July 29, 2015 to August 6, 2015
World Forum
Europe/Amsterdam timezone

Interacting Cosmic Rays with Molecular Clouds in the Galactic Center

Jul 31, 2015, 11:00 AM
15m
Yangtze 1 (World Forum)

Yangtze 1

World Forum

Churchillplein 10 2517 JW Den Haag The Netherlands
Oral contribution GA-TH Parallel GA05 GeV excess GalCen

Speaker

Chris Gordon (University of Canterbury)

Description

The High-Energy Stereoscopic System (HESS) has detected diffuse TeV emission correlated with the distribution of molecular gas along the Ridge at the Galactic Center. Diffuse, nonthermal emission is also seen by the Fermi large area telescope (Fermi-LAT) in the GeV range and by radio telescopes in the GHz range. Additionally, there is a distinct, spherically symmetric excess of gamma rays seen by Fermi-LAT in the GeV range. A cosmic ray flare, occurring in the Galactic Center, 10 000 years ago has been proposed to explain the TeV Ridge (Aharonian et al. 2006). An alternative, steady-state model explaining all three data sets (TeV, GeV, and radio) invokes purely leptonic processes (Yusef-Zadeh et al. 2013). We show that the flare model from the Galactic Center also provides an acceptable fit to the GeV and radio data, provided the diffusion coefficient is energy independent. However, if Kolmogorov-type turbulence is assumed for the diffusion coefficient, we find that two flares are needed, one for the TeV data (occurring approximately 10 000 years ago) and an older one for the GeV data (approximately a hundred thousand years old). We find that the flare models we investigate do not fit the spherically symmetric GeV excess as well as the usual generalized Navarro-Frenk-White spatial profile, but are better suited to explaining the Ridge. We also show that a range of single-zone, steady-state models are able to explain all three spectral data sets. A low gas density is needed for the steady-state model to be wind driven. Higher gas densities can be accommodated by an energy independent diffusion or streaming based steady-state model. Additionally, we investigate how the flare and steady-state models may be distinguished with future gamma-ray data looking for a spatial dependence of the gamma-ray spectral index.
Registration number following "ICRC2015-I/" 404
Collaboration -- not specified --

Primary author

Chris Gordon (University of Canterbury)

Co-authors

Dr Oscar Macias (University of Canterbury) Dr Roland Crocker (ANU) Stefano Profumo

Presentation materials