and include synchrotron, bremsstrahlung, and especially inverse‑Compton energy losses, encapsulated in a loss rate b(E). From these, they compute the diffusion length λ_D(E)=√