The role of AGN jets and intracluster magnetic fields in the formation and acceleration of cosmic rays

Using radio and X-ray data of two powerful radiogalaxies we attempt to find out the role that radio jets (in terms of composition and power) as well as intracluster magnetic fields play in the formation, propagation and acceleration of cosmic rays. For this study we have selected the powerful radio galaxies Hercules A and 3C\,310 because of the presence of ring-like features in their kpc-scale radio emission instead of the usual hotspots. These two FR1.5 lie at the center of galaxy cooling flow clusters in a dense environment. We observed the unique jets of Hercules both in kpc- (multifrequency VLA data) and pc-scales (EVN observations at 18 cm). We have also observed the core and inner jets of 3C310 at 18 cm using global VLBI. We report on the work in progress.Comment: 2 pages, IAU Conference No. 27

Extended reagions of radio emission not associated with the AGN phenomenon as sources of acceleration of cosmic rays: The case of cD galaxies

Diffuse, non-thermal extended emission not associated with the AGN phenomenon, found in many clusters of galaxies hosted by an AGN, are related to the acceleration of cosmic rays. In the current work we present preliminary evidence of absence of such formations in clusters of galaxies hosted by optically identified cD galaxies. Our subsample consists of three powerful low redshift radiogalaxies, centered in poor clusters of galaxies. We have searched for radio relics and (mini)halos which could be forming as a result of the confinement of cosmic rays by bubbles creayed by the AGN. We report on the work in progress.Comment: 4 pages, Conference HEPRO II

Implications of pc and kpc jet asymmetry to the cosmic ray acceleration

We probe the role that the directional asymmetry, between relativistic outflows and kilo-parsec scale jets, play in the acceleration of cosmic rays. For this reason we use two powerful, nearby Active Galactic Nuclei (AGNs). These radio galaxies are atypical compared to the usual AGN as they contain ring-like features instead of hotspots. Our VLBI radio data have revealed a substantial misalignment between their small and large scale jets. Taking into account the overall information we have obtained about the AGNs themselves (VLA and VLBI radio data at 18 cm) and their clusters (X-ray observations) our study supports the present ideas of powerful radiogalaxies (radio quiet and radio loud) being sources of cosmic rays as well as their ability to accelarate the latter to ultra high energies.Comment: 4 pages, Conference HEPRO II

Extended X-ray emission from radio galaxy cocoons

We study the emission of X-rays from lobes of FR-II radio galaxies by inverse Compton scattering of microwave background photons. Using a simple model that takes into account injection of relativistic electrons, their energy losses through adiabatic expansion, synchrotron and inverse Compton emission, and also the stopping of the jet after a certain time, we study the evolution of the total X-ray power, the surface brightness, angular size of the X-ray bright region and the X-ray photon index, as functions of time and cocoon size, and compare the predictions with observations. We find that the radio power drops rapidly after the stopping of the jet, with a shorter time-scale than the X-ray power. The X-ray spectrum initially hardens until the jet stops because the steepening of electron spectrum is mitigated by the injection of fresh particles, for electrons with $\gamma \ge 10^3$. This happens because of the concurrence of two times scales, that of the typical jet lifetimes and cooling due to inverse Compton scattering ($\sim 10^{7\hbox{--}8}$ yr), of electrons responsible for scattering CMB photons into keV range photons (with $\gamma \sim \sqrt{1 \, {\rm keV}/ kT_{CMB}}$). Another finding is that the ratio of the X-ray to radio power is a robust parameter that varies mostly with redshift and ambient density, but is weakly dependent on other parameters. We also determine the time-averaged ratio of X-ray to radio luminosities (at 1 keV and 151 MHz) and find that it scales with redshift as $\propto (1+z)^{3.8}$, for typical values of parameters. We then estimate the X-ray luminosity function of FR-II radio galaxies and estimate the number of these diffuse X-ray bright objects above a flux limit of $\sim 3 \times 10^{-16}$ erg cm$^{-2}$ s$^{-1}$ to be $\sim 25$ deg$^{-2}$.Comment: 9 pages, 5 figures, accepted for publication in MNRAS (replaced with final version to match the printed version

Orientation and size of the `Z' in `X'-shaped radio galaxies

Some X-shaped radio galaxies show a Z-symmetric morphology in the less luminous secondary lobes. Within the scenario of a merger between two galaxies, each hosting a supermassive black hole in its center, this structure has been explained before: As the smaller galaxy spirals towards the common center, it releases gas to the ISM of the larger active galaxy. The ram pressure of this streaming gas will bend the lobes of the pre-merger jet into a Z-shape. After the black holes have merged the jet propagates in a new direction that is aligned with the angular momentum of the binary black hole. In this article we deproject the pre- and post-merger jets. Taking into account the expected angles between the jet pairs and with the assumption that their directions are uncorrelated, we show that one of three possible orientations of the jets with respect to the line of sight is more likely than the others. This actually depends on the distance where the bending occurs. Another result of our deprojection is that the streaming gas bends the jet into a Z-shape in a range between about 30 and 100 kpc distance to the center of the primary galaxy. We confirm this finding by comparing our predictions for the properties of the rotational velocity field and its radius with observations and numerical simulations of merging galaxies. Thus our results support the merger scenario as explanation for X- and Z-shaped radio galaxies with the jet pointing along the former axis of orbital angular momentum of the binary.Comment: 11 pages, 6 figures, minor changes in final version. Accepted for publication in MNRA

Simulations of Hot Bubbles in the ICM

We review the general properties of the intracluster medium (ICM) in clusters that host a cooling flow, and in particular the effects on the ICM of the injection of hot plasma by a powerful active galactic nucleus (AGN). It is observed that, in some cases, the hot plasma produces cavities in the ICM that finally detach and rise, perhaps buoyantly. The gas dynamics induced by the rising bubbles can help explain the absence of a cooled gas component in clusters with a cooling flow. This scenario is explored using numerical simulations.Comment: 13 pages, no figures. Accepted for publication in Modern Physics Letters