3 research outputs found
Deflection of ultra high energy cosmic rays by the galactic magnetic field: from the sources to the detector
We report the results of 3D simulations of the trajectories of ultra-high
energy protons and Fe nuclei (with energies and ) propagating through the galactic magnetic field from the
sources to the detector. A uniform distribution of anti-particles is
backtracked from the detector, at the Earth, to the halo of the Galaxy. We
assume an axisymmetric, large scale spiral magnetic field permeating both the
disc and the halo. A normal field component to the galactic plane () is
also included in part of the simulations. We find that the presence of a large
scale galactic magnetic field does not generally affect the arrival directions
of the protons, although the inclusion of a component may cause
significant deflection of the lower energy protons (
eV). Error boxes larger than or equal to are most expected in
this case. On the other hand, in the case of heavy nuclei, the arrival
direction of the particles is strongly dependent on the coordinates of the
particle source. The deflection may be high enough () as to make
extremely difficult any identification of the sources unless the real magnetic
field configuration is accurately determined. Moreover, not every incoming
particle direction is allowed between a given source and the detector. This
generates sky patches which are virtually unobservable from the Earth. In the
particular case of the UHE events of Yakutsk, Fly's Eye, and Akeno, they come
from locations for which the deflection caused by the assumed magnetic field is
not significant.Comment: LaTeX + 2 postscript figures - Color versions of both figures (highly
recommended) available via anonymous ftp at
ftp://capc07.ast.cam.ac.uk/pub/uhecr_gmf as fig*.g
GZK Photons Above 10 EeV
We calculate the flux of "GZK-photons", namely the flux of photons produced
by extragalactic nucleons through the resonant photoproduction of pions, the so
called GZK effect. This flux depends on the UHECR spectrum on Earth, of the
spectrum of nucleons emitted at the sources, which we characterize by its slope
and maximum energy, on the distribution of sources and on the intervening
cosmological backgrounds, in particular the magnetic field and radio
backgrounds. For the first time we calculate the GZK photons produced by
nuclei. We calculate the possible range of the GZK photon fraction of the total
UHECR flux for the AGASA and the HiRes spectra. We find that for nucleons
produced at the sources it could be as large as a few % and as low as 10^{-4}
above 10 EeV. For nuclei produced at the sources the maximum photon fraction is
a factor of 2 to 3 times smaller above 10 EeV but the minimum could be much
smaller than for nucleons. We also comment on cosmogenic neutrino fluxes.Comment: 20 pages, 9 figures (21 panels), iopart.cls and iopart12.clo needed
to typese
Composition of UHECR and the Pierre Auger Observatory Spectrum
We fit the recently published Pierre Auger ultra-high energy cosmic ray
spectrum assuming that either nucleons or nuclei are emitted at the sources. We
consider the simplified cases of pure proton, or pure oxygen, or pure iron
injection. We perform an exhaustive scan in the source evolution factor, the
spectral index, the maximum energy of the source spectrum Z E_{max}, and the
minimum distance to the sources. We show that the Pierre Auger spectrum agrees
with any of the source compositions we assumed. For iron, in particular, there
are two distinct solutions with high and low E_{max} (e.g. 6.4 10^{20} eV and 2
10^{19} eV) respectively which could be distinguished by either a large
fraction or the near absence of proton primaries at the highest energies. We
raise the possibility that an iron dominated injected flux may be in line with
the latest composition measurement from the Pierre Auger Observatory where a
hint of heavy element dominance is seen.Comment: 19 pages, 6 figures (33 panels)- Uses iopart.cls and iopart12.clo- In
version 2: addition of a few sentences and two reference