Ultra-high Energy Cosmic Rays Data Research Articles

Constraints on the Hosts of UHECR Accelerators

Interactions of ultra-high-energy cosmic rays (UHECRs) in the surroundings of their accelerators can naturally explain the observed spectrum and composition of UHECRs, including the abundance of protons below the ankle. Here we show that astrophysical properties of the UHECR source environment such as the temperature, size, and magnetic field can be constrained by UHECR and neutrino data. Applying this to candidate sources with a simple structure shows that starburst galaxies are consistent with these constraints, but galaxy clusters are in tension with them. For multicomponent systems like active galactic nuclei and gamma-ray bursts, the results are indicative, but a customized analysis is needed for definitive conclusions.

Ultra-High-Energy Cosmic Rays from a Population of Non-identical Sources

Astrophysical candidates for the sources of ultra-high-energy cosmic rays (UHECRs) exhibit a large diversity in terms of their properties relevant for the acceleration of charged particles, such as luminosity, Lorentz factor, size and magnetic field. Yet, fits of the observed UHECR spectrum and composition often assume identical sources. Here we investigate a population of sources with a power-law distribution of maximum energies. We show that the allowed source-to-source variance of the maximum energy must be small to describe the UHECR data. Even in the most extreme scenario, with a very sharp cutoff of individual source spectra and negative redshift evolution of the accelerators, the maximum energies of 90% of sources must be identical within a factor of three – in contrast to the variance expected for astrophysical sources. However, the overall population variance can be large when maximum rigidities are distributed as a broken power law, with a steep decline above the break and with hard source spectra. In this scenario, most of the observed UHECR flux is produced by sources near the break.

Observational Constraints on Cosmic-Ray Escape from Ultrahigh-energy Accelerators

Interactions of ultra-high energy cosmic rays (UHECRs) accelerated in specific astrophysical environments have been shown to shape the energy production rate of nuclei differently from that of the secondary neutrons escaping from the confinement zone. Here, we aim at testing a generic scenario of in-source interactions through phenomenological modeling of the flux and composition of UHECRs. We fit a model in which nucleons and nuclei follow different particle energy distributions to the all-particle energy spectrum and proton spectrum below the ankle energy and distributions of maximum shower depths above this energy, as inferred at the Pierre Auger Observatory. We obtain that the data can be reproduced using a spatial distribution of sources that follows the density of extragalactic matter on both local and large scales, providing hence a realistic set of constraints for the emission mechanisms in cosmic accelerators, for their energetics, and for the abundances of elements at escape from their environments. While the quasi monoelemental increase of the cosmic-ray mass number observed on Earth from ≃2 EeV up to the highest energies calls for nuclei accelerated with a hard spectral index, the inferred flux of protons down to ≃0.6 EeV is shown to require for this population a spectral index significantly softer than that generally obtained up to now. We demonstrate that modeling UHECR data across the ankle substantiates the conjecture of in-source interactions in a robust statistical framework, although pushing the mechanism to the extreme.

Search for Spatial Correlations of Neutrinos with Ultra-high-energy Cosmic Rays

For several decades, the origin of ultra-high-energy cosmic rays (UHECRs) has been an unsolved question of high-energy astrophysics. One approach for solving this puzzle is to correlate UHECRs with high-energy neutrinos, since neutrinos are a direct probe of hadronic interactions of cosmic rays and are not deflected by magnetic fields. In this paper, we present three different approaches for correlating the arrival directions of neutrinos with the arrival directions of UHECRs. The neutrino data are provided by the IceCube Neutrino Observatory and ANTARES, while the UHECR data with energies above ∼50 EeV are provided by the Pierre Auger Observatory and the Telescope Array. All experiments provide increased statistics and improved reconstructions with respect to our previous results reported in 2015. The first analysis uses a high-statistics neutrino sample optimized for point-source searches to search for excesses of neutrino clustering in the vicinity of UHECR directions. The second analysis searches for an excess of UHECRs in the direction of the highest-energy neutrinos. The third analysis searches for an excess of pairs of UHECRs and highest-energy neutrinos on different angular scales. None of the analyses have found a significant excess, and previously reported overfluctuations are reduced in significance. Based on these results, we further constrain the neutrino flux spatially correlated with UHECRs.

Northern Hemisphere UHECR data further supports CMBR photons with weak U(1) component

I further test the theory that the Cosmic Background Radiation (CBR) is made of photons with a weak U(1) component. Tipler (2005) has previously argued that the consistency of the Standard Model (SM) with the Second Law of Thermodynamics requires the early universe CBR to be composed mainly of an SU(2) gauge field. The U(1) field would be suppressed. One of the consequences of this approach is that the Ultra High Energy Cosmic Rays (UHECR) would be able to propagate much further than conventionally accepted, as an SU(2) dominant CBR would be largely unable to couple with right handed fermions. I test if this novel theory solves the problem of UHECR origin by finding suitable candidates up to a redshift z = 0.1 within three degrees of the arrival direction. Utilizing the Fly's Eye Northern Hemisphere UHECR data, I identified candidates with 80% success for the Northern Sky UHECR (98.7% if certain celestial objects which are likely to be Active Galactic Nuclei are absolutely identified as such). This is parsimonious with the CBR theory, which has other important implications for the Standard Model, early universe cosmology, and the origin of matter and anti-matter. This builds off of Tipler and Piasecki (2018), where we have reviewed UHECR data from the Southern Hemisphere to get a 86% success identification rate. We predict that the remaining UHECR not paired with a potential source will have sources identified upon closer telescopic investigations of these regions. Other recent experiments further suggest an SU(2) dominant composition of the CBR photons. The problem of UHECR origin may be solved.

Systematic parameter space study for the UHECR origin from GRBs in models with multiple internal shocks

ABSTRACT We scrutinize the paradigm that conventional long-duration gamma-ray bursts (GRBs) are the dominant source of the ultrahigh energy cosmic rays (UHECRs) within the internal shock scenario by describing UHECR spectrum and composition and by studying the predicted (source and cosmogenic) neutrino fluxes. Since it has been demonstrated that the stacking searches for astrophysical GRB neutrinos strongly constrain the parameter space in single-zone models, we focus on the dynamics of multiple collisions for which different messengers are expected to come from different regions of the same object. We propose a model that can describe both stochastic and deterministic engines, which we study in a systematic way. We find that GRBs can indeed describe the UHECRs for a wide range of different model assumptions with comparable quality albeit with the previously known problematic energy requirements; the heavy mass fraction at injection is found to be larger than 70 per cent ($95 {{\ \rm per\ cent}}$ CL). We demonstrate that the post-dicted (from UHECR data) neutrino fluxes from sources and UHECR propagation are indeed below the current sensitivities but will be reached by the next generation of experiments. We finally critically review the required source energetics with the specific examples found in this study.

Galactic magnetic field bias on inferences from UHECR data

A consequence of Liouville's theorem indicates that the recently observed large scale anisotropy in the arrival direction of Ultra-High-Energy Cosmic Rays (UHECRs) cannot be produced from an isotropic extragalactic flux, thus some anisotropy already needs to be present outside our Galaxy. But in this case, the observed spectrum and composition of UHECRs differ from the one outside of the Milky Way, due to the suppression or the amplification of the UHECR flux from certain directions by the Galactic magnetic field. In this work, we investigate this effect for the case of a dipole and a quadrupole anisotropy, respectively, for the widely-used JF12 and PT11 magnetic field models. We investigate bounds on the maximal amplitude of the observed anisotropy and the maximal charge number of UHECRs. Furthermore, the flux modification is discussed in the light of the recent Auger results about the dipolar anisotropy and the mass composition. We find that this effect yields a modification of the observed flux of up to ∼ 25% for the investigated magnetic field model and the observed dipole, in particular for a heavy chemical composition of UHECRs as suggested by Auger data interpreted assuming the `Sibyll2.3c' or the `EPOS-LHC' model of hadronic interactions in air showers.

High energy interactions of cosmic rays

A discussion of a number of important topics related to modeling of high energy cosmic ray interactions is presented. Special attention is devoted to novel theoretical approaches employed in event generators of hadronic interactions and to the impact of experimental data from the Large Hadron Collider (LHC). In relation to studies of ultra-high energy cosmic rays (UHECRs), differences between various predictions for basic characteristics of UHECR-induced extensive air showers in the atmosphere are analyzed and traced down to differences in the respective treatments of hadronic interactions. Possibilities to discriminate between the alternative approaches, based on LHC and UHECR data, are demonstrated and the relation to UHECR primary composition is outlined. Finally, in relation to direct studies of charged cosmic rays, potential improvements of the treatment of cosmic ray interactions at low and intermediate energies are discussed.

What can we learn if we try to account for the all-sky UHECR data?

I examine the question of the origin of the Ultrahigh Energy Cosmic Rays (UHECRs) in the light of the data available at the highest energies.

Limits on the Lorentz Invariance Violation from UHECR Astrophysics

Abstract In this paper, the Lorentz invariance violation (LIV) is introduced in the calculations of photon propagation in the universe. LIV is considered in the photon sector, and the mean-free path of the interaction is calculated. The corresponding photon horizon, including LIV effects, is used to predict major changes in the propagation of photons with energy above 1018 eV. The flux of GZK photons on Earth, considering LIV, is calculated for several source models of ultra-high-energy cosmic rays (UHECRs). The predicted flux of GZK gamma-rays is compared to the new upper limits on the photon flux obtained by the Pierre Auger Observatory in order to impose upper limits on the LIV coefficients of order n = 0, 1, and 2. The limits on the LIV coefficients derived here are more realistic than previous works and in some cases more restrictive. The analysis resulted in LIV upper limits in the photon sector of , , and in the astrophysical scenario, which best describes UHECR data.

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.

Erratum: Testing the newborn pulsar origin of ultrahigh energy cosmic rays with EeV neutrinos [Phys. Rev. D90, 103005 (2014)

Fast-spinning newborn pulsars are intriguing candidate sources of ultrahigh energy cosmic rays (UHECRs). The acceleration of particles with a given composition in a fraction of the extragalactic pulsar population can give a consistent explanation for the measurements of the Auger Observatory. We calculate the associated diffuse neutrino flux produced while particles cross the supernova ejecta surrounding the stars. We show that in the minimal pulsar scenario that are compatible with the UHECR data, the effective optical depth to hadronuclear interactions is larger than unity at ultrahigh energies. Thus, even in the most pessimistic case, one expects energy fluxes of $\sim 0.1 - 1 \,\rm EeV$ neutrinos that should be detectable with IceCube or Askaryan Radio Array within a decade.

Testing the newborn pulsar origin of ultrahigh energy cosmic rays with EeV neutrinos

Fast-spinning newborn pulsars are intriguing candidate sources of ultrahigh-energy cosmic rays (UHECRs). The acceleration of particles with a given composition in a fraction of the extragalactic pulsar population can give a consistent explanation for the measurements of the Auger Observatory. We calculate the associated diffuse neutrino flux produced while particles cross the supernova ejecta surrounding the stars. We show that in the minimal pulsar scenarios that are compatible with the UHECR data, the effective optical depth to hadronuclear interactions is larger than unity at ultrahigh energies. Thus, even in the most pessimistic case, one expects energy fluxes of $\ensuremath{\sim}0.1--1\text{ }\text{ }\mathrm{EeV}$ neutrinos that should be detectable with IceCube or the Askaryan Radio Array within a decade.

A Bayesian self-clustering analysis of the highest energy cosmic rays detected by the Pierre Auger Observatory

Cosmic rays (CRs) are protons and atomic nuclei that flow into our Solar system and reach the Earth with energies of up to ~10^21 eV. The sources of ultra-high energy cosmic rays (UHECRs) with E >~ 10^19 eV remain unknown, although there are theoretical reasons to think that at least some come from active galactic nuclei (AGNs). One way to assess the different hypotheses is by analysing the arrival directions of UHECRs, in particular their self-clustering. We have developed a fully Bayesian approach to analyzing the self-clustering of points on the sphere, which we apply to the UHECR arrival directions. The analysis is based on a multi-step approach that enables the application of Bayesian model comparison to cases with weak prior information. We have applied this approach to the 69 highest energy events recorded by the Pierre Auger Observatory (PAO), which is the largest current UHECR data set. We do not detect self-clustering, but simulations show that this is consistent with the AGN-sourced model for a data set of this size. Data sets of several hundred UHECRs would be sufficient to detect clustering in the AGN model. Samples of this magnitude are expected to be produced by future experiments, such as the Japanese Experiment Module Extreme Universe Space Observatory (JEM-EUSO).

High-energy cosmic rays and tests of basic principles of Physics

With the present understanding of data, the observed flux suppression for ultra-high energy cosmic rays (UHECR) at energies above 4.10E19 eV can be a signature of the Greisen-Zatsepin-Kuzmin (GZK) cutoff or be related to a similar mechanism. But it may also correspond, for instance, to the maximum energies available at the relevant sources. In both cases, violations of special relativity modifying cosmic-ray propagation or acceleration at very high energy can potentially play a role. Other violations of fundamental principles of standard particle physics (quantum mechanics, energy and momentum conservation, homogeneity and static properties, effective space dimensions, quark confinement...) can also be relevant at these energies. In particular, UHECR data would in principle allow to set bounds on Lorentz symmetry violation (LSV) in patterns incorporating a privileged local reference frame (the vacuum rest frame, VRF). But the precise analysis is far from trivial, and other effects can also be present. The effective parameters can be related to Planck-scale physics, or even to physics beyond Planck scale, as well as to the dynamics and effective symmetries of LSV for nucleons, quarks, leptons and the photon. LSV can also be at the origin of GZK-like effects. In the presence of a VRF, and contrary to a grand unification view, LSV and other violations of standard principles can modify the internal structure of particles at very high energy and conventional symmetries may cease to be valid at energies close to the Planck scale. We present an updated discussion of these topics, including experimental prospects, new potentialities for high-energy cosmic ray phenomenology and the possible link with unconventional pre-Big Bang scenarios, superbradyon (superluminal preon) patterns... The subject of a possible superluminal propagation of neutrinos at accelerator energies is also dealt with. (Contribution to the International Conference on New Frontiers in Physics, ICFP 2012, Kolymbari, Crete, June 10-16 2012)

Ultra-high energy physics and standard basic principles

It has not yet been elucidated whether the observed flux suppression for ultra- high energy cosmic rays (UHECR) at energies above � 4x1 0 19 eV is a signature of the Greisen-Zatsepin-Kuzmin (GZK) cutoff or a consequence of other phenomena. In both cases, violations of the standard fundamental principles of Physics can be present and play a significant role. They can in particular modify cosmic-ray interactions, prop- agation or acceleration at very high energy. Thus, in a long-term program, UHECR data can hopefully be used to test relativity, quantum mechanics, energy and momentum con- servation, properties... as well as the elementariness of standard particles. Data on cosmic rays at energies � 10 20 eV may also be sensitive to new physics generated well beyond Planck scale. A typical example is provided by the search for possible sig- natures of a Lorentz symmetry violation (LSV) associated to a privileged local reference frame (the vacuum rest frame, VRF). If a VRF exists, the internal structure of standard particles at ultra-high energy can undergo substantial modifications. Similarly, the con- ventional particle symmetries may cease to be valid at such energies instead of heading to a grand unification and the structure of may no longer be governed by standard quantum field theory. Then, the question whether the notion of Planck scale still makes sense clearly becomes relevant and the very grounds of Cosmology can undergo essential modifications. UHECR studies naturally interact with the interpretation of WMAP and Planck observations. Recent Planck data analyses tend to confirm the possible existence of a privileged space direction. If the observed phenomenon turns out to be a signature of the spinorial space-time (SST) we suggested in 1996-97, then conventional Particle Physics may correspond to the local properties of standard matter at low enough energy and large enough distances. This would clearly strengthen the cosmological relevance of UHECR phenomenology and weaken the status of the Planck scale hypothesis. Another crucial observation is that, already before incorporating standard matter and relativity, the SST geometry naturally yields a Ht = 1 law where t is the age of the Universe and H the ratio between relative speeds and distances at cosmic scale. As standard cosmology is not required to get such a fundamental result, the need for a conventional Planck scale is far from obvious and the study of UHECR can potentially yield evidence for an alter- native approach including new physics and new ultimate constituents of matter. UHECR may in particular allow to explore the possible indications of the existence of a transition scale at very high energy where the standard laws would start becoming less and less dominant and new physics would replace the conventional fundamental principles. We discuss prospects of searches for potential signatures of such a phenomenon.

Correlation between ultra-high-energy cosmic rays and active galactic nuclei from the fermi large-area telescope

We study the possibility that the $\gamma$-ray loud active galactic nuclei (AGN) are the sources of ultra-high energy cosmic rays (UHECR), through the correlation analysis of their locations and the arrival directions of UHECR. We use the $\gamma$-ray loud AGN with $d\le 100 {\rm Mpc}$ from the second Fermi Large Area Telescope AGN catalog and the UHECR data with $E\ge 55 {\rm EeV}$ observed by Pierre Auger Observatory. The distribution of arrival directions expected from the $\gamma$-ray loud AGN is compared with that of the observed UHECR using the correlational angular distance distribution and the Kolmogorov-Smirnov test. We conclude that the hypothesis that the $\gamma$-ray loud AGN are the dominant sources of UHECR is disfavored unless there is a large smearing effect due to the intergalactic magnetic fields.

DO ULTRAHIGH ENERGY COSMIC RAYS COME FROM ACTIVE GALACTIC NUCLEI ANDFERMIγ-RAY SOURCES?

We study possible correlations between ultrahigh energy cosmic rays (UHECRs), observed by Auger, AGASA and Yakutsk, and nearby active galactic nuclei (AGNs) and $Fermi$ sources. We consider the deflection effects by a Galactic magnetic field (GMF) model constrained by the most updated measurements. We found that the average deflection angles of UHECRs by the Galactic magnetic fields are less than $4^\circ$. A correlation between the Auger cosmic-ray events and nearby AGNs with a significance level of $\sim 4\sigma$ was found for the Auger UHECR data sets with or without deflection correction. No correlation was found between the AGASA/Yakutsk events with nearby AGNs. Marginal correlations between the Auger events and the $Fermi$ sources, and between AGASA events and $Fermi$ AGNs were found when the deflections calculated by the GMF model were considered. However, no correlation was found between the Yakutsk data and $Fermi$ sources. Some $Fermi$ sources are close to the arrival directions of UHECR events detected by Auger, AGASA, and Yakutsk, most of which are probably chance coincidence rather than objects producing UHECRs in the nearby Universe. Four $Fermi$ sources, NGC 4945, ESO 323-G77, NGC 6951, and Cen A, within 100~Mpc have UHECR events within $3.1^{\circ}$ from their positions, which could potentially be cosmic ray accelerators. However, the association can only be confirmed if more UHECRs are preferably detected in these directions.

Lorentz invariance violation and the observed spectrum of ultrahigh energy cosmic rays

There has been much interest in possible violations of Lorentz invariance, particularly motivated by quantum gravity theories. It has been suggested that a small amount of Lorentz invariance violation (LIV) could turn off photomeson interactions of ultrahigh energy cosmic rays (UHECRs) with photons of the cosmic background radiation and thereby eliminate the resulting sharp steepening in the spectrum of the highest energy CRs predicted by Greisen Zatsepin and Kuzmin (GZK). Recent measurements of the UHECR spectrum reported by the HiRes and Auger collaborations, however, indicate the presence of the GZK effect. We present the results of a detailed calculation of the modification of the UHECR spectrum caused by LIV using the formalism of Coleman and Glashow. We then compare these results with the experimental UHECR data from Auger and HiRes. Based on these data, we find a best-fit amount of LIV of 4.5 - 4.5 + 1.5 × 10 - 23 , consistent with an upper limit of 6 × 10 - 23 . This possible amount of LIV can lead to a recovery of the cosmic ray spectrum at higher energies than presently observed. Such an LIV recovery effect can be tested observationally using future detectors.

On the origin of ultra high energy cosmic rays: subluminal and superluminal relativistic shocks

Aims. The flux of ultra high energy cosmic rays (UHECRs) at E > 10 18.5 eV is believed to arise in plasma shock environments in extragalactic sources. In this paper, we present a systematic study of cosmic ray (CR) particle acceleration by relativistic shocks, in particular concerning the dependence on bulk Lorentz factor and the angle between the magnetic field and the shock flow. The contribution to the observed diffuse CR spectrum provided by the accelerated particles is discussed. Methods. For the first time, Monte Carlo simulations for super- and subluminal shocks are extended to boost factors up to Γ= 1000 and systematically compared. The source spectra derived are translated into the expected diffuse proton flux from astrophysical sources by folding the spectra with the spatial distribution of active galactic nuclei (AGN) and gamma ray bursts (GRBs). Results of these predictions are compared with UHECR data. Results. While superluminal shocks are shown to be inefficient at providing acceleration to the highest energies (E > 10 18.5 eV), subluminal shocks may provide particles up to 10 21 eV, limited only by the Hillas-criterion. In the subluminal case, we find that mildly-relativistic shocks, thought to occur in jets of AGN (Γ ∼ 10−30), yield energy spectra of dN/dE ∼ E −2 . Highly relativistic shocks expected in GRBs (100 < Γ < 1000), on the other hand, produce spectra as flat as ∼E −1.0 above 10 9.5 GeV. The model results are compared with the measured flux of CRs at the highest energies and it is shown that, while AGN spectra provide an excellent fit, GRB spectra are too flat to explain the observed flux. The first evidence of a correlation between the CR flux above 5.7 × 10 10 GeV and the distribution of AGN provided by Auger are explained by our model. Although GRBs are excluded as the principle origin of UHECRs, neutrino production is expected in these sources either in mildly or highly relativistic shocks. In particular, superluminal shocks in GRBs may be observable via neutrino and photon fluxes, rather than as protons.