Diffuse gamma-ray emission in Cygnus X: Comments to Fornieri & Zhang 2022

TL;DR

This paper critiques a recent study on gamma-ray emission in Cygnus X, clarifying that the previously derived particle diffusion coefficients are inaccurate and emphasizing the importance of the injection process in modeling high-energy emissions.

Contribution

The paper provides a critical correction to previous diffusion coefficient calculations and highlights the significance of particle injection processes in gamma-ray emission modeling.

Findings

Previous diffusion coefficients are incorrect by an order of magnitude.

Particle injection significantly influences high-energy gamma-ray emission.

Corrected diffusion modeling aligns better with observed data.

Abstract

High energy emissions near particle accelerators provide unique windows to probe the particle acceleration and ensuing escape process determined by local medium properties, particularly the turbulence properties. It has been demonstrated both theoretically and observationally that particle diffusion in local environment can differ from the averaged values inferred from the CR global propagation in the Galaxy determined by local medium, particularly magnetic field and turbulence. A recent publication by Fornieri & Zhang (2022) computed particle transport employing the formalism of fast modes scattering calculation from Yan & Lazarian (2008) and the MHD modes composition results from Makwana & Yan (2020) and Zhang et al. (2020). The authors claim that the Cygnus X observations from HAWC and Ferm-LAT can be reproduced (Abeysekara et al., 2021; Ackermann et al., 2011). We clarify in this paper that the particle diffusion coefficients they obtained do not correspond to their adopted turbulence and medium properties and are incorrect by an order of magnitude. We also point out that the injection process also plays an indispensable role in determining the high energy particle distribution and the resulting gamma-ray emission.