Galactic magnetic deflections and Centaurus A as a UHECR source

TL;DR

This study assesses Galactic magnetic field models, especially Jansson-Farrar 2012, for predicting ultra-high-energy cosmic ray deflections from Centaurus A, confirming some events could originate there with minimal deflection.

Contribution

It validates the Jansson-Farrar 2012 Galactic magnetic field model for UHECR deflection predictions near Centaurus A, supporting its use in cosmic ray origin studies.

Findings

Up to six UHECR events above 55 EeV could originate from Cen A with deflections less than 18 degrees.

The JF12 model accurately predicts magnetic deflections in the Cen A region, matching observations.

A strong extragalactic magnetic field (>80 nG) would be needed to significantly alter the results.

Abstract

We evaluate the validity of leading models of the Galactic magnetic field for predicting UHECR deflections from Cen A. The Jansson-Farrar 2012 GMF model (JF12), which includes striated and random components as well as an out-of-plane contribution to the regular field not considered in other models, gives by far the best fit globally to all-sky data including the WMAP7 22 GHz synchrotron emission maps for Q, U, and I and ~40,000$ extragalactic Rotation Measures (RMs). Here we test the models specifically in the Cen A region, using 160 well-measured RMs and the Polarized Intensity from WMAP, nearby but outside the Cen A radio lobes. The JF12 model predictions are in excellent agreement with the observations, justifying confidence in its predictions for deflections of UHECRs from Cen A. We find that up to six of the 69 Auger events above 55 EeV are consistent with originating in Cen A and being deflected <18 degrees; in this case three are protons and three have Z=2-4. Others of the 13 events within 18 degrees must have another origin. In order for a random extragalactic magnetic field between Cen A and the Milky Way to appreciably alter these conclusions, its strength would have to be > ~ 80 nG -- far larger than normally imagined.