117 research outputs found
Propagation of ultrahigh energy cosmic rays in extragalactic magnetic fields: a view from cosmological simulations
No full textWe use the crpropa code to simulate the propagation of ultrahigh energy cosmic rays (with energy â¥1018eV and pure proton composition) through extragalactic magnetic fields that have been simulated with the cosmological enzo code. We test both primordial and astrophysical magnetogenesis scenarios in order to investigate the impact of different magnetic field strengths in clusters, filaments and voids on the deflection of cosmic rays propagating across cosmological distances. We also study the effect of different source distributions of cosmic rays around simulated Milky Way-like observers. Our analysis shows that the arrival spectra and anisotropy of events are rather insensitive to the distribution of extragalactic magnetic fields, while they are more affected by the clustering of sources within an ~50 Mpc distance to observers. Finally, we find that in order to reproduce the observed degree of isotropy of cosmic rays at ~EeV energies, the average magnetic fields in cosmic voids must be ~ 0.1 nG, providing limits on the strength of primordial seed fields
Über Anisotropien der ultrahochenergetischen kosmischen Strahlung
No full textDiese Dissertation behandelt den Einfluß der Verteilung der Quellen kosmischer Strahlung sowie der kosmischen Magnetfelder auf die Anisotropie von Einfallsrichtungen kosmischer Strahlung mit Fokus auf ultra-hohe Energien. Präsentiert werden die zwei hauptsächlichen Untersuchungen dieses Sachverhalts sowie eine Nebenthematik, welche für diese beiden wichtig ist.
Der erste Themenbereich befasst sich mit der Anisotropie verursacht durch eine einzige Quelle, wobei der Beitrag aller anderen Quellen als isotrop angenommen wird. Der Fluss kosmischer Strahlung wird beeinflusst von turbulenten Magnetfeldern, welche die Einfallsrichtungen zerstreuen. Diese Zerstreuung wird mit einer Fisher Distribution nachgestellt. Dieses Modell wird dann eingeschränkt durch Vergleich mit Messungen des Pierre Auger Observatoriums, insbesondere der beobachteten dipolaren Anisotropie. Mit der Kleinwinkelnäherung ergibt sich der quadratische Mittelwert des Ablenkungswinkels zur Sichtlinie zu 50 +11/-10 Grad. Es wird gezeigt, dass der Ablenkungswinkel noch größ er wäre, falls die Teilchen verschiedene Gebiete eines strukturierten Feldes passieren würden. Die Anwendung dessen auf zwei potenzielle Quellen, Cen A und das Virga Cluster, liefert eine Abschätzung der Kohärenzlänge und Feldstärke des dazwischenliegenden tubulenten Magnetfeldes.
Der zweite Themenbereich behandelt die Auswirkung von Magnetfeldern auf Anisotropien indem es die Anwendbarkeit von Liouville's Theorem auf kosmische Strahlung untersucht. Das Konzept des Einfangens kosmischer Strahlung wurde herausgestellt als eine potenzielle Ursache von Anisotropien und ein Beispiel dessen Anwendung wird demonstriert. Das Einfangen in einem strukturierten feld kann dipolare Anisotropien hervorrufen.
Das Nebenthema erforscht den Übergang von geradliniger zu diffusiver Propagation und leitet ein präzises Kriterium für den Fall turbulenter Magnetfelder ab.This dissertation deals with the influence of cosmic ray source distributions and cosmic magnetic fields on anisotropies in the arrival directions with a focus on the ultra-high energy range. Two main investigations regarding the subject are presented and one side topic important for the first two.
The first topic is the study of anisotropies caused by a single source where the rest of sources are contributing only isotropically. The cosmic ray flux is affected by a turbulent magnetic field which spreads the arrival directions, and that spread is modelled with a Fisher distribution. The model is then constrained against measurements of the Pierre Auger Observatory, especially against its dipolar anisotropy. Under the small angle approximation, this gives the root mean square angular deflection with respect to the line of sight of 50 +11/-10 degrees. It is shown that the angular deflection would be even greater if particles were crossing different domains of a structured magnetic field. When applying this to two potential nearby sources, Cen A and the Virgo cluster, estimates between the coherence length and field strength are obtained for the intervening turbulent magnetic field.
In the second topic, effects of magnetic fields on anisotropies are considered by inspecting the applicability of Liouville's theorem on cosmic ray anisotropies. The concept of trapping was identified as a potential cause of anisotropies, and one case of its application is demonstrated. It is shown how the trapping in a structured field can generate a dipolar anisotropy.
The side topic explores the transition from the rectilinear to diffusive propagation where a precise criterion is derived for the case of a turbulent magnetic field
Simulating the Galactic multi-messenger emissions with HERMES
No full textContext. The study of nonthermal processes such as synchrotron emission, inverse Compton scattering, bremsstrahlung, and pion production is crucial to understanding the properties of the Galactic cosmic-ray population, to shed light on their origin and confinement mechanisms, and to assess the significance of exotic signals possibly associated to new physics.
Aims. We present a public code called HERME
Evidence for a mixed mass composition at the ‘ankle’ in the cosmic-ray spectrum
No full textWe report a first measurement for ultrahigh energy cosmic rays of the correlation between the depth of shower maximum and the signal in the water Cherenkov stations of air-showers registered simultaneously by the fluorescence and the surface detectors of the Pierre Auger Observatory. Such a correlation measurement is a unique feature of a hybrid air-shower observatory with sensitivity to both the electromagnetic and muonic components. It allows an accurate determination of the spread of primary masses in the cosmic-ray flux. Up till now, constraints on the spread of primary masses have been dominated by systematic uncertainties. The present correlation measurement is not affected by systematics in the measurement of the depth of shower maximum or the signal in the water Cherenkov stations. The analysis relies on general characteristics of air showers and is thus robust also with respect to uncertainties in hadronic event generators. The observed correlation in the energy range around the ‘ankle’ at lg(E/eV)=18.5–19.0lg(E/eV)=18.5–19.0 differs significantly from expectations for pure primary cosmic-ray compositions. A light composition made up of proton and helium only is equally inconsistent with observations. The data are explained well by a mixed composition including nuclei with mass A>4A>4. Scenarios such as the proton dip model, with almost pure compositions, are thus disfavored as the sole explanation of the ultrahigh-energy cosmic-ray flux at Earth
Movement
No full textMesh movement methods for finite element problems solved using Firedrake.If you use this software in a publication, please cite it using these metadata
Erratum: Search for photons with energies above 1018 eV using the hybrid detector of the Pierre Auger Observatory (Journal of Cosmology and Astroparticle Physics (2017) 4 (9) DOI: 10.1088/1475-7516/2017/04/009)
No full text1 Exposure calculation Due to a mistake in the numerical integration following eq. (6.2) of the original article [1], the exposure shown in figure 5 of the original article was incorrect. The correct exposure is shown in figure 1. 2 Upper limits on the integral photon flux and fraction The incorrect exposure affects the calculation of the upper limits on the integral photon flux following eq. (6.1) of the original article. The correct values for the upper limits are 0.038, 0.010, 0.009, 0.008 and 0.007 km−2 sr−1 yr−1 for threshold energies of 1, 2, 3, 5 and 10 EeV. The correct values for the upper limits on the integral photon fraction subsequently derived are 0.14 %, 0.17 %, 0.42 %, 0.86 % and 2.9 % for the same threshold energies. 3 Author list The author list of this erratum also corrects a mistake made in the original article, where F. Zuccarello was missing and Z. Zong was listed twice
Erratum: Search for photons with energies above 1018 eV using the hybrid detector of the Pierre Auger Observatory
No full textExposure calculation Due to a mistake in the numerical integration following eq. (6.2) of the original article [1], the exposure shown in figure 5 of the original article was incorrect. The correct exposure is shown in figure 1. 2 Upper limits on the integral photon flux and fraction The incorrect exposure affects the calculation of the upper limits on the integral photon flux following eq. (6.1) of the original article. The correct values for the upper limits are 0.038, 0.010, 0.009, 0.008 and 0.007 km−2 sr−1 yr−1 for threshold energies of 1, 2, 3, 5 and 10 EeV. The correct values for the upper limits on the integral photon fraction subsequently derived are 0.14 %, 0.17 %, 0.42 %, 0.86 % and 2.9 % for the same threshold energies. 3 Author list The author list of this erratum also corrects a mistake made in the original article, where F. Zuccarello was missing and Z. Zong was listed twice
CRPropa 3.2-an advanced framework for high-energy particle propagation in extragalactic and galactic spaces
No full textCRPropa 3 - a Public Astrophysical Simulation Framework for Propagating Extraterrestrial Ultra-High Energy Particles
No full textWe present the simulation framework CRPropa version 3 designed for efficient development of astrophysical predictions for ultra-high energy particles. Users can assemble modules of the most relevant propagation effects in galactic and extragalactic space, include their own physics modules with new features, and receive on output primary and secondary cosmic messengers including nuclei, neutrinos and photons. In extension to the propagation physics contained in a previous CRPropa version, the new version facilitates high-performance computing and comprises new physical features such as an interface for galactic propagation using lensing techniques, an improved photonuclear interaction calculation, and propagation in time dependent environments to take into account cosmic evolution effects in anisotropy studies and variable sources. First applications using highlighted features are presented as well
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