Heavy Cosmic Ray Nuclei from Extragalactic Sources above ‘The Ankle '

Abstract

A recent observation by the Auger Observatory group presents evidence for cosmic rays above 5.6 10 19 eV -(56 EeV) being 'predominantly protons' coming from Active Galactic Nuclei. If, as would be expected, the particles above the ankle at about 2 EeV are almost all of Extragalactic origin then it follows that the characteristics of the nuclear interactions of such particles would need to be very different from conventional expectation -a result that follows from the measured positions of 'shower maximum' at somewhat lower energies where mass measurements using conventional nuclear interaction models indicate (ln A)≃ 2.5. Such a claim is rather dramatic.In our own analysis we study to what extent the Auger results could, indeed, give such a mean value for (ln A)rather than a much smaller one. We conclude that they can, and the need for a dramatic change in the nuclear physics disappears.PACS numbers: 96.50.sb, 96.50.sd, 98.70.Sa.

Galactic magnetic deflections and Centaurus A as a UHECR source

“…The possibility that Cen A could in fact be the source of most cosmic rays, if turbulent extragalactic magnetic fields on the Cen A side of the Milky Way are near the maximum allowed value, was first proposed by Farrar and Piran [5]. Some of the more recent works include: [7], which proposes that Cen A is one of three sources that, combined, are responsible for all observed UHECRs; [8] which analyzes the significance of correlation between UHECRs and Cen A; [9] which investigates the plausibility of the giant radio lobes of Cen A being acceleration sites of UHECRs; [10] which considers the possibility that the radio jet at the core of Cen A is an accelerator; [11,29] which considers various mechanisms that could accelerate UHECRs in radio galaxies such as Cen A; and [12,13] which argue that Cen A is the source of the ≈ 10 events in the region of the sky surrounding Cen A. Ref. [30] notes that Cen A could be associated with at least 4 out of the -at the time -27 published Pierre Auger UHECRs above 57 EeV due to its large radio extent, but does not consider the deflection by any particular Galactic magnetic field model.…”

“…Tantalizingly, the highest energy Pierre Auger Observatory events show a distinct excess within 18 • of Cen A: 13 events observed, while 3.2 events would be expected for 69 events coming from an isotropic distribution [6]. This excess has re-ignited interest in the possibility that Cen A is the source of most of these events [7][8][9][10][11][12][13]. However, Cen A is located in the "Supergalactic Plane" -a nearby overdensity of galaxies -so the UHECR excess could be produced by multiple sources in the general region, or possibly simply be due to some focussing effect of the GMF or EGMF.…”

A lepto-hadronic model for high-energy emission from FR I radiogalaxies

“…Recently, the Pierre Auger Collaboration reported the existence of anisotropy on the arrival directions of UHE cosmic rays (Abraham et al 2007), remarking that at least 2 of this events can be correlated with the Cen A position (3 • circle). Further works have claimed that there are several events that can be associated with Cen A and its big radio lobes (Gorbunov et al 2008;Fargion 2008;Wibig & Wolfendale 2007) but this correlation is still statistically weak.…”

Update on the correlation of the highest energy cosmic rays with nearby extragalactic matter

“…Moreover, active galaxies in this catalog trace the nearby large-scale matter distribution, and that includes all types of candidate astrophysical sources, not only AGNs and their subclasses. Analyses comparing the Auger data reported in [6,7] with different types of nearby extragalactic objects can be found in [12][13][14][15][16][17][18][19][20][21][22].…”