Diffusive Cosmic Ray Acceleration at the Galactic Centre

Abstract

The diffuse TeV emission detected from the inner $\sim 2^{\circ }$ of the Galaxy appears to be strongly correlated with the distribution of molecular gas along the Galactic ridge. Although it is not yet entirely clear whether the origin of the TeV photons is due to hadronic or leptonic interactions, the tight correlation of the intensity distribution with the molecular gas strongly points to a pionic-decay process involving relativistic protons. But the spectrum of the TeV radiation---a power law with index $\alpha \approx -2.3$---cannot be accommodated easily with the much steeper distribution of cosmic rays seen at Earth. In earlier work, we examined the possible sources of these relativistic protons and concluded that neither the supermassive black hole Sagittarius A* (identified with the HESS source J1745-290), nor several pulsar wind nebulae dispersed along the Galactic plane, could produce a TeV emission profile morphologically similar to that seen by HESS. We concluded from this earlier study that only relativistic protons accelerated throughout the inter-cloud medium could account for the observed diffuse TeV emission from this region. In this paper, we develop a model for diffusive proton acceleration driven by a turbulent Alfvénic magnetic field present throughout the gaseous medium. Though circumstantial, this appears to be the first evidence that at least some cosmic rays are accelerated diffusively within the inner $\sim 300$ pc of the Galaxy.

Accepted for publication in MNRAS letters

References in corpus (4)

• The 3rd IBIS/ISGRI soft gamma-ray survey catalog
• A Possible Link Between the Galactic Center HESS Source and Sgr A*
• Ultra-High-Energy Cosmic Rays from the Radio Lobes of AGNs
• Diffuse TeV Emission at the Galactic Centre

Cited by in corpus (13)

• Observational signatures of particle acceleration in supernova remnants
• Magnetized Accretion and Dead Zones in Protostellar Disks
• Non-Thermal Insights on Mass and Energy Flows Through the Galactic Centre and into the Fermi Bubbles
• Concurrent X-ray, near-infrared, sub-millimeter, and GeV gamma-ray observations of Sgr A*
• Diffuse Hard X-ray Emission in Starburst Galaxies as Synchrotron from Very High Energy Electrons
• Gamma rays from the Galactic Centre region: a review
• Hadronic origin of multi-TeV gamma rays and neutrinos from low-luminosity active galactic nuclei: implications of past activities of the Galactic center
• Molecular and Atomic Gas toward HESS J1745-303 in the Galactic Center: Further Support for the Hadronic Scenario
• A Numerical Assessment of Cosmic-ray Energy Diffusion through Turbulent Media
• Stochastic Acceleration of Cosmic Rays in the Central Molecular Zone of the Galaxy
• Diffusive Cosmic-ray Acceleration in Sagittarius A*
• Assessing the Feasibility of Cosmic-Ray Acceleration by Magnetic Turbulence at the Galactic Center
• Modification of cosmic-ray energy spectra by stochastic acceleration