A unified solution to the anisotropy and gradient problems

TL;DR

This paper proposes a unified model linking cosmic ray escape times and magnetic turbulence to simultaneously resolve discrepancies in gamma-ray emission profiles and cosmic ray anisotropy observations.

Contribution

It introduces a physically motivated correlation between CR escape time and magnetic turbulence, providing a natural solution to multiple observational anomalies.

Findings

Models fit a wide range of CR spectra

Reproduce CR anisotropy in 100 GeV - 10 TeV range

Match Fermi-LAT gamma-ray longitude distribution

Abstract

The Fermi-LAT collaboration recently confirmed a discrepancy between the observed longitudinal profile of gamma-ray diffuse emission from the Galaxy and that computed with numerical codes assuming that Cosmic Rays (CRs) are produced by Galactic supernova remnants; the accurate Fermi-LAT measurements make this anomaly hardly explainable in terms of conventional diffusion schemes. Moreover, experimental data from both Muon detector and Extensive Air Shower experiments about the large scale dipole anisotropy of CRs can hardly be compatible with model predictions within the framework of conventional isotropic and homogeneous propagation. We argue that, accounting for a well physically motivated correlation between the CR escape time and the spatially dependent magnetic turbulence power, it is possible to solve both problems at the same time in a very natural way. Indeed, by exploiting this correlation, we find propagation models that fit a wide set of CR primary and secondary spectra, and consistently reproduce the CR anisotropy in the energy range 100 GeV - 10 TeV and the gamma-ray longitude distribution recently measured by Fermi-LAT.