Speaker
Iris Gebauer
Description
The positron fluxes measured by PAMELA and most recently
AMS-02, show an excess far above the expectations of secondary positron
production in the ISM. These locally observed energetic positrons
require a near-by source of even more energetic positrons.
Among the possible explanations for a primary source of such positrons,
unaccounted astrophysical point sources or dark
matter (DM) decay or annihilation are the most promising ones.
In this context the level of
anisotropy in the locally measured $e^{\pm}$ arrival directions is a key
observable to
differentiate between point sources, such as pulsars, and the DM
hypothesis. Compared to protons and nuclei, energetic $e^{\pm}$ lose
energy on
short timescales. Therefore, any source of energetic $e^{\pm}$ needs
to be
located in the solar neighborhood, and thus in the proximity of
the local bubble, an underdense region surrounding the Sun which is
assumed to have its origin in about 20 supernova explosions in the
past 10-20 Myrs. This rather peculiar environment may have a
non-negligible impact on local cosmic ray transport and in particular
on the expected level of anisotropy.
Using general assumptions on the local variations of the diffusion
coefficient, as expected for the local bubble, we discuss the impact of
this structure on the observed $e^{\pm}$ spectra and the local
anisotropy.
We find that under reasonable assumptions about the diffusion
coefficient, both the spectra and the local level on anisotropy are
affected in a
sizeable way. We further find that a good description of the AMS-02
data is
possible, while the level of anisotropy may be decreased by up to 80%.
| Registration number following "ICRC2015-I/" | 717 |
|---|---|
| Collaboration | -- not specified -- |
Authors
Daniele Gaggero
Iris Gebauer
Mr
Matthias Weinreuter
(KIT)
Simon Michael Kunz
(KIT - Karlsruhe Institute of Technology (DE))
