The Galactic magnetic field and propagation of ultra-high energy cosmic rays

Abstract

Abstract. The puzzle of ultra-high energy cosmic rays (UHECRs) still remains unresolved. With the progress in the preparation of the next generation of experiments (AUGER, EUSO, OWL), the importance of directional analysis of existing and future events is increasing. The Galactic Magnetic Field (GMF) plays the key role in source identification even in this energy range. We first analyze the current status of our experimental and theoretical knowledge about the GMF and introduce a complex up-to-date model of GMF. Then we present two examples of simple applications of the influence of the GMF on UHECR propagation. Both examples are based on the Lorentz equation solution. The first one is a basic directional analysis of the incident directions of UHECRs and the second one is a simulation of a change of chemical composition of CRs in the energy range 10 13 ÷ 10 19 eV. The results of these simple analyses are surprisingly rich -e.g. the rates of particle escape from the Galaxy or the amplifications of particle flux in specific directions.

The Galactic magnetic field as spectrograph for ultra-high energy cosmic rays

“…In the slightly modified version we use here, we fix z 0 = 0.2 kpc, p = −8 • , d = −0.5 kpc and normalize the local field to 2 µG. Apart for the larger field-strength, the main difference with the TT model is the parity of the disk field, which we take here to be even as in [34]. Additionally, we consider a toroidal thick disk/halo contribution,…”

Ultra-high energy cosmic rays detected by Auger and AGASA

“…Given the measurement of a non-zero vertical (z) component of the GMF, in both the Galactic center and the Solar vicinity, a dipole field model is usually added to the toroidal field above. Detailed descriptions and discussions of these GMFs can be found in Stanev (1997), Beck (2001), Han (2002), Tinyakov & Tkachev (2002), Prouza & Šmída (2003), Brown et al (2007), Kachelrieß et al (2007), Men et al (2008), Takami &Sato (2008), andHan (2009). For these four models, we use the equations and their related normalizations following Takami & Sato (2008), and always include the dipole field component as specified in Takami & Sato (2008).…”

“…The modified BS-S model is based on the traditional BS-S model but with different parameters and normalizations. The three new models presented by S08 also include a toroidal halo field as presented initially in Prouza & Šmída (2003), but do not include a dipole magnetic field component. We use these three models and their related halo field described in S08 with only one difference: in the AS-S+ARM model, we directly use the log spiral arm morphology described in Wainscoat et al (1992) without correcting for their shape close to the solar neighbourhood as in S08, who used the correction suggested in Taylor & Cordes (1993).…”

“…Finally, we added a turbulent field component. The turbulent field component was computed following the recipe described in Prouza & Šmída (2003) with slightly different normalization parameters: the maximum turbulent magnetic field strength in each cartesian component was taken to be ±10 μG, and the probability of a turbulent field being present was taken to be 1% in the halo of the Galaxy, 20% in the disk of the Galaxy (Galactic radius less then 20 kpc and Galactic height less than 1.5 kpc) and 80% in the spiral arms of the Galaxy -where we used the spiral arm definition from Wainscoat et al (1992), spiral arm thickness 0.75 kpc in the disk (i.e., coordinate r), and half-height 0.5 kpc (coordinate z). We therefore generated a random number to determine whether a turbulent field should be added following the probabilities above.…”

Analytical models of X-shape magnetic fields in galactic halos

“…Now the question that naturally comes to mind is whether the halo of our own Galaxy also possesses an X-shape magnetic field. The most widely used description of the Galactic halo field relies on the double-torus picture, originally sketched by Han (2002) and later modeled by Prouza & Šmída (2003); Sun et al (2008); Jansson & Farrar (2012a), where the halo field is purely azimuthal, forms a torus on each side of the Galactic plane and has opposite signs above and below the plane. For the first time, Jansson & Farrar (2012a,b) added to this double-torus component a simple X-shape component, which they chose to be axisymmetric and purely poloidal 1 .…”