Massive stars play an important role in explaining the cosmic ray spectrum below the knee, possibly even up to the ankle, i.e. up to energies of 1015 or 1018.5 eV, respectively. In particular, ...Supernova Remnants are discussed as one of the main candidates to explain the cosmic ray spectrum. Even before their violent deaths, during the stars' regular life times, cosmic rays can be accelerated in wind environments. High-energy gamma-ray measurements indicate hadronic acceleration binary systems, leading to both periodic gamma-ray emission from binaries like LSI + 60 303 and continuous emission from colliding wind environments like η-Carinae. The detection of neutrinos and photons from hadronic interactions are one of the most promising methods to identify particle acceleration sites. In this paper, future prospects to detect neutrinos from colliding wind environments in massive stars are investigated. In particular, the seven most promising candidates for emission from colliding wind binaries are investigated to provide an estimate of the signal strength. The expected signal of a single source is about a factor of 5–10 below the current IceCube sensitivity and it is therefore not accessible at the moment. What is discussed in addition is future the possibility to measure low-energy neutrino sources with detectors like PINGU and ORCA: the minimum of the atmospheric neutrino flux at around 25 GeV from neutrino oscillations provides an opportunity to reduce the background and increase the significance to searches for GeV–TeV neutrino sources. This paper presents the first idea, detailed studies including the detector's effective areas will be necessary in the future to test the feasibility of such an approach.
It is generally believed that the cosmic ray spectrum below the knee is of Galactic origin, although the exact sources making up the entire cosmic ray energy budget are still unknown. Including ...effects of magnetic amplification, Supernova Remnants (SNR) could be capable of accelerating cosmic rays up to a few PeV and they represent the only source class with a sufficient non-thermal energy budget to explain the cosmic ray spectrum up to the knee. Now, gamma-ray measurements of SNRs for the first time allow to derive the cosmic ray spectrum at the source, giving us a first idea of the concrete, possible individual contributions to the total cosmic ray spectrum. In this contribution, we use these features as input parameters for propagating cosmic rays from its origin to Earth using GALPROP in order to investigate if these supernova remnants reproduce the cosmic ray spectrum and if supernova remnants in general can be responsible for the observed energy budget.
ABSTRACT Understanding the transport of energetic cosmic rays belongs to the most challenging topics in astrophysics. Diffusion due to scattering by electromagnetic fluctuations is a key process in ...cosmic ray transport. The transition from a ballistic to a diffusive-propagation regime is presented in direct numerical calculations of diffusion coefficients for homogeneous magnetic field lines subject to turbulent perturbations. Simulation results are compared with theoretical derivations of the parallel diffusion coefficient’s dependences on the energy and the fluctuation amplitudes in the limit of weak turbulence. The present study shows that the widely used extrapolation of the energy scaling for the parallel diffusion coefficient to high turbulence levels predicted by quasi-linear theory does not provide a universally accurate description in the resonant-scattering regime. It is highlighted here that the numerically calculated diffusion coefficients can be polluted for low energies due to missing resonant interaction possibilities of the particles with the turbulence. Five reduced-rigidity regimes are established, which are separated by analytical boundaries derived in this work. Consequently, a proper description of cosmic ray propagation can only be achieved by using a turbulence-level-dependent diffusion coefficient and can contribute to solving the Galactic cosmic ray gradient problem.
High-energy neutrinos from radio galaxies Becker Tjus, J.; Eichmann, B.; Halzen, F. ...
Physical review. D, Particles, fields, gravitation, and cosmology,
06/2014, Letnik:
89, Številka:
12
Journal Article
The IceCube experiment has recently reported the first observation of high-energy cosmic neutrinos. Their origin is still unknown. In this paper, we investigate the possibility that they originate in ...active galaxies. We show that hadronic interactions (pp) in the generally less powerful, more frequent, FR-I radio galaxies are one of the candidate source classes being able to accommodate the observation while the more powerful, less frequent, class of FR-II radio galaxies has too low of a column depths to explain the signal.
The statistics of black holes and their masses strongly suggests that their mass distribution has a cut-off towards lower masses near 3 × 106 M⊙. This is consistent with a classical formation ...mechanism from the agglomeration of the first massive stars in the universe. However, when the masses of the stars approach 106 M⊙, the stars become unstable and collapse, possibly forming the first generation of cosmological black holes. Here, we speculate that the claimed detection of an isotropic radio background may constitute evidence of the formation of these first supermassive black holes, since their data are compatible in spectrum and intensity with synchrotron emission from the remnants. The model proposed fulfils all observational conditions for the background, in terms of single-source strength, number of sources, far-infrared and gamma-ray emission. The observed high-energy neutrino flux is consistent with our calculations in flux and spectrum. The proposal described in this paper may also explain the early formation and growth of massive bulge-less disc galaxies as derived from the massive, gaseous shell formed during the explosion prior to the formation of a supermassive black hole.
In astrophysics, the search for sources of the highest-energy cosmic rays continues. For further progress, not only ever better observatories but also ever more realistic numerical simulations are ...needed. We compare different approaches for numerical test simulations of UHECRs in the IGMF and show that all methods provide correct statistical propagation characteristics of the particles in means of their diffusive behaviour. Through convergence tests, we show that the necessary requirements for the methods differ and ultimately reveal significant differences in the required simulation time.
NGC 1068 is a nearby widely studied Seyfert II galaxy presenting radio, infrared, X- and \(\gamma\)-ray emission as well as strong evidence for high-energy neutrino emission. Recently, the evidence ...for neutrino emission could be explained in a multimessenger model in which the neutrinos originate from the corona of the active galactic nucleus (AGN). In this environment \(\gamma\)-rays are strongly absorbed, so that an additional contribution from e.g. the circumnuclear starburst ring is necessary. In this work, we discuss whether the radio jet can be an alternative source of the \(\gamma\)-rays between about \(0.1\) and \(100\) GeV as observed by Fermi-LAT. In particular, we include both leptonic and hadronic processes, i.e. accounting for inverse Compton emission and signatures from \(pp\) as well as \(p\gamma\) interactions. In order to constrain our calculations, we use 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 a magnetic field strength \(\sim 1\,\text{mG}\) is needed as well as a strong spectral softening of the relativistic electron distribution at \((1-10)\,\text{GeV}\). 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 \(\sim\) 10 GeV \(\gamma\)-rays can be provided by hadronic pion production in case of a gas density \(\gtrsim 10^4\,\text{cm}^{-3}\). Nonetheless, this process cannot contribute significantly to the low energy end of the Fermi-LAT range. We conclude that the emission sites in the jet are not able to explain the \(\gamma\)-rays in the whole Fermi-LAT energy band.
The very high energy (VHE) emission of the Central Molecular Zone (CMZ) is rarely modelled in 3D. Most approaches describe the morphology in 1D or simplify the diffusion to the isotropic case. In ...this work we show the impact of a realistic 3D magnetic field configuration and gas distribution on the VHE gamma-ray distribution of the CMZ. We solve the 3D cosmic-ray transport equation with an anisotropic diffusion tensor using the approach of stochastic differential equations as implemented in the CRPropa framework. We test two different source distributions for five different anisotropies of the diffusion tensor, covering the range of effectively fieldline-parallel diffusion to isotropic diffusion. Within the tested magnetic field configuration the anisotropy of the diffusion tensor is close to the isotropic case and three point sources within the CMZ are favoured. Future missions like the upcoming CTA will reveal more small-scale structures which are not jet included in the model. Therefor a more detailed 3D gas distribution and magnetic field structure will be needed.
The study of flaring astrophysical events in the multi-messenger approach requires instantaneous follow-up observations to better understand the nature of these events through complementary ...observational data. We present Astro-COLIBRI as a platform that integrates specific tools in the real-time multi-messenger ecosystem. The Astro-COLIBRI platform bundles and evaluates alerts about transients from various channels. It further automates the coordination of follow-up observations by providing and linking detailed information through its comprehensible graphical user interface. We present the functionalities with documented examples of Astro-COLIBRI usage through the community since its public release in August 2021. We highlight the use cases of Astro-COLIBRI for planning follow-up observations by professional and amateur astronomers, as well as checking predictions from theoretical models.
On September 18, 2022, an alert by ceCube indicated that a ~170TeV neutrino arrived in directional coincidence with the blazar TXS 0506+056. This event adds to two previous ones: a neutrino alert ...from its direction on September 22, 2017, and a 3sigma signature of a dozen neutrinos in 2014/2015. deBruijn 2020 showed that these two previous neutrino emission episodes could be due to a supermassive binary black hole (SMBBH) where jet precession close to final coalescence results in periodic emission. This model predicted a new emission episode consistent with the September 18, 2022 neutrino observation. Here, we show that the neutrino cadence of TXS 0506+056 is consistent with a SMBBH origin with mass ratios q<0.3 for a total black hole mass of M>3e8Msun. For the first time, we calculate the characteristic strain of the gravitational wave emission of the binary, and show that the merger could be detectable by LISA for black hole masses <5e8Msun if the mass ratios are in the range 0.1<q<0.3. We predict that there can be a neutrino flare existing in the still to be analyzed IceCube data peaking some time between 08/2019 and 01/2021 if a precessing jet is responsible for all three detected emission episodes. The next flare is expected to peak in the period 01/2023 to 08/2026. Further observation will make it possible to constrain the mass ratio as a function of the black hole mass more precisely and would open the window toward the preparation of the detection of SMBBH mergers.
PDF
