arXiv:1109.1703v1 [astro-ph.CO] 8 Sep 2011 On the origin and acceleration of ultra high energy cosmic rays: Cooling flow clusters and AGN hosts ∗ Gizani, Nectaria A. B. † Abstract We are looking for radio ‘relics’ and ‘halos’ in an X-ray selected sample of clusters of galaxies. These radio features are not a product of the Active Galactic Nuclei (AGN)-mechanism, but more likely are associated with past cluster merger events. AGN hosts of cooling flow clusters contain particle bubbles that show non-thermal radio emission. These bubbles could explain the presence of radio relics and halos if they can restrict cosmic rays efficiently. Intracluster magnetic fields and cluster environments can reveal the acceleration mechanisms of cosmic rays. Using radio/X-ray data and analytical methods we examine three AGN hosts out of our 70 clusters, namely Hercules A, 3C310 and 3C388. We found that none of these clusters contain relics and/or halos. Keywords: AGN, Synchrotron emission, Cooling flows, Individual clusters of galaxies, Cosmic Rays (UHECRs), accel- eration mechanisms 1 Introduction Ultra-high energy cosmic rays (UHECR) detected by the Pierre Auger and other cosmic ray Observatories suggest that they can be accelerated in the active galactic nuclei (eg. [2, 4]) , in shocks, formed as the jets continuously feed the lobes with new material (eg. [2, 16]), and in turbulent magnetized plasma in the jets and/or lobes of radio galaxies. This suggests that super-massive black holes at the centers of FR I and II radiogalaxies can produce high energy particles. Sub-parsec scale acceleration is efficient as long as the scales are comparable to the scale of jet generation or initial collimation. Hardcastle [10] suggests that stochastic particle acceleration of UHECRs to high energies (10 20 eV) is possible within the large-scale lobes of powerful radiogalaxies as long as the radio sources are at low redshift. Enβlin et al., [5] concluded that radio galaxies are powerful enough to heat and support the cluster gas with injected cosmic-ray protons and magnetic field densities (permitted by Faraday rotation and gamma-ray observations of galaxy clusters) within a cluster radius of ∼ 1 Mpc. Energy input in the intracluster medium (ICM) heats the gas, and injects cosmic rays (CRs) and magnetic fields. These are the three constituents of ICM, i.e. relativistic particles (CRs), weak magnetic fields (order of ∼ µG) and gas, which is detected in the X-rays. Haloes, relics and minihalos are structures of diffuse low surface non-thermal radio emission of relativistic particles spiraling intracluster magnetic fields. They are not directly associated with the AGN phenomenon or the galaxies of the cluster themselves. Their origin is thought to lie in the re-acceleration of relic population of relativistic electrons, or proton proton collisions with the ICM (e.g. [6]). We search for these structures in a sample of 70 Abell clusters. The sample was selected upon the radio to X-ray correlation. Our scope is to probe the role that cluster magnetic fields (via Faraday rotation and Inverse Compton Radiation arguments), merger events (through radio/X-ray interactions), cooling flow phenomena, jets, shocks, and nonthermal radio bubbles play in the production, acceleration and propagation of cosmic rays. In the current paper we present the study of three powerful AGN from our sample. These radiogalaxies (RGs) are situated at the center of dense galaxy cluster environments called ’Hercules A’, ’3C 388’ and ’3C 310’-cluster named after their hosts. Hercules A: 3C 348, or Her A is optically identified with a cD galaxy at z=0.154, the dimmer and bigger of the two galaxies, at the centre of a poor cluster. It is the fourth brightest radiogalaxy in the sky at low frequencies. Its radio power at 178 MHz is P AGN 178MHz = 19 × 10 26 W Hz −1 sr −1 . Although it is a high luminosity source, its structure resembles that of low luminosity Fanaroff-Riley class I objects, no hotspots and brightened edges (typical of FR IIs). These characteristics classify the radio source as an FR1/2. Its unusual jet dominated morphology presents interesting differences: helical structures in the eastern jet and striking ring-like features in the western one [3]. HST data suggest possible kiloparsec rings of obscuration, aligned near the radio axis with a slight offset from the galaxy nucleus [1]. 3C 388: The optical galaxy (z = 0.0908) is one of the brightest cDs. In the radio is a relatively small classical double FRII. Its radio power is P AGN 178MHz = .48 × 10 26 W Hz −1 sr −1 at 178 MHz. Its faint halo in the eastern lobe with steep spectrum and high polarization, and the relic of an older jet activity are associated with the individual galaxy rather than the cluster as a whole. The western side presents a similar low surface radio emission. There is a luminous jet contained within the western lobe and a possible counter-jet [18]. * Published in NIMA, doi:2010-12-018 † Hellenic Open University, School of Natural Sciences & Technology, Physics Laboratory, Tsamadou 13-15 & Ag. Andreou, 26222 Patra 1