Abstract The very high energy (VHE) emission of the central molecular zone (CMZ) is rarely modeled 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 γ -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 favored. Future missions such as the upcoming CTA will reveal more small-scale structures that are not yet included in the model. Therefore, a more detailed 3D gas distribution and magnetic field structure will be needed.
Abstract
Astro-COLIBRI is a novel tool that evaluates alerts of transient observations in real time, filters them by user-specified criteria, and puts them into their multiwavelength and ...multimessenger context. Through fast generation of an overview of persistent sources as well as transient events in the relevant phase space, Astro-COLIBRI contributes to an enhanced discovery potential of both serendipitous and follow-up observations of the transient sky. The software’s architecture comprises a Representational State Transfer Application Programming Interface, both a static and a real-time database, a cloud-based alert system, as well as a website and apps for iOS and Android as clients for users. The latter provide a graphical representation with a summary of the relevant data to allow for the fast identification of interesting phenomena along with an assessment of observing conditions at a large selection of observatories around the world.
Context. The observation of charged cosmic rays with energies up to 1020 eV shows that particle acceleration must occur in astrophysical sources. Acceleration of secondary particles like muons and ...pions, produced in cosmic ray interactions, are usually neglected, however, when calculating the flux of neutrinos from cosmic ray interactions. Aims. Here, we discuss the acceleration of secondary muons, pions, and kaons in gamma-ray bursts (GRBs) within the internal shock scenario, and their impact on the neutrino fluxes. Methods. We introduce a two-zone model consisting of an acceleration zone (the shocks) and a radiation zone (the plasma downstream the shocks). The acceleration in the shocks, which is an unavoidable consequence of efficient proton acceleration, requires efficient transport from the radiation back to the acceleration zone. On the other hand, stochastic acceleration in the radiation zone can enhance the secondary spectra of muons and kaons significantly if there is a sufficiently large turbulent region. Results. Overall, it is plausible that neutrino spectra can be enhanced by up to a factor of two at the peak by stochastic acceleration, that an additional spectral peak appears from shock acceleration of the secondary muons and pions, and that the neutrino production from kaon decays is enhanced. Conclusions. Depending on the GRB parameters, the general conclusions concerning the limits to the internal shock scenario obtained by recent IceCube and ANTARES analyses may be affected by up to a factor of two by secondary acceleration. Most of the changes occur at energies above 107 GeV, so the effects for next-generation radio-detection experiments will be more pronounced. In the future, however, if GRBs are detected as high-energy neutrino sources, the detection of one or several pronounced peaks around 106 GeV or higher energies could help to derive the basic properties of the magnetic field strength in the GRB.
The search for astrophysical high-energy neutrinos is one of the most important approaches to pin-point the sources of cosmic rays. The advantage of using these neutral and only weakly-interacting ...particles as messengers in order to look deep into the sources themselves is at the same time the main challenge, as extremely large detectors are needed to measure a significant signal. With the finalization of the large underground detectors IceCube and ANTARES, the quantity and the quality of the recorded data are now at a stage where many analyses have a sensitivity limited by the systematic error rather than statistical uncertainties. Such an error source is the Monte Carlo description of the lepton energy losses before a lepton reaches the detector and of all leptons within the detector. A very accurate simulation of the propagation of muons through large amount of matter is needed because a muon may sustain hundreds of interactions before it is detected by the experiment. Requirements on the precision of the muon propagation code are very stringent. A stochastical correct description of the series of lepton interactions within the detector is needed for a correct conclusion from the measured signature to the lepton energy respectively neutrino energy. In this paper, the Monte Carlo code PROPOSAL (Propagator with optimal precision and optimized speed for all leptons) is presented as a public tool for muon propagation through transparent media. Up-to-date cross sections for ionization, bremsstrahlung, photonuclear interactions, electron pair production, Landau–Pomeranchuk–Migdal and Ter-Mikaelian effects, muon and tau decay, as well as Molière scattering are implemented for different parametrizations. Thus, a full study of the systematic uncertainties is possible from the theoretical description of lepton energy loss in the context of high-energy neutrino analyses and other astroparticle physics experiments that rely on the proper description of lepton propagation. A numerical precision of better than 10−6 is achieved, setting the systematic error for high-energy neutrino analyses to a minimum from the numerical prospective.
The cosmic-ray Sun shadow, which is caused by high-energy charged cosmic rays being blocked and deflected by the Sun and its magnetic field, has been observed by various experiments, such as ...Argo-YBJ, Tibet, HAWC, and IceCube. Most notably, the shadow’s size and depth was recently shown to correlate with the 11-year solar cycle. The interpretation of such measurements, which help to bridge the gap between solar physics and high-energy particle astrophysics, requires a solid theoretical understanding of cosmic-ray propagation in the coronal magnetic field. It is the aim of this paper to establish theoretical predictions for the cosmic-ray Sun shadow in order to identify observables that can be used to study this link in more detail. To determine the cosmic-ray Sun shadow, we numerically compute trajectories of charged cosmic rays in the energy range of 5−316 TeV for five different mass numbers. We present and analyze the resulting shadow images for protons and iron, as well as for typically measured cosmic-ray compositions. We confirm the observationally established correlation between the magnitude of the shadowing effect and both the mean sunspot number and the polarity of the magnetic field during the solar cycle. We also show that during low solar activity, the Sun’s shadow behaves similarly to that of a dipole, for which we find a non-monotonous dependence on energy. In particular, the shadow can become significantly more pronounced than the geometrical disk expected for a totally unmagnetized Sun. For times of high solar activity, we instead predict the shadow to depend monotonously on energy and to be generally weaker than the geometrical shadow for all tested energies. These effects should become visible in energy-resolved measurements of the Sun shadow, and may in the future become an independent measure for the level of disorder in the solar magnetic field.
CRPropa - A Toolbox for Cosmic Ray Simulations Alves Batista, R.; Becker Tjus, J.; Dundovic, A. ...
Journal of physics. Conference series,
02/2019, Letnik:
1181, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The astrophysical interpretation of recent experimental observations of cosmic rays relies increasingly on Monte Carlo simulations of cosmic ray propagation and acceleration. Depending on the energy ...range of interest, several different propagation effects inside the Milky Way as well as in extragalactic space have to be taken into account when interpreting the data. With the CRPropa framework we aim to provide a toolbox for according simulations. In recent versions of CRPropa, the ballistic single particle propagation mode aiming primarily at extragalactic cosmic rays has been complemented by a solver for the differential transport equation to address propagation of galactic cosmic rays. Additionally, modules have been developed to address cosmic ray acceleration and many improvements have been added for simulations of electromagnetic secondaries. In this contribution we will give an overview of the CRPropa simulation framework with a focus on the latest improvements and highlight selected features by example applications.
Moon shadow analyses are standard methods to calibrate cosmic-ray detectors. We report on a three-year observation of cosmic-ray Moon and Sun shadows in different detector configurations. The ...cosmic-ray Moon shadow was observed with high statistical significance (> 6σ) in previous analyses when the IceCube detector operated in a smaller configuration before it was completed in December 2010. This work shows first analyses of the cosmic-ray Sun shadow in IceCube. A binned analysis in one-dimension is used to measure the Moon and Sun shadow with high statistical significance greater than 12σ.
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.
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