Ultra-high Energy Cosmic Ray Protons Research Articles

Propagation and fluxes of ultra-high energy cosmic rays in f(R)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varvec{f(R)}$$\\end{document} gravity theory

In this work, we study the effect of diffusion of ultra-high energy cosmic ray (UHECR) protons in the presence of turbulent magnetic fields (TMFs) in the light of the f(R) theory of gravity. The f(R) theory of gravity is a successful modified theory of gravity in explaining the various aspects of the observable Universe including its current state of expansion. For this work, we consider two most studied f(R) gravity models, viz., the power-law model and the Starobinsky model. With these two models, we study the diffusive character of the propagation of UHECR protons in terms of their density enhancement. The density enhancement is a measure of how the density of CRs changes due to their diffusion in the intergalactic medium and interaction with the cosmic microwave background (CMB) radiation. Ankle, instep and Greisen–Zatsepin–Kuzmin (GZK) cutoff are all spectrum characteristics that extragalactic UHECRs acquire when they propagate through the CMB. We analyse all these characteristics through the diffusive flux as well as its modification factor. Model dependence of the modification factor is minimal compared to the diffusive flux. We compare the UHECR proton spectra calculated for the considered f(R) gravity models with the available data of the Telescope Array (TA) and Pierre Auger Observatory (PAO). We see that both models of f(R) gravity predict energy spectra of UHECRs with all experimentally observed features, which lay well within the range of combined data of both experiments throughout the energy range of concern. It is to be noted that our present work is only to investigate the possible effects of f(R) gravity theory on the UHECRs propagation, using pure proton composition as a simplified case study since protons are least affected by magnetic fields. Hence, at this stage, our results cannot be used to favor or disfavor f(R) cosmology over Λ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Lambda $$\\end{document}CDM cosmology as more work is needed in this regard.

Production of high-energy neutrinos in binary-neutron-star merger events

High-energy neutral astrophysical messengers, such as neutrinos and photons, can be produced by the interaction of ultra-high-energy cosmic rays (UHECRs) with radiation fields, either during extragalactic propagation or within source environments. Neutrinos and gamma-rays can play a crucial role in the study of acceleration mechanisms of cosmic rays. In particular, after being produced, neutrinos leave the source environment and propagate to the Earth without further interactions. They are only subject to energy redshift and flavour oscillation, which makes them bearers of otherwise inaccessible information about their sources. We study high-energy environments of the type that are likely to be the end states of a binary-neutron-star (BNS) merger, and we model their local photon field as a black body at a given temperature. Using a modified version of the Monte Carlo code SimProp v2r4 we simulate the propagation and interaction of UHECRs through these environments. We consider several combinations for the spectral index and high-energy cutoff of the UHECR protons, in order to obtain the escaped neutrino flux. We propagate these fluxes to the Earth and compare to the astrophysical IceCube neutrino flux to obtain constraints on the BNS merger spectra properties, emissivity and density rate.

“Super GZK” Particles in a Classic Kramers’ Diffusion-over-a-barrier Model. I. The Case of Protons

Abstract In interactions of ultra-high-energy cosmic ray (UHECR) protons with cosmic microwave background photons, we focus in this work on photopion production reactions and the effects of the measured, broad, energy-loss distributions in these reactions on the evolution of the protons’ density functions in energy space. We rely on a Fokker–Planck transport equation in energy space whose transport coefficients are calculated using laboratory measurements. We also derive a Fokker–Planck potential that accounts for both systematic (drift) and stochastic (dispersive) energy losses due to photopion production reactions. Our results show that dispersive energy losses have significant effects on estimating the protons’ horizon distance and their energy spectrum, as well as to elucidate a broadness in the GZK cutoff. We use the derived Fokker–Planck potential to assign a characteristic probability for a proton to clear the potential barrier as a function of energy. This estimate of probability can be used to assist observations in distinguishing between protons and heavy ions as charged particles. Our model is able to account for the so-called super GZK particles as a classic diffusion-over-a-barrier manifestation of the transport of UHECR protons in energy space in quantifying the extent and broadness of the GZK cutoff.

Particle dynamics and GZK limit in relativity with a preferred frame

The theory termed ‘special relativity (SR) with a preferred frame’ incorporates the preferred frame into special relativity while retaining the fundamental space-time symmetry which, in the standard SR, manifests itself as Lorentz invariance. In this paper, the theory is extended to particle dynamics based on the concept of the ‘modified spacetime symmetry’ which allows to develop the theory along the lines of the standard relativity theory. The modified relativistic dynamics is applied to describing the interactions of the Ultra High Energy Cosmic Rays (UHECR) with universal diffuse background radiation and, in particular, to calculating the Greisen–Zatsepin–Kuzmin (GZK) threshold for the energy suppression due to pion photoproduction by UHECR protons. The result, that the GZK cutoff energy depends on the distance (cosmological redshift z) to the source of particles, may contribute to interpretation of the data on the mass composition of UHECR.

Ultrahigh-energy cosmic ray composition from the distribution of arrival directions

The sources of ultrahigh-energy cosmic rays (UHECRs) have been difficult to catch. It was recently pointed out that while sources of UHECR protons exhibit anisotropy patterns that become denser and compressed with rising energy, nucleus-emitting-sources give rise to a cepa stratis (onion-like) structure with layers that become more distant from the source position with rising energy. The peculiar shape of the hot spots from nucleus-accelerators is steered by the competition between energy loss during propagation and deflection on the Galactic magnetic field (GMF). Here, we run a full-blown simulation study to accurately characterize the deflections of UHECR nuclei in the GMF. We show that while the cepa stratis structure provides a global description of anisotropy patterns produced by UHECR nuclei en route to Earth, the hot spots are elongated depending on their location in the sky due to the regular structure of the GMF. We demonstrate that with a high-statistics sample at the high-energy-end of the spectrum, like the one to be collected by NASA's POEMMA mission, the energy dependence of the hot-spot contours could become a useful observable to identify the nuclear composition of UHECRs. This new method to determine the nature of the particle species is complementary to those using observables of extensive air showers, and therefore is unaffected by the large systematic uncertainties of hadronic interaction models.

ISOTROPY CONSTRAINTS ON POWERFUL SOURCES OF ULTRAHIGH-ENERGY COSMIC RAYS AT 1019 eV

ABSTRACT Anisotropy in the arrival direction distribution of ultrahigh-energy cosmic rays (UHECRs) produced by powerful sources is numerically evaluated. We show that nondetection of significant anisotropy at ≈ 10 19 ?> eV at present and in future experiments imposes general upper limits on UHECR proton luminosity of steady sources as a function of source redshifts. The upper limits constrain the existence of typical steady 10 19 ?> eV UHECR sources in the local universe and limit their local density to ≳ 10 − 3 ?> Mpc − 3 , ?> assuming average intergalactic magnetic fields less than 10 − 9 ?> G. This isotropy, being stronger than that measured at the highest energies, may indicate the transient generation of UHECRs. Our calculations are applied for extreme high-frequency-peaked BL Lacertae objects 1ES 0229+200, 1ES 1101–232, and 1ES 0347–121, to test the UHECR-induced cascade model, in which beamed UHECR protons generate TeV radiation in transit from sources. While the magnetic-field structure surrounding the sources affects the required absolute cosmic-ray luminosity of the blazars, the magnetic-field structure surrounding the Milky Way directly affects the observed anisotropy. If these magnetic fields are weak enough, significant UHECR anisotropy from these blazars is detectable by the Pierre Auger Observatory unless the maximum energy of UHECR protons is below 1019 eV. Furthermore, if these are the sources of UHECRs above 1019 eV, a local magnetic structure surrounding the Milky Way is needed to explain the observed isotropy at ∼ 10 19 ?> eV, which may be incompatible with large magnetic structures around all galaxies for the UHECR-induced cascade model to work with reasonable jet powers.

IceCube PeV cascade events initiated by electron-antineutrinos at Glashow resonance

We propose an interpretation of the two neutrino initiated cascade events with PeV energies observed by IceCube: Ultra-high energy cosmic ray protons (or Fe nuclei) scatter on CMB photons through the Delta-resonance (the Berezinsky-Zatsepin process) yielding charged pions and neutrons. The neutron decays give electron-antineutrinos which undergo neutrino oscillations to populate all antineutrino flavors, but the electron-antineutrino flux remains dominant. At 6.3 PeV electron-antineutrino energy their annihilation on electrons in the IceCube detector is enhanced by the Glashow resonance (the W-boson) whose decays can give the PeV showers observed in the IceCube detector. The two observed showers with ~1 PeV energies would need to be from W leptonic decays to electrons and taus. An order of magnitude higher event rate of showers at 6.3 PeV is predicted from W to hadron decays. This interpretation can be tested in the near term. It has significant physics implications on the origin of the highest energy cosmic rays, since neutrino events and cosmic ray events likely share a common origin.

Testing calculation results of Cherenkov radiation flux from extensive air showers using CORSIKA

This paper presents computational results of the spatiotemporal characteristics of Cherenkov light from particles of extensive air showers (EASs) induced by ultra-high-energy cosmic rays (UHECR). These results were obtained by simulating EAS events with the CORSIKA software package. Events were induced by UHECR particles, i.e., protons and iron nuclei with energies of 1015 and 1016 eV. The computational results were compared with experimental data obtained at the Yakutsk EAS array; possible causes of the discrepancy between them are discussed.

Restrictions on cosmogenic neutrinos and UHECR from Fermi 3 years data

Ultra-high energy cosmic ray protons accelerated in astrophysical objects produce secondary electromagnetic cascades during propagation in the cosmic microwave and infrared backgrounds. Those cascades contribute to the GeV-TeV diffuse photon flux, measured by Fermi LAT experiment. Recent studies of 3 years of Fermi LAT data have shown that diffuse gamma-ray background at E > 10GeV is about factor of 2 smaller then original one year data. This affects both models of UHECR and secondary cosmogenic neutrino fluxes. We show the allowed range of cosmogenic neutrino fluxes scanning over unknown UHECR parameters such as injected proton maximum energy and power law index, evolution of sources, systematic shift of UHECR energy scale. We consider three evolution models in which the UHECR sources are assumed to have the same evolution of either the star formation rate (SFR), or the gamma-ray burst (GRB) rate, or the active galactic nuclei (AGN) rate in the Universe and found that the last two are disfavored (and in the dip model rejected) by the new VHE gamma-ray background. We show that the largest fluxes predicted in the dip model would be detectable by IceCube in about 10 years of observation and are within the reach of a few years of observation with the ARA project. In the incomplete UHECR model in which protons are assumed to dominate only above 1019 eV, the cosmogenic neutrino fluxes could be a factor of 2 or 3 larger.

LOWER LIMITS ON ULTRAHIGH-ENERGY COSMIC RAY AND JET POWERS OF TeV BLAZARS

Lower limits on the power emitted in ultrahigh-energy cosmic rays (UHECRs), which are assumed to be protons with energy 1e17-1e20 eV, are derived for TeV blazars with the assumption that the observed TeV gamma rays are generated due to interactions of these protons with cosmic microwave photons. The limits depend on the spectrum of the injected UHECR protons. While for a -2.2 injection spectrum, the lower limits on the powers emitted in UHECRs by 1ES 0229+200, 1ES 1101-232 and 1ES 0347-121 are lower than their respective synchrotron luminosities (1e46 erg/s); in the case of 1ES 1426+428 it exceeds the corresponding synchrotron luminosity by up to an order of magnitude. The proposed Auger North Observatory should be able to detect 4e19 eV cosmic ray protons from 1ES 1426+428 within a few years of operation and test the TeV gamma-ray production model by UHECR energy losses while propagating along the line-of-sight, or constrain the intergalactic magnetic field to be larger than 1e-16 G in case of no detection. The lower limits on the apparent-isotropic jet power from accelerated 1e10-1e20 eV proton spectra in the blazar jet is of the order of the Eddington luminosity of a 1e9 solar mass black hole for a cosmic-ray injection spectrum -2.2 or harder for all blazars considered except for 1ES 1426+428. In the case of the latter the apparent-isotropic jet power exceeds the Eddington luminosity by an order of magnitude. For an injection spectrum softer than -2.2, as is required to fit the observed cosmic-ray data above 1e17-1e18 eV, the Eddington luminosity is exceeded by the lower limits on the jet power for all blazars considered.

Testing Lorentz invariance with neutrinos from ultrahigh energy cosmic ray interactions

We have previously shown that a very small amount of Lorentz invariance violation (LIV), which suppresses photomeson interactions of ultrahigh energy cosmic rays (UHECRs) with cosmic background radiation (CBR) photons, can produce a spectrum of cosmic rays that is consistent with that currently observed by the Pierre Auger Observatory (PAO) and HiRes experiments. Here, we calculate the corresponding flux of high energy neutrinos generated by the propagation of UHECR protons through the CBR in the presence of LIV. We find that LIV produces a reduction in the flux of the highest energy neutrinos and a reduction in the energy of the peak of the neutrino energy flux spectrum, both depending on the strength of the LIV. Thus, observations of the UHE neutrino spectrum provide a clear test for the existence and amount of LIV at the highest energies. We further discuss the ability of current and future proposed detectors make such observations.

Ultra-high-energy cosmic rays from black hole jets of radio galaxies

The Auger Collaboration reports (Auger Collaboration 2007 Science 318 939, The Pierre Auger Collaboration 2008 Astropart. Phys. 29 188) that the arrival directions of ≳60 EeV ultra-high-energy cosmic rays (UHECRs) cluster along the supergalactic plane and correlate with active galactic nuclei (AGN) within ≈ 100 Mpc. The association of several events with the nearby radio galaxy Centaurus A supports the paradigm that UHECRs are powered by supermassive black-hole engines and accelerated to ultra-high energies in the shocks formed by variable plasma winds in the inner jets of radio galaxies. The GZK horizon length of 75 EeV UHECR protons is ≈100 Mpc, so that the Auger results are consistent with an assumed proton composition of the UHECRs. In this scenario, the sources of UHECRs are FR II radio galaxies and FR I galaxies like Cen A with scattered radiation fields that enhance UHECR neutral-beam production. Radio galaxies with jets pointed away from us can still be observed as UHECR sources due to deflection of UHECRs by magnetic fields in the radio lobes of these galaxies. A broadband ∼1 MeV–10 EeV radiation component in the spectra of blazar AGN is formed by UHECR-induced cascade radiation in the extragalactic background light. This emission is too faint to be seen from Cen A, but could be detected from more luminous blazars.

Ultrahigh energy cosmic rays and the GeV-TeV diffuse gamma-ray flux

Ultra-high energy cosmic ray protons accelerated in astrophysical objects produce secondary electromagnetic cascades during propagation in the cosmic microwave and infrared backgrounds. We show that such cascades can contribute between ~1% and ~50% of the GeV-TeV diffuse photon flux measured by the EGRET experiment. The GLAST satellite should have a good chance to discover this flux.

Ultra high energy cosmic rays: Identification of possible sources, energy spectra, and propagation

This review is devoted to the problem of the origin of cosmic rays (CR) with energy E > 4 × 10 19 eV. The review mainly deals with the hypothesis of CR acceleration in active galactic nuclei (AGN). The review consists of the following five sections: Introduction, three chapters, and Conclusions. The following points are considered in Introduction: shower arrays for detecting ultra high energy cosmic rays (UHECR), the Greisen- Zatsepin-Kuzmin (GZK) cutoff, and the hypotheses of the UHECR origin. Since CRs are of extraterrestrial ori- gin, some astrophysical data used in CR physics are presented in a special section. The identification of UHECR sources with energies E > 4 × 10 19 eV is analyzed in Chapter 2. Chapter 3 deals with CR acceleration in sources and CR escape from sources. Chapter 4 is devoted to particle propagation in intergalactic space with allowance for CR interaction with the microwave background radiation and energy losses (blackbody or GZK cutoff). The propagation of UHECR protons is analyzed and their spectra at the Earth are calculated numerically. In Conclu- sions, we formulate the results and list the nuclear data needed to develop the model in more detail, namely, to study the propagation of CR nuclei in intergalactic space and to analyze the UHECR composition at the Earth.

Reconciling the ultra-high energy cosmic ray spectrum with Fermi shock acceleration

The energy spectrum of ultra-high energy cosmic rays (UHECR) is usually calculated for sources with identical properties. Assuming that all sources can accelerate UHECR protons to the same extremely high maximal energy Emax>1020 eV and have the steeply falling injection spectrum 1/E2.7, one can reproduce the measured cosmic ray flux above E≳1018 eV. We show that relaxing the assumption of identical sources and using a power-law distribution of their maximal energy allows one to explain the observed UHECR spectrum with the injection 1/E2.2 typically predicted by Fermi shock acceleration.

The impact of heavy nuclei on the cosmogenic neutrino flux

As ultra-high energy cosmic ray protons propagate through the universe, they undergo photo-meson interactions with the cosmic microwave background, generating the ‘cosmogenic’ neutrino flux. If, however, a substantial fraction of the cosmic ray primaries are heavy nuclei rather than protons, they would preferentially lose energy through photo-disintegration so the corresponding neutrino flux may be substantially depleted. We investigate this issue using a Monte Carlo simulation of cosmic ray propagation through intragalactic radiation fields and assess the impact of the altered neutrino fluxes on next-generation neutrino telescopes.