180 research outputs found
Interactions of Cosmic Rays around the Universe. Models for UHECR data interpretation
Ultra high energy cosmic rays (UHECRs) are expected to be accelerated in
astrophysical sources and to travel through extragalactic space before hitting
the Earth atmosphere. They interact both with the environment in the source and
with the intergalactic photon fields they encounter, causing different
processes at various scales depending on the photon energy in the nucleus rest
frame. UHECR interactions are sensitive to uncertainties in the extragalactic
background spectrum and in the photo-disintegration models.Comment: 6 pages, 5 figure
Nuclear Physics Meets the Sources of the Ultra-High Energy Cosmic Rays
The determination of the injection composition of cosmic ray nuclei within
astrophysical sources requires sufficiently accurate descriptions of the source
physics and the propagation - apart from controlling astrophysical
uncertainties. We therefore study the implications of nuclear data and models
for cosmic ray astrophysics, which involves the photo-disintegration of nuclei
up to iron in astrophysical environments. We demonstrate that the impact of
nuclear model uncertainties is potentially larger in environments with
non-thermal radiation fields than in the cosmic microwave background. We also
study the impact of nuclear models on the nuclear cascade in a gamma-ray burst
radiation field, simulated at a level of complexity comparable to the most
precise cosmic ray propagation code. We conclude with an isotope chart
describing which information is in principle necessary to describe nuclear
interactions in cosmic ray sources and propagation.Comment: 11 pages, 6 figures. Publication is open acces
Cosmic-ray propagation in extragalactic space and secondary messengers
These notes summarize the lectures about "Cosmic-ray propagation in
extragalactic space and secondary messengers", focusing in particular on the
interactions of cosmic-ray particles with the background photons in the
Universe, including nuclear species heavier than hydrogen, and on the
analytical computation of the expected cosmic-ray fluxes at Earth. The lectures
were held at the Course 208 of the International School of Physics "Enrico
Fermi" on "Foundations of Cosmic-Ray Astrophysics", in Varenna (Como, Italy)
from June 23rd to June 29th, 2022. These notes are complementary to the content
of the lectures held by Pasquale Dario Serpico at the same school.Comment: 38 pages (including 3 appendices), 19 figures. To appear in
"Foundations of Cosmic Ray Astrophysics", Proceedings of the International
School of Physics "Enrico Fermi", Course 208, Varenna, 24 - 29 June 2022,
edited by F. Aharonian, E. Amato, and P. Blas
On the common origin of cosmic rays across the ankle and diffuse neutrinos at the highest energies from low-luminosity Gamma-Ray Bursts
We demonstrate that the UHECRs produced in the nuclear cascade in the jet of
Low-Luminosity Gamma-Ray Bursts (LL-GRBs) can describe the UHECR spectrum and
composition and, at the same time, the diffuse neutrino flux at the highest
energies. The radiation density in the source simultaneously controls the
neutrino production and the development of the nuclear cascade, leading to a
flux of nucleons and light nuclei describing even the cosmic-ray ankle at eV. The derived source parameters are consistent with
population studies, indicating a baryonic loading factor of about ten. Our
results motivate the continued experimental search of LL-GRBs as a unique GRB
population.Comment: 9 pages, 4 figure
Cosmic-Ray and Neutrino Emission from Gamma-Ray Bursts with a Nuclear Cascade
We discuss neutrino and cosmic-ray emission from Gamma-Ray Bursts (GRBs) with
the injection of nuclei, where we take into account that a nuclear cascade from
photo-disintegration can fully develop in the source. One of our main
objectives is to test if recent results from the IceCube and the Pierre Auger
Observatory can be accommodated with the paradigm that GRBs are the sources of
Ultra-High Energy Cosmic Rays (UHECRs). While our key results are obtained
using an internal shock model, we discuss how the secondary emission from a GRB
shell can be interpreted in terms of other astrophysical models. It is
demonstrated that the expected neutrino flux from GRBs weakly depends on the
injection composition, which implies that prompt neutrinos from GRBs can
efficiently test the GRB-UHECR paradigm even if the UHECRs are nuclei. We show
that the UHECR spectrum and composition, as measured by the Pierre Auger
Observatory, can be self-consistently reproduced in a combined
source-propagation model. In an attempt to describe the energy range including
the ankle, we find tension with the IceCube bounds from the GRB stacking
analyses. In an alternative scenario, where only the UHECRs beyond the ankle
originate from GRBs, the requirement for a joint description of cosmic-ray and
neutrino observations favors lower luminosities, which does not correspond to
the typical expectation from {\gamma}-ray observations.Comment: 36 pages, 25 figure
Cosmogenic Neutrinos Challenge the Cosmic Ray Proton Dip Model
The origin and composition of ultra-high-energy cosmic rays (UHECRs) remain a
mystery. The proton dip model describes their spectral shape in the energy
range above GeV by pair production and photohadronic interactions with
the cosmic microwave background. The photohadronic interactions also produce
cosmogenic neutrinos peaking around GeV. We test whether this model is
still viable in light of recent UHECR spectrum measurements from the Telescope
Array experiment, and upper limits on the cosmogenic neutrino flux from
IceCube. While two-parameter fits have been already presented, we perform a
full scan of the three main physical model parameters: source redshift
evolution, injected proton maximal energy, and spectral index. We find
qualitatively different conclusions compared to earlier two-parameter fits in
the literature: a mild preference for a maximal energy cutoff at the sources
instead of the Greisen--Zatsepin--Kuzmin (GZK) cutoff, hard injection spectra,
and strong source evolution. The predicted cosmogenic neutrino flux exceeds the
IceCube limit for any parameter combination. As a result, the proton dip model
is challenged at more than 95\% C.L. This is strong evidence against this model
independent of mass composition measurements.Comment: published in Apj; 15 pages, 12 figure
A new view on Auger data and cosmogenic neutrinos in light of different nuclear disintegration and air-shower models
We study the implications of Ultra-High Energy Cosmic Ray (UHECR) data from
the Pierre Auger Observatory for potential accelerator candidates and
cosmogenic neutrino fluxes for different combinations of nuclear disintegration
and air-shower models. We exploit the most recent spectral and mass composition
data (2017) with a new, computationally very efficient simulation code PriNCe.
We extend the systematic framework originally developed by the Pierre Auger
Collaboration with the cosmological source evolution as an additional free
parameter. In this framework, an ensemble of generalized UHECR accelerators is
characterized by a universal spectral index (equal for all injection species),
a maximal rigidity, and the normalizations for five nuclear element groups. We
find that the 2017 data favor a small but constrained contribution of heavy
elements (iron) at the source. We demonstrate that the results moderately
depend on the nuclear disintegration (PSB, Peanut, or Talys) model, and more
strongly on the air-shower (EPOS-LHC, Sibyll-2.3, or QGSjet-II-04) model.
Variations of these models result in different source evolutions and spectral
indices, limiting the interpretation in terms of a particular class of cosmic
accelerators. Better constrained parameters include the maximal rigidity and
the mass composition at the source. Hence, the cosmogenic neutrino flux can be
robustly predicted, since it originates from interactions with the cosmic
infrared background and peaks at . Depending on the
source evolution at high redshifts the flux is likely out of reach of future
neutrino observatories in most cases, and a minimal cosmogenic neutrino flux
cannot be claimed from data without assuming a cosmological distribution of the
sources.Comment: 21 pages, 11 figures. Accepted for publication in Ap
Binary Neutron Star Merger Remnants as Sources of Cosmic Rays Below the "Ankle"
We investigate non-thermal electron and nuclei energy losses within the
binary neutron star merger remnant produced by the event GW170817. The lack of
a cooling feature within the detected synchrotron emission from the source is
used to constrain the magnetic field at the mG level, assuming that this
emission is electron synchrotron in origin, and that the accelerated spectrum
in the electrons follows the form . The level of
subsequent gamma-ray emission from the source is demonstrated to provide a
further constraint on the source magnetic field strength. We also put forward
alternative strong (G) magnetic field scenarios able to support this
emission. For such stronger fields, the photo-disintegration of non-thermal
nuclei within the source is considered, and a bottleneck period of 5-30
days is found when this process peaks. We find that this class of source is in
principle able to support the population of cosmic rays detected at Earth below
the "ankle".Comment: Accepted for publication in Astropart. Phy
Astrophysical neutrino production and impact of associated uncertainties in photo-hadronic interactions of UHECRs
High energy neutrinos can be produced by interactions of ultra-high energy
cosmic rays (UHECRs) in the dense radiation fields of their sources as well as
off the cosmic backgrounds when they propagate through the universe.
Multi-messenger interpretations of current measurements deeply rely on the
understanding of these interactions. In order to efficiently produce neutrinos
in the sources of UHECRs, at least a moderate level of interactions is needed,
which means that a nuclear cascade develops if nuclei are involved. On the
other hand, the available cross-section data and interaction models turn out to
make poor predictions for most nuclei heavier than protons. We show the impact
of these uncertainties in state-of-the-art photo-disintegration models and
motivate nuclear cross-section measurements. Further, we discuss extensions for
photo-meson models currently used in astrophysics and demonstrate the
importance of understanding the details of UHECR interaction with the Glashow
resonance.Comment: invited talk presented at ISVHECRI 2018, submitted for publication to
EPJ Web of Conference
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