Ultra-high energy cosmic rays, spiral galaxies and magnetars

Abstract

We measure the correlation between the arrival directions of the highest energy cosmic rays detected by the Pierre Auger Observatory with the position of the galaxies in the HI Parkes All-Sky Survey (HIPASS) catalogue, weighted for their HI flux and Auger exposure. The use of this absorption-free catalogue, complete also along the Galactic plane, allows us to use all the Auger events. The correlation is significant, being 86.2 per cent for the entire sample of HI galaxies, and becoming 99 per cent when considering the richest galaxies in HI content or 98 per cent with those lying between 40 and 55 Mpc. We interpret this result as the evidence that spiral galaxies are the hosts of the producers of ultra-high energy cosmic rays and we briefly discuss the classical (i.e. energetic and distant) long gamma-ray burst (GRBs), short GRBs, as well as newly born or late-flaring magnetars as possible sources of the Auger events. With the caveat that these events are still very few, and the theoretical uncertainties are conspicuous, we found that newly born magnetars are the best candidates. If so, they could also be associated with sub-energetic, spectrally soft, nearby, long GRBs. We finally discuss why there is a clustering of Auger events in the direction on the radio galaxy Cen A and an absence of events in the direction of the radio galaxy M87. © 2008 The Authors. Journal compilation © 2008 RAS.