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Comptes Rendus Physique
Volume 15, n° 4
pages 339-348 (avril 2014)
Doi : 10.1016/j.crhy.2014.04.002
The Galactic magnetic field and ultrahigh-energy cosmic ray deflections
Le champ magnétique galactique et la déflexion des rayons cosmiques ultra-énergétiques
 

Glennys R. Farrar
 Center for Cosmology and Particle Physics, Department of Physics, New York University, USA 

Abstract

Our understanding of the Galactic magnetic field (GMF) has increased considerably in recent years, while at the same time remaining far from adequate. By way of illustration, the Jansson and Farrar (2012) (JF12) GMF model is described, emphasizing how it is constrained and which features are robust or likely to change, as modeling and constraining data improve. The most urgent requirements for the next phase of modeling are a more realistic model for the relativistic electron distribution (in order to reduce the systematic error associated with interpreting synchrotron data) and a better theoretical understanding of the origin of the large-scale coherent field (in order to develop a better phenomenological parameterization of the field). Even in its current stage of development, the JF12 model allows some important conclusions about UHECR deflections in the GMF to be formulated.

The full text of this article is available in PDF format.
Résumé

Notre compréhension du champ magnétique galactique (GMF) s'est considérablement améliorée au cours des dernières années, mais reste largement insuffisante. À titre d'illustration, le modèle GMF de Jansson et Farrar (2012) (JF12) est décrit ici, en insistant sur la manière dont il est contraint et sur ses caractéristiques, qu'elles soient robustes ou, au contraire, susceptibles de changer avec l'amélioration de la modélisation et des données. Les besoins les plus urgents pour la prochaine phase de modélisation sont, d'une part, un modèle plus réaliste de la distribution des électrons relativistes (ce qui permettra de réduire les incertitudes systématiques associées à l'interprétation des données d'émissions synchrotron) et, d'autre part, une meilleure compréhension théorique de l'origine du champ galactique cohérent sur les grandes échelles (afin de développer une meilleure paramétrisation phénoménologique du champs). Le modèle JF12, même dans sa version actuelle, permet de formuler quelques conclusions importantes sur la déflexion des RCUHE dans la Galaxie.

The full text of this article is available in PDF format.

Keywords : UHECR, Galactic magnetic field, Magnetic deflections

Mots-clés : RCUHE, Champs magnétique galactique, Déflexions magnétiques


1  Rigidity, energy divided by charge, is all that matters for cosmic ray deflections. Rigidity is properly measured in units of V but when only magnetic deflections and not energy losses are of concern, V and eV maybe used interchangeably since knowing the deflection of a proton of energy E in eV specifies the deflection of any CR with the same value of E /Z .
2  Using this technique, all-sky forward tracking in the JF12 regular-field at 0.1° resolution, for   from 0.0 to 2.0 in steps of size 0.01–0.05, and also with several different realizations of the random field for  , 1.0 and 1.5, has been performed. An online tool employing fast database techniques is available at Astroparticle, so a user can select sources and rigidities for forward-tracking. As the backtracking for new rigidities and fields are completed, the database will be updated. For further details, see [[22]].
3  Some events will have a more reliable rigidity determination than others, and the potential accuracy on the charge assignment will depend on the composition mix. For instance, if the composition were a simple mix of half proton and half iron, whose distributions of depth of shower maximum are very dissimilar, many events would have unambiguous charge assignments and source studies could be restricted to events whose deflections are well-determined. Independent of how simple or complex is the composition, as long as there is a protonic component some events will have such a deep   that they will be unambiguously identifiable, and among those the ones with small deflection uncertainties can be selected for correlation studies.


© 2014  Published by Elsevier Masson SAS de la part de Académie des sciences.
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