Observation of Fine Time Structures in the Cosmic Proton and Helium Fluxes with the Alpha Magnetic Spectrometer on the International Space Station
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79 ASTRONOMY AND ASTROPHYSICS↗
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Measurement of the cosmic ray proton spectrum from 40 GeV to 100 TeV with the DAMPE satellite
The precise measurement of the spectrum of protons, the most abundant component of the cosmic radiation, is essential to understand the source and acceleration of cosmic rays in the Milky Way. This work reports the measurement of the cosmic ray proton fluxes with kinetic energies from 40 GeV to 100 TeV, with 2 1 / 2 years of data recorded by the DArk Matter Particle Explorer (DAMPE). This is the first time that an experiment directly measures the cosmic ray protons up to ~100 TeV with high statistics. The measured spectrum validates the spectral hardening at ~300 GeV found by previous experiments and reveals a softening at ~13.6 TeV, with the spectral index changing from ~2.60 to ~2.85. Our result implies the existence of a new spectral feature of cosmic rays at energies lower than the so-called knee and sheds new light on the origin of Galactic cosmic rays.
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Tungsten fragmentation in nuclear reactions induced by high-energy cosmic-ray protons
Tungsten fragmentation arising in nuclear reactions induced by cosmic-ray protons in space-vehicle electronics is considered. In modern technologies of integrated circuits featuring a three-dimensional layered architecture, tungsten is frequently used as a material for interlayer conducting connections. Within the preequilibrium model, tungsten-fragmentation features, including the cross sections for the elastic and inelastic scattering of protons of energy between 30 and 240 MeV; the yields of isotopes and isobars; their energy, charge, and mass distributions; and recoil energy spectra, are calculated on the basis of the TALYS and EMPIRE-II-19 codes. It is shown that tungsten fragmentation affects substantially forecasts of failures of space-vehicle electronics.
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Explanation of the spectral hardening of relativistic galactic cosmic-ray protons
The transport of Galactic cosmic rays is investigated in the energy range of 70 GeV⩽E⩽10{sup 6} GeV including the newly calculated proton loss rate due to pion production. The break in the energy loss rate at about 200 GeV leads to a hardening from low to high energies in the differential number density of about ∼E{sup 0.1}. This break is confirmed by measurements of different cosmic-ray experiments.
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MEASUREMENTS OF COSMIC-RAY PROTON AND HELIUM SPECTRA FROM THE BESS-POLAR LONG-DURATION BALLOON FLIGHTS OVER ANTARCTICA
The BESS-Polar Collaboration measured the energy spectra of cosmic-ray protons and helium during two long-duration balloon flights over Antarctica in 2004 December and 2007 December at substantially different levels of solar modulation. Proton and helium spectra probe the origin and propagation history of cosmic rays in the galaxy, and are essential to calculations of the expected spectra of cosmic-ray antiprotons, positrons, and electrons from interactions of primary cosmic-ray nuclei with the interstellar gas, and to calculations of atmospheric muons and neutrinos. We report absolute spectra at the top of the atmosphere for cosmic-ray protons in the kinetic energy range 0.2–160 GeV and helium nuclei in the range 0.15–80 GeV/nucleon. The corresponding magnetic-rigidity ranges are 0.6–160 GV for protons and 1.1–160 GV for helium. These spectra are compared to measurements from previous BESS flights and from ATIC-2, PAMELA, and AMS-02. We also report the ratio of the proton and helium fluxes from 1.1 to 160 GV and compare this to the ratios from PAMELA and AMS-02.
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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 10{sup 9} GeV by pair production and photohadronic interactions with the cosmic microwave background. The photohadronic interactions also produce cosmogenic neutrinos peaking around 10{sup 9} 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 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.
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On the origin of a kink in the hardness spectra of cosmic-ray protons and helium nuclei in the vicinity of 230 GV
A three-component phenomenological model for the description of specific features of spectra of cosmic-ray protons and helium nuclei in the hardness range from 30 to 2 × 10{sup 5} GV is proposed. The first component corresponds to the constant background; the second component, to a variable “soft” (30–500 GV) heliospheric source; and the third component, to a variable “hard” (0.5–200 TV) galactic source inside a local bubble. The corresponding “surfatron accelerators” are responsible for the existence and variability of both sources. In order for such accelerators to operate, there should be an extended area with a nearly uniform and constant (in both the magnitude and direction) magnetic field and electromagnetic waves propagating perpendicular (or obliquely) to it. The dimensions of each source determine the maximum energy to which cosmic rays can be accelerated. The soft source with a size of ∼100 au lies at the periphery of the heliosphere, beyond the terminal shock, while the hard source with a size of >0.1 pc is located near the boundary of a local interstellar cloud at a distance of ∼0.01 pc from the Sun. A kink in the hardness spectra of p and He (near the hardness of about 230 GV) is caused by the variability of physical conditions in the acceleration region and depends on the relation between the amplitudes and power-law indices of the background, the soft heliospheric source, and the nearby hard galactic source. Ultrarelativistic acceleration of p and He in space plasma by an electromagnetic wave propagating perpendicular to the external magnetic field is investigated using numerical calculations. The conditions for particle trapping by the wave, as well as the dynamics of the velocity and momentum components, are analyzed. The calculations show that, in contrast to electrons and positrons (e{sup +}), a trapped proton can escape from the effective potential well after a relatively short time, thereby terminating to accelerate. Such an effect gives rise to softer spectra of p and He sources as compared to those of e{sup +}. The possibility of deviation of the spectra of accelerated protons from standard power-law dependences due to the surfatron mechanism is discussed.
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On the reason for the kink in the rigidity spectra of cosmic-ray protons and helium nuclei near 230 GV
A three-component phenomenological model describing the specific features of the spectrum of cosmic-ray protons and helium nuclei in the rigidity range of 30–2×10{sup 5} GV is proposed. The first component corresponds to the constant background; the second, to the variable “soft” (30–500 GV) heliospheric source; and the third, to the variable “hard” (0.5–200 TV) source located inside a local bubble. The existence and variability of both sources are provided by the corresponding “surfatron accelerators,” whose operation requires the presence of an extended region with an almost uniform (in both magnitude and direction) magnetic field, orthogonally (or obliquely) to which electromagnetic waves propagate. The maximum energy to which cosmic rays can be accelerated is determined by the source size. The soft source with a size of ∼100 AU is located at the periphery of the heliosphere, behind the front of the solar wind shock wave. The hard source with a size of >0.1 pc is located near the boundary of an interstellar cloud at a distance of ∼0.01 pc from the Sun. The presence of a kink in the rigidity spectra of p and He near 230 GV is related to the variability of the physical conditions in the acceleration region and depends on the relation between the amplitudes and power-law exponents in the dependences of the background, soft heliospheric source, and hard near galactic source. The ultrarelativistic acceleration of p and He by an electromagnetic wave propagating in space plasma across the external magnetic field is numerically analyzed. Conditions for particle trapping by the wave and the dynamics of the particle velocity and momentum components are considered. The calculations show that, in contrast to electrons and positrons (e{sup +}), the trapped protons relatively rapidly escape from the effective potential well and cease to accelerate. Due to this effect, the p and He spectra are softer than that of e{sup +}. The possibility that the spectra of accelerated protons deviate from standard power-law dependences due to the surfatron mechanism is discussed.
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Data release for A search for extremely-high-energy neutrinos and first constraints on the ultra-high-energy cosmic-ray proton fraction with IceCube
<h1 id="summary">Summary</h1> <p>Title: Data Release for A search for extremely-high-energy neutrinos and first constraints on the ultra-high-energy cosmic-ray proton fraction with IceCube</p> <p>The IceCube observatory analyzed 12.6 years of data in search of extremely-high-energy (EHE) neutrinos above 5 PeV. The resultant limit of the search (Fig 1), and the effective area of the event selection (Fig 7), are provided in this data release.</p> <h1 id="contents">Contents</h1> <ul> <li><p>README file: this file</p> </li> <li><p><code>differential_limit_and_sensitivity.csv</code>: a comma separated value file, giving the observed experimental differential limit, and sensitivity, of the search as a function of neutrino energy. This is the content of Fig 1 in the paper. The first column is the neutrino energy in GeV. The second column is the limit in units of GeV/cm2/s/sr. The third column is the sensitivity in units of GeV/cm2/s/sr.</p> </li> <li><p><code>effective_area.csv</code>: a comma separated value file, giving the effective area of the search as a function of energy. This is the content of Fig 7 in the paper. The first column is the neutrino energy in GeV. The second column is the total effective area of the search, summed across neutrino flavors, and averaged across neutrinos and antineutrinos, in meters-squared. The third column is the effective area of the search for the average of electron neutrino and electron antineutrinos in units of meters-squared. The fourth column is the same as the third, but for muon-flavor neutrinos. The fifth column is the same as the third and fourth, but for tau-flavor neutrinos.</p> </li> <li><p><code>demo.py</code>: a short python script to demonstrate how to read the files. Run like <code>python demo.py</code>. A standard base python installation is sufficient, as the only dependencies are numpy and matplotlib.</p> </li> </ul> <h1 id="contacts">Contacts</h1> <p>For any questions about this data release, please write to analysis@icecube.wisc.edu</p>
Astronomy and Astrophysics↗
Search for Extremely-High-Energy Neutrinos and First Constraints on the Ultrahigh-Energy Cosmic-Ray Proton Fraction with IceCube
Here, we present a search for the diffuse extremely-high-energy neutrino flux using 12.6 years of IceCube data. The nonobservation of neutrinos with energies well above 10 PeV constrains the all-flavor neutrino flux at $10^{18}$ eV to a level of $E^{2}Φ_{ν_{e}+ν_{μ}+ν_{τ}}≃10^{-8}$ GeV cm$^{-2}$ s$^{-1} sr$^{-1}$, the most stringent limit to date. Using these data, we constrain the proton fraction of ultrahigh-energy cosmic rays (UHECRs) above ≃30 EeV to be ≲70% (at 90% CL) if the cosmological evolution of the sources is comparable to or stronger than the star formation rate. This is the first result to disfavor the "proton-only" hypothesis for UHECR in this evolution regime using neutrino data. This result complements direct air-shower measurements by being insensitive to uncertainties associated with hadronic interaction models. We also evaluate the tension between IceCube's nonobservation and the ∼200 PeV KM3NeT neutrino candidate (KM3-230213A), finding it to be ∼2.9σ based on a joint-livetime fit between neutrino datasets.
Abbasi, R. [Loyola University Chicago] (ORCID:0000↗
Description of Differential Cross Sections for {sup 63}Cu + p Nuclear Reactions Induced by High-Energy Cosmic-Ray Protons
The results of calculation of {sup 63}Cu + p differential cross sections at incident-proton energies between 10 and 200 MeV and a comparative analysis of these results are presented as a continuation of the earlier work of our group on developing methods for calculating the contribution of nuclear reactions to radiative effects arising in the onboard spacecraft electronics under the action of high-energy cosmic-ray protons on {sup 63}Cu nuclei (generation of single-event upsets) and as a supplement to the earlier calculations performed on the basis of the TАLYS code in order to determine elastic- and inelastic-scattering cross sections and charge, mass, and energy distributions of recoil nuclei (heavy products of the {sup 63}Cu + p nuclear reaction). The influence of various mechanisms of the angular distributions of particles emitted in the {sup 63}Cu + p nuclear reaction is also discussed.
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SENSITIVITY OF COSMIC-RAY PROTON SPECTRA TO THE LOW-WAVENUMBER BEHAVIOR OF THE 2D TURBULENCE POWER SPECTRUM
In this study, a novel ab initio cosmic ray (CR) modulation code that solves a set of stochastic transport equations equivalent to the Parker transport equation, and that uses output from a turbulence transport code as input for the diffusion tensor, is introduced. This code is benchmarked with a previous approach to ab initio modulation. The sensitivity of computed galactic CR proton spectra at Earth to assumptions made as to the low-wavenumber behavior of the two-dimensional (2D) turbulence power spectrum is investigated using perpendicular mean free path expressions derived from two different scattering theories. Constraints on the low-wavenumber behavior of the 2D power spectrum are inferred from the qualitative comparison of computed CR spectra with spacecraft observations at Earth. Another key difference from previous studies is that observed and inferred CR intensity spectra at 73 AU are used as boundary spectra instead of the usual local interstellar spectrum. Furthermore, the results presented here provide a tentative explanation as to the reason behind the unusually high galactic proton intensity spectra observed in 2009 during the recent unusual solar minimum.
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NEW CALCULATION OF ANTIPROTON PRODUCTION BY COSMIC RAY PROTONS AND NUCLEI
A dramatic increase in the accuracy and statistics of space-borne cosmic ray (CR) measurements has yielded several breakthroughs over the last several years. The most puzzling is the rise in the positron fraction above ∼10 GeV over the predictions of the propagation models assuming pure secondary production. The accuracy of the antiproton production cross section is critical for astrophysical applications and searches for new physics since antiprotons in CRs seem to hold the keys to many puzzles including the origin of those excess positrons. However, model calculations of antiproton production in CR interactions with interstellar gas are often employing parameterizations that are out of date or are using outdated physical concepts. This may lead to an incorrect interpretation of antiproton data which could have broad consequences for other areas of astrophysics. In this work, we calculate antiproton production in pp-, pA-, and AA-interactions using EPOS-LHC and QGSJET-II-04, two of the most advanced Monte Carlo (MC) generators tuned to numerous accelerator data including those from the Large Hadron Collider (LHC). We show that the antiproton yields obtained with these MC generators differ by up to an order of magnitude from yields of parameterizations commonly used in astrophysics.
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IceCube constraints on fast-spinning pulsars as high-energy neutrino sources
Relativistic winds of fast-spinning pulsars have been proposed as a potential site for cosmic-ray acceleration from very high energies (VHE) to ultrahigh energies (UHE). We re-examine conditions for high-energy neutrino production, considering the interaction of accelerated particles with baryons of the expanding supernova ejecta and the radiation fields in the wind nebula. We make use of the current IceCube sensitivity in diffusive high-energy neutrino background, in order to constrain the parameter space of the most extreme neutron stars as sources of VHE and UHE cosmic rays. We demonstrate that the current non-observation of 10{sup 18} eV neutrinos put stringent constraints on the pulsar scenario. For a given model, birthrates, ejecta mass and acceleration efficiency of the magnetar sources can be constrained. When we assume a proton cosmic ray composition and spherical supernovae ejecta, we find that the IceCube limits almost exclude their significant contribution to the observed UHE cosmic-ray flux. Furthermore, we consider scenarios where a fraction of cosmic rays can escape from jet-like structures piercing the ejecta, without significant interactions. Such scenarios would enable the production of UHE cosmic rays and help remove the tension between their EeV neutrino production and the observational data.
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Transport of cosmic-ray protons in intermittent heliospheric turbulence: Model and simulations
The transport of charged energetic particles in the presence of strong intermittent heliospheric turbulence is computationally analyzed based on known properties of the interplanetary magnetic field and solar wind plasma at 1 astronomical unit. The turbulence is assumed to be static, composite, and quasi-three-dimensional with a varying energy distribution between a one-dimensional Alfvénic (slab) and a structured two-dimensional component. The spatial fluctuations of the turbulent magnetic field are modeled either as homogeneous with a Gaussian probability distribution function (PDF), or as intermittent on large and small scales with a q-Gaussian PDF. Simulations showed that energetic particle diffusion coefficients both parallel and perpendicular to the background magnetic field are significantly affected by intermittency in the turbulence. This effect is especially strong for parallel transport where for large-scale intermittency results show an extended phase of subdiffusive parallel transport during which cross-field transport diffusion dominates. The effects of intermittency are found to depend on particle rigidity and the fraction of slab energy in the turbulence, yielding a perpendicular to parallel mean free path ratio close to 1 for large-scale intermittency. Investigation of higher order transport moments (kurtosis) indicates that non-Gaussian statistical properties of the intermittent turbulent magnetic field are present in the parallel transport, especially for low rigidity particles at all times.
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Evolution and feedback of AGN jets of different cosmic ray composition
Jet feedback from active galactic nuclei (AGN) is one of the most promising mechanisms for suppressing cooling flows in cool-core clusters. However, the composition of AGN jets and bubbles remains uncertain; they could be thermally dominated, or dominated by cosmic ray proton (CRp), cosmic ray electron (CRe), or magnetic energy. In this work, we investigate the evolution and feedback effects of CRp and CRe dominated jets by conducting 3D magnetohydrodynamic simulations of AGN jet-inflated bubbles in the intracluster medium using the FLASH code. We present the evolution of their energies, dynamics, and heating, and model their expected cavity-power versus radio-luminosity relation (P cav –L R ). We find that bubbles inflated by CRe dominated jets follow a very similar dynamical evolution to CRp dominated bubbles even though CRe within bubbles suffer significantly stronger synchrotron and inverse-Compton cooling. This is because, as CRe lose their energy, the jet-inflated bubbles quickly become thermally dominated within ∼30 Myr. Their total energy stops decreasing with CR energy and evolves similarly to CRp dominated bubbles. The ability of CRe and CRp dominated bubbles to heat the intracluster medium is also comparable; the cold gas formed via local thermal instabilities is well suppressed in both cases. The CRp and CRe bubbles follow different evolutionary trajectories on the P cav –L R plane, but the values are broadly consistent with observed ranges for FR-I sources. We also discuss observational techniques that have potential for constraining the composition of AGN jets and bubbles.
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DISCOVERY OF THE HARD SPECTRUM VHE γ-RAY SOURCE HESS J1641–463
This Letter reports the discovery of a remarkably hard spectrum source, HESS J1641–463, by the High Energy Stereoscopic System (H.E.S.S.) in the very high energy (VHE) domain. HESS J1641–463 remained unnoticed by the usual analysis techniques due to confusion with the bright nearby source HESS J1640–465. It emerged at a significance level of 8.5 standard deviations after restricting the analysis to events with energies above 4 TeV. It shows a moderate flux level of φ(E>1 TeV) = (3.64 ± 0.44{sub stat} ± 0.73{sub sys}) × 10{sup –13} cm{sup –2} s{sup –1}, corresponding to 1.8% of the Crab Nebula flux above the same energy, and a hard spectrum with a photon index of Γ = 2.07 ± 0.11{sub stat} ± 0.20{sub sys}. It is a point-like source, although an extension up to a Gaussian width of σ = 3 arcmin cannot be discounted due to uncertainties in the H.E.S.S. point-spread function. The VHE γ-ray flux of HESS J1641–463 is found to be constant over the observed period when checking time binnings from the year-by-year to the 28 minute exposure timescales. HESS J1641–463 is positionally coincident with the radio supernova remnant SNR G338.5+0.1. No X-ray candidate stands out as a clear association; however, Chandra and XMM-Newton data reveal some potential weak counterparts. Various VHE γ-ray production scenarios are discussed. If the emission from HESS J1641–463 is produced by cosmic ray protons colliding with the ambient gas, then their spectrum must extend close to 1 PeV. This object may represent a source population contributing significantly to the galactic cosmic ray flux around the knee.
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PROSPECTS FOR DETECTION OF SYNCHROTRON EMISSION FROM SECONDARY ELECTRONS AND POSITRONS IN STARLESS CORES: APPLICATION TO G0.216+0.016
We investigate the diffusion of cosmic rays into molecular cloud complexes. Using the cosmic-ray diffusion formalism of Protheroe et al., we examine how cosmic rays diffuse into clouds exhibiting different density structures, including a smoothed step-function, as well as Gaussian and inverse-r density distributions, which are well known to trace the structure of star-forming regions. These density distributions were modeled as an approximation to the Galactic center cloud G0.216+0.016, a recently discovered massive dust clump that exhibits limited signs of massive star formation and thus may be the best region in the Galaxy to observe synchrotron emission from secondary electrons and positrons. Examination of the resulting synchrotron emission, produced by the interaction of cosmic-ray protons interacting with ambient molecular matter producing secondary electrons and positrons reveals that, due to projection effects, limb-brightened morphology results in all cases. However, we find that the Gaussian and inverse-r density distributions show much broader flux density distributions than step-function distributions. Significantly, some of the compact (compared to the 2.''2 resolution, 5.3 GHz Karl G. Jansky Very Large Array (JVLA) observations) sources show non-thermal emission, which may potentially be explained by the density structure and the lack of diffusion of cosmic rays into the cloud. We find that we can match the 5.3 and 20 GHz flux densities of the non-thermal source JVLA 1 and 6 from Rodríguez and Zapata with a local cosmic-ray flux density, a diffusion coefficient suppression factor of χ = 0.1-0.01 for a coefficient of 3 × 10{sup 27} cm{sup –2} s{sup –1}, and a magnetic field strength of 470 μG.
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