Active Galactic Nuclei: Sources for ultra high energy cosmic rays?

Abstract

The origin of ultra high energy cosmic rays promises to lead us to a deeper understanding of the structure of matter. This is possible through the study of particle collisions at center-of-mass energies in interactions far larger than anything possible with the Large Hadron Collider, albeit at the substantial cost of no control over the sources and interaction sites. For the extreme energies we have to identify and understand the sources first, before trying to use them as physics laboratories. Here we describe the current stage of this exploration. The most promising contenders as sources are radio galaxies and gamma ray bursts. The sky distribution of observed events yields a hint favoring radio galaxies. Key in this quest are the intergalactic and galactic magnetic fields, whose strength and structure are not yet fully understood. Current data and statistics do not yet allow a final judgement. We outline how we may progress in the near future.

On ultra-high energy cosmic rays: Origin in AGN jets and transport in expanding universe

“…Simple estimates (Torres & Anchordoqui, 2004;Berezinskii et al, 1990) show that from the viewpoint of energetics the AGN jets can be the sources of ultra-high energy cosmic rays. Different aspects of particle acceleration in AGN jets were considered by Biermann & Strittmatter (1987); Norman et al (1995); Biermann et al (2008); Lemoine (2008); Pe'er et al (2009), see also references below.…”

Magnetic Fields of Nearby Active Galactic Nuclei and Correlation of the Highest-Energy Cosmic Rays with their Positions

“…We mean the process of generation of cosmic ray particles with ultra-high energy in a result of acceleration in jets and extended envelopes surrounding AGN. This scenario was recently developed by a number of authors (Dermer et al, 2008;Allard et al, 2008;Berezhko, 2008;Bierman et al, 2008). The decisive choice between various probable scenarios will be done in the result of future cosmic observations and move details confirmation of the Pierre Auger Collaboration data.…”

Mapping the most energetic cosmic rays

“…If the few brightest radio galaxies within ∼ 80 Mpc, notably M87 (Virgo A), Cen A and Fornax A, had been the dominant sources, their output must have been spread widely over the sky by magnetic deflections [4,5,6]. However, only a small proportion of such widely-scattered cosmic rays would line up within 3.2 • of a catalogued AGN, as pointed out in section 3: this is not the case.…”

“…First, regarding the methodology, it has been suspected that the apparent statistical significance of the result has been artificially generated by the use of the first half of the Auger observational data set to vary the selection "cuts" in energy threshold (57 EeV), maximum redshift of catalogued AGNs to be used in the correlation (< 0.018), and the correlation window size (3.2 • ): all chosen to maximize the significance of the departure from isotropy in this first subset. Several early discussions of the arrival directions have put aside the apparent close correlation with weak AGNs, and considered large magnetic displacements from the directions of expected strong sources [4,5,6]. The use of the VCV catalogue based on optical appearance of galaxies, rather than one with more emphasis on high jet luminosity indicated by strong radio or X-ray emission, has been questioned [7,8].…”

“…Their published study was intended to demonstrate anisotropy rather than to explain it at this stage.) Whilst the aim of the research is to understand how particles are accelerated to these extreme energies [4,5,12], the emphasis in this paper is on extracting as clearly as possible the simplest pointers to sources that are present in the cosmic-ray directional data, largely avoiding scrutiny of particular accelerators. When three times the presently published data set is available, it should be possible to pay attention to individual sources.…”