The extended jet structures of radio galaxies (RGs) represent an ideal acceleration site for High Energy Cosmic Rays (HECRs) and a recent model showed that the HECR data can be explained by these ...sources, if the arrival directions of HECRs at energies ≲8EeV from a certain RG, Cygnus A, are isotropized. First, this work introduces the inverted simulation setup in order to probe the isotropy assumption. Here, different extragalactic magnetic field models are compared showing that either a magnetic field of primordial origin that yields a high field strength in the large scale structures of the Universe is needed, or a significant contribution by a multitude of isotropically distributed sources. Secondly, the HECRs contribution by the bulk of RGs of different Fanaroff-Riley (FR) type is determined. Here, the most recent FR-type dependent radio-to-CR correlations Qcr∝LradioβL} are used, and the impact of the slope βL on the HECRs is analyzed in detail. Finally, it is carved out that FR-II RGs provide a promising spectral behavior at the hardening part of the CR flux, between about 3EeV and 30EeV, but most likely not enough CR power. At these energies, FR-I RGs can only provide an appropriate flux in the case of a high acceleration efficiency and βL≳0.9, otherwise these sources rather contribute below 3EeV. Further, the required acceleration efficiency for a significant HECR contribution is exposed dependent on βL and the CR spectrum at the acceleration site.
ABSTRACT We present a systematic study of non-thermal electron-proton plasma and its emission processes in starburst galaxies in order to explain the correlation between the luminosity in the radio ...band and the recently observed gamma luminosity. In doing so, a steady state description of the cosmic-ray (CR) electrons and protons within the spatially homogeneous starburst is considered where continuous momentum losses are included as well as catastrophic losses due to diffusion and advection. The primary source of the relativistic CRs, e.g., supernova remnants, provides a quasi-neutral plasma with a power-law spectrum in momentum where we account for rigidity-dependent differences between the electron and proton spectrum. We examine the resulting leptonic and hadronic radiation processes by synchrotron radiation, inverse Compton scattering, Bremsstrahlung, and hadronic pion production. Finally, the observations of NGC 253, M82, NGC 4945, and NGC 1068 in the radio and gamma-ray bands as well as the observed supernova rate are used to constrain a best-fit model. In the case of NGC 253, M82, and NGC 4945 our model is able to accurately describe the data, showing that: (i) supernovae are the dominant particle accelerators for NGC 253, M82, and NGC 4945, but not for NGC 1068; (ii) all considered starburst galaxies are poor proton calorimeters in which for NGC 253 the escape is predominantly driven by the galactic wind, whereas the diffusive escape dominates in NGC 4945 and M82 (at energies >1 TeV); and (iii) secondary electrons from hadronic pion production are important to model the radio flux, but the associated neutrino flux is below the current observation limit.
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.
Abstract
Radio galaxies are promising candidates as the sources of ultrahigh energy
cosmic rays (UHECRs). In this work, we examine if the stringent constraints
imposed by the dipole and quadropole ...anisotropies as well as the UHECR
spectrum and composition allow that radio galaxies are the dominant
extragalactic cosmic ray sources. In order to calculate the UHECR flux
emitted by individual
radio galaxies, we constrain their properties using information from the
radio-CR correlation and a dynamical evolution model. In
addition to the UHECR flux from individual, local sources, we
include the diffuse flux emitted by the bulk of non-local radio galaxies based
on their radio luminosity distribution. Analyzing the source parameters within
a range around their expected properties, we finally determine the
configurations of local sources describing well the UHECR spectrum, composition
and large-scale anisotropies. We obtain a good description of all data
even in the case that we include only a small number of local sources. In
particular, we find that scenarios where few sources like Fornax A and Virgo A
dominate the flux above the ankle, while low-luminosity radio galaxies
contribute an isotropic background dominating below the ankle,
provide a good fit to the data.
Abstract
The observational data on ultrahigh energy cosmic rays (UHECR), in particular their mass
composition, show strong indications for extremely hard spectra of individual mass groups of CR
...nuclei at Earth. In this work, we show that such hard spectra can be the result of the finite
life-time of UHECR sources, if a few individual sources dominate the UHECR flux at the highest
energies. In this case, time delays induced by deflections in the turbulent extragalactic
magnetic field as well as from the diffusive or advective escape from the source environment can
suppress low-energy CRs, leading to a steepening of the observed spectrum. Considering radio
galaxies as the main source of UHECRs, we discuss the necessary conditions that few individual
sources dominate over the total contribution from the bulk of sources that have been active in the
past. We provide two proof-of-principle scenarios showing that for a turbulent extragalactic
magnetic field with a strength
B
and a coherence length
l
coh
, the life-time of a source
at a distance
d
src
should satisfy
t
act
∼ (
B
/1 nG)
2
(
d
src
/10 Mpc)
2
(
l
coh
/1 Mpc) Myr to obtain the necessary hardening of the CR spectrum at Earth.
Numerical simulations of the propagation of charged particles through magnetic fields solving the equation of motion often leads to the usage of an interpolation in the case of discretely defined ...magnetic fields, typically given on a homogeneous grid structure. However, the interpolation method influences the magnetic field properties and, therefore, also the propagation of particles through these fields. To determine the resulting error, we compare three different interpolation routines-trilinear, tricubic, and nearest neighbor interpolation-in the case of isotropic, turbulent magnetic fields. First, we analyze the impact of the different interpolation methods on the root mean square field strength, the divergence, and the spectrum of the turbulent magnetic field. Here, the nearest neighbor interpolation shows some clear benefits compared with the trilinear method; however, that changes significantly if we consider the particle propagation. In principle, a better interpolation method also yields a better description of the particle transport. In the case of field line random walk, it is shown that none of these methods, especially not the nearest neighbor interpolation, is able to yield an accurate description of the diffusion coefficient, exposing the need for a continuous, grid-less turbulent magnetic field. We optimize the performance of an algorithm that generates such a magnetic field by more than an order of magnitude. Further, the necessary number of wave-modes is determined, so that this continuous method supports realistic simulations over a larger energy range without limitations by the available memory.
NGC 1068 is a nearby, widely studied Seyfert II galaxy presenting radio, infrared, X-ray, and γ -ray emission, along with strong evidence for high-energy neutrino emission. Recently, the evidence for ...neutrino emission was explained in a multimessenger model, whereby the neutrinos originate from the corona of the active galactic nucleus. In this environment, γ -rays are strongly absorbed, so that an additional contribution is necessary, for instance, from the circumnuclear starburst ring. In this work, we discuss whether the radio jet can be an alternative source of the γ -rays between about 0.1 and 100 GeV, as observed by Fermi -LAT. In particular, we include both leptonic and hadronic processes, namely, accounting for inverse Compton emission and signatures from pp as well as pγ interactions. In order to constrain our calculations, we used VLBA and ALMA observations of the radio knot structures, which are spatially resolved at different distances from the supermassive black hole. Our results show that the best leptonic scenario for the prediction of the Fermi -LAT data is provided by the radio knot closest to the central engine. For that to be the case, a magnetic field strength of ∼1 mG is needed as well as a strong spectral softening of the relativistic electron distribution at (1 − 10) GeV. However, we show that neither such a weak magnetic field strength, nor such a strong softening is expected for that knot. A possible explanation for the ∼10 GeV γ -rays could potentially be provided by hadronic pion production in case of a gas density ≳10 4 cm −3 . Nonetheless, this process is not found to contribute significantly to the low-energy end of the Fermi -LAT range. We conclude that the emission sites in the jet are not sufficient to explain the γ -rays across the whole Fermi -LAT energy band.
Most studies of resistance training (RT) examine methods that do not resemble typical training practices of persons participating in RT. Ecologically valid RT programs more representative of such ...practices are seldom compared. This study compared two such approaches to RT. Thirty participants (males, n = 13; females, n = 17) were randomised to either a group performing low volume 'High Intensity Training' (HIT; n = 16) or high volume 'Body-building' (3ST; n = 14) RT methods 2x/week for 10 weeks. Outcomes included muscular performance, body composition, and participant's subjective assessments. Both HIT and 3ST groups improved muscular performance significantly (as indicated by 95% confidence intervals) with large effect sizes (ES; 0.97 to 1.73 and 0.88 to 1.77 respectively). HIT had significantly greater muscular performance gains for 3 of 9 tested exercises compared with 3ST (p < 0.05) and larger effect sizes for 8 of 9 exercises. Body composition did not significantly change in either group. However, effect sizes for whole body muscle mass changes were slightly more favourable in the HIT group compared with the 3ST group (0.27 and -0.34 respectively) in addition to whole body fat mass (0.03 and 0.43 respectively) and whole body fat percentage (-0.10 and -0.44 respectively). Significant muscular performance gains can be produced using either HIT or 3ST. However, muscular performance gains may be greater when using HIT. Future research should look to identify which components of ecologically valid RT programs are primarily responsible for these differences in outcome.
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