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

Evidence for a hadronic origin of the Fermi Bubbles, formed by outflows from star-forming regions

Aug 4, 2015, 11:30 AM
Yantgze 1 (World Forum)

Yantgze 1

World Forum

Churchillplein 10 2517 JW Den Haag The Netherlands
Oral contribution GA-TH Parallel GA14 GAL / Bubbles etc


Wim De Boer (KIT - Karlsruhe Institute of Technology (DE))


The Fermi-LAT 6-year data provide a detailed map of the diffuse gamma-ray sky for which the main contributions originate from neutral pion decay, bremsstrahlung and inverse Compton scattering. The energy spectra of these contributions are known from laboratory experiments and can be used as templates to fit the energy spectra of the Fermi data in each direction, thus providing the normalization, and hence the fluxes, for the various contributions in each direction. These contributions describe the data well, except for the regions of the Fermi Bubbles, the Galactic Bar and the spiral arms. In these regions one needs an additional component corresponding to the decay of neutral pions produced by CR nuclei with a spectral index of $E^{-2}$, which can be attributed to source cosmic rays (SCR), i.e. cosmic rays (CR) trapped inside the source and producing mainly pions in the enhanced gas density of the shock wave. The hard $E^{-2}$ spectrum is the hardest imaginable CR spectrum, predicted only for diffuse shock wave acceleration in supernova remnants (SNRs). The SCR interpretation is supported by the fact that i) the energetics of this contribution is consistent with a SNR rate of 3 per century and ii) the spatial distributions of this hard component coincides with the spatial distribution of 1.8 MeV gamma rays from 26Al, a radioactive nucleus produced in SNRs as well. The morphology of the hard Fermi component and 1.8 MeV gamma rays shows in both cases clearly the imprint from the Galactic Bar and the tangent point of the nearest spiral arm. The Fermi Bubbles have the same hard $E^{-2} spectrum, suggesting that they are outflows from star-forming regions near the Galactic center with the CRs trapped inside this plasma. In this case the CR spectra are not softened by diffusion.
Collaboration -- not specified --
Registration number following "ICRC2015-I/" 1096

Primary authors

Iris Gebauer (KIT - Karlsruhe Institute of Technology (DE)) Simon Michael Kunz (KIT - Karlsruhe Institute of Technology (DE)) Wim De Boer (KIT - Karlsruhe Institute of Technology (DE))

Presentation materials