A Novel Analytical Model of the Magnetic Field Configuration in the Galactic Center Explaining the Diffuse Gamma-Ray Emission (ICRC-2019)

TL;DR

This paper introduces a new 3D analytical model of the magnetic field and gas distribution in the Galactic Center, explaining diffuse gamma-ray emission and highlighting the importance of magnetic field configuration in cosmic ray propagation.

Contribution

It presents the first divergence-free 3D magnetic field model in the Galactic Center and a detailed gas distribution model, advancing understanding of gamma-ray emission origins.

Findings

The model explains gamma-ray emission at small longitudes.

Magnetic field configuration significantly affects cosmic ray propagation.

The magnetic field model aligns with polarization observations.

Abstract

Reliable identification of the origin of the high-energy non-thermal emission from the Galactic Center (GC) is not achievable without adequate consideration of the ambient conditions such as the magnetic field configuration or gas distribution. In a first step, we present a model that can explain the diffuse gamma-ray emission as measured by H.E.S.S. for small longitudes in the Galactic Center region but comes to grief with higher longitudes. The model is given via the solution of a transport equation that allows for a radial dependency of the mass distribution. In order to move from this semi-analytical approximation toward a full understanding of the PeVatron signature, we present a new 3D analytical model of the gas distribution in the Central Molecular Zone (CMZ). Furthermore, we derive for the first time a 3D model of the magnetic field configuration and strength in the CMZ, which is analytical and divergence-free. The model is built via a combination of a model for the diffuse inter-cloud medium, local molecular clouds and non-thermal filaments at which local information are based on investigations from previous works and the molecular gas density. It can be shown that without an efficient longitudinal CR entrapment, a single source at the center does not facilely suffice the diffuse gamma-ray detection. Further, we show that the new magnetic field model GBFD19 is compatible with recent polarization data and has a significant impact on the longitudinal profiles of CR propagation.