105 research outputs found
Extragalactic Sources and Propagation of UHECRs
With the publicly available astrophysical simulation framework for
propagating extraterrestrial UHE particles, CRPropa 3, it is now possible to
study realistic UHECR source scenarios including deflections in Galactic and
extragalactic magnetic fields in an efficient way. Here we discuss three recent
studies that have already been done in that direction. The first one
investigates what can be expected in the case of maximum allowed intergalactic
magnetic fields. Here is shown that, even if voids contain strong magnetic
fields, deflections of protons with energies from
nearby sources might be small enough to allow for UHECR astronomy. The second
study looks into several scenarios with a smaller magnetization focusing on
large-scale anisotropies. Here is shown that the local source distribution can
have a more significant effect on the large-scale anisotropy than the EGMF
model. A significant dipole component could, for instance, be explained by a
dominant source within 5 Mpc distance. The third study looks into whether
UHECRs can come from local radio galaxies. If this is the case it is difficult
to reproduce the observed low level of anisotropy. Therefore is concluded that
the magnetic field strength in voids in the EGMF model used here is too low
and/or there are additional sources of UHECRs that were not taken into account
in these simulations.Comment: UHECR2016 conference proceedin
PeV neutrinos from the propagation of ultra-high energy cosmic rays
We discuss the possibility that the PeV neutrinos recently observed by
IceCube are produced by the interactions of extragalactic cosmic rays during
their propagation through the radiation backgrounds. We show that the fluxes
resulting from the decays of neutrons produced in the interactions of cosmic
ray protons with the CMB background are suppressed (dd GeV/cm s sr), with those resulting from the decays of pions
produced in the interactions with the UV/optical/IR backgrounds being the
dominant ones at PeV energies. The anti-neutrino fluxes produced by the decay
of neutrons resulting from the photodisintegration of heavy nuclei with CMB
photons are also shown to be quite suppressed (dd GeV/cm s sr), while those produced by photo-pion processes with
UV/optical/IR backgrounds may be larger, although they are not expected to be
above those achievable in the pure proton case. Scenarios with mixed
composition and low cutoff rigidities can lead to PeV neutrino fluxes enhanced
with respect to those in the pure Fe scenarios. We also discuss the possible
impact of the Glashow resonance for the detection of these scenarios, showing
that it plays a moderate role.Comment: 14 pages, 4 figure
Cosmogenic gamma-rays and neutrinos constrain UHECR source models
We use CRPropa 3 to show how the expected cosmogenic neutrino and gamma-ray
spectra depend on the maximum energy of ultra-high energy cosmic rays (UHECRs)
at their sources, on the spectral index at injection and on the chemical
composition of UHECRs. The isotropic diffuse gamma-ray background measured by
Fermi/LAT is already close to touching upon a model with co-moving source
evolution and with the chemical composition, spectral index and maximum
acceleration energy optimized to provide the best fit to the UHECR spectrum and
composition measured by the Pierre Auger Collaboration. Additionally, the
detectable fraction of protons present at the highest energies in UHECRs, for
experiments with sensitivities to the single-flavor neutrino flux at
EeV in the range of - GeV cm s
sr, is shown as a function of the evolution of UHECR sources.
Experiments that reach this sensitivity will be able to significantly constrain
the proton fraction for realistic source evolution models.Comment: Proc. 35th ICRC, Busan, South Korea, PoS(ICRC2017)56
Targeting Earth: CRPropa learns to aim
Realistic predictions for the arrival directions of ultra-high-energy cosmic
rays require extensive simulations of UHECR propagation through 3D space,
potentially even including cosmological evolution and timing effects. Such 3D
or 4D simulations of cosmic-ray propagation suffer from the fact that a
relatively small target - the observer sphere - needs to be hit. If particles
are ejected in any direction from the source according to the source emission
geometry, such simulations are tremendously inefficient. We present here a
targeting mechanism which finds an optimal emission geometry to maximize the
number of hits while remaining unbiased in the arrival-direction distribution.
This can lead to speedups by many of orders of magnitude, depending on the
simulation setup. We present the basic mathematics to produce unbiased results
from targeted simulations, demonstrate its effectiveness with the simulation
package CRPropa 3 for various propagation scenarios, and discuss prospects to
include this mechanism as a standard part of CRPropa in the future.Comment: Presented at the 36th International Cosmic Ray Conference (ICRC 2019
Extragalactic magnetic field constraints from ultra-high-energy cosmic rays from local galaxies
We interpret the correlation between local star-forming galaxy positions and
ultra-high-energy cosmic ray (UHECR) directions, recently detected by the
Pierre Auger Observatory (PAO), in terms of physical parameters: the local
density of sources and the magnetic fields governing the UHECR propagation. We
include a Galactic magnetic field model on top of a random extragalactic
magnetic field description to determine the level of UHECR deflections expected
from an ensemble of source positions. Besides deflections in magnetic fields,
we also take into account energy losses with background photon fields as well
as spectrum and composition measurements by the PAO. We find consistency
between the PAO anisotropy measurement and the local star-forming galaxy
density for large extragalactic magnetic field strengths with (for a coherence length of ) at the confidence
level. Larger source densities lead to more isotropic background and
consequently allow for weaker extragalactic magnetic fields. However, the
acceleration of UHECR by such abundant sources is more challenging to motivate.
Too large source densities and extragalactic magnetic field strengths, on the
other hand, are also disfavored as that decreases the expected level of
anisotropy. This leads to upper limits of and at the 90\% confidence level.Comment: 10 pages, 6 figures, incl. appendices, accepted for publication in
MNRA
Cosmic ray propagation with CRPropa 3
Solving the question of the origin of ultra-high energy cosmic rays (UHECRs)
requires the development of detailed simulation tools in order to interpret the
experimental data and draw conclusions on the UHECR universe. CRPropa is a
public Monte Carlo code for the galactic and extragalactic propagation of
cosmic ray nuclei above eV, as well as their photon and neutrino
secondaries. In this contribution the new algorithms and features of CRPropa 3,
the next major release, are presented. CRPropa 3 introduces time-dependent
scenarios to include cosmic evolution in the presence of cosmic ray deflections
in magnetic fields. The usage of high resolution magnetic fields is facilitated
by shared memory parallelism, modulated fields and fields with heterogeneous
resolution. Galactic propagation is enabled through the implementation of
galactic magnetic field models, as well as an efficient forward propagation
technique through transformation matrices. To make use of the large Python
ecosystem in astrophysics CRPropa 3 can be steered and extended in Python.Comment: 16th International workshop on Advanced Computing and Analysis
Techniques in physics research (ACAT 2014) proceedings, 6 pages, 6 figure
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