2 research outputs found
The Galactic magnetic field as spectrograph for ultra-high energy cosmic rays
We study the influence of the regular component of the Galactic magnetic
field (GMF) on the arrival directions of ultra-high energy cosmic rays
(UHECRs). We find that, if the angular resolution of current experiments has to
be fully exploited, deflections in the GMF cannot be neglected even for E=10^20
eV protons, especially for trajectories along the Galactic plane or crossing
the Galactic center region. On the other hand, the GMF could be used as a
spectrograph to discriminate among different source models and/or primaries of
UHECRs, if its structure would be known with sufficient precision. We compare
several GMF models introduced in the literature and discuss for the example of
the AGASA data set how the significance of small-scale clustering or
correlations with given astrophysical sources are affected by the GMF. We point
out that the non-uniform exposure to the extragalactic sky induced by the GMF
should be taken into account estimating the significance of potential
(auto-)correlation signals.Comment: 11 pages, 8 figures; minor corrections, enlarged discussion, contains
an extended review on Galactic magnetic field compared to published version,
to appear in Astroparticle Physic
Small Scale Anisotropy Predictions for the Auger Observatory
We study the small scale anisotropy signal expected at the Pierre Auger
Observatory in the next 1, 5, 10, and 15 years of operation, from sources of
ultra-high energy (UHE) protons. We numerically propagate UHE protons over
cosmological distances using an injection spectrum and normalization that fits
current data up to \sim 10^{20}\eV. We characterize possible sources of
ultra-high energy cosmic rays (UHECRs) by their mean density in the local
Universe, Mpc, with between 3 and 6.
These densities span a wide range of extragalactic sites for UHECR sources,
from common to rare galaxies or even clusters of galaxies. We simulate 100
realizations for each model and calculate the two point correlation function
for events with energies above 4 \times 10^{19}\eV and above 10^{20}\eV, as
specialized to the case of the Auger telescope. We find that for r\ga 4,
Auger should be able to detect small scale anisotropies in the near future.
Distinguishing between different source densities based on cosmic ray data
alone will be more challenging than detecting a departure from isotropy and is
likely to require larger statistics of events. Combining the angular
distribution studies with the spectral shape around the GZK feature will also
help distinguish between different source scenarios.Comment: 15 pages, 6 figures, 6 tables, submitted to JCA