The Galactic magnetic field and Centaurus A as a UHECR source

by Ronnie Jansson (New York University)

Friday 8 Jan 2010, 10:30 → 12:00 Europe/Stockholm

C61

I will present a new method to quantify the quality-of-fit between data and observables depending on the large-scale Galactic magnetic field (GMF). We combine WMAP5 polarized synchrotron data and Rotation Measures of extragalactic sources in a joint analysis to obtain best fit parameters and confidence levels for GMF models common in the literature. None of the existing models provide a good fit in both the disk and halo regions, and in many instances best-fit parameters are quite different than the original values. We improve the determination of the large scale GMF in the direction of the nearby radio galaxy Centaurus A, in order to decide whether Cen A can be responsible for the excess of Ultrahigh Energy Cosmic Rays (UHECRs) in that region observed by the Pierre Auger Observatory. We find that at most 4-5 of the published 27 Auger events above 57 EeV are consistent with coming from Cen A and its radio lobes, if the CRs are protons. More generally, we show that independently of their composition, UHECRs from Cen A should appear in a swath of <50 degrees opening angle from Cen A toward the Galactic plane, contrary to the observed excess.