Does the SN rate explain the very high energy cosmic rays in the central 200 pc of our Galaxy?

Abstract

The H.E.S.S. collaboration revealed the presence of a very high energy (VHE) diffuse emission in the inner 100pc of the Galaxy in close correlation with the Central Molecular Zone (CMZ). Recently, they deduced from this emission a cosmic-ray (CR) over-density in the region with a local peak toward the Galactic Center (GC) and proposed a diffusive scenario with a stationary source at the GC to explain it. However, the high supernovae (SN) rate in the GC must also create a sustained CR injection in the region via the shocks produced at the time of their explosion. Considering typical diffusion coefficient close the interstellar medium (ISM) value yields to a diffuse escape time much lower than the recurrence time between each SN explosion, showing that a steady state model will fail to reproduce the data. This work aims to study the impact of the spatial and temporal distribution of SNs in the CMZ on the VHE emission morphology and spectrum: we build a 3D model of VHE CR injection and diffusive propagation with a realistic gas distribution. We show that a peaked gamma-ray profile towards the GC can be obtained using realistic SN spatial distribution taking into account the central massive star cluster. We conclude that the contribution of SNs can not be neglected, in particular at large longitudes, however an additional CR injection at the GC is required to reproduce the very central excess.