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We study particle acceleration and magnetic field amplification in the termination shocks (hotspots) of radiogalaxy jets. The cut-off of the synchrotron spectrum in the hotspots of powerful radiogalaxies is typically observed between infrared and optical frequencies, indicating that the maximum energy of non-thermal electrons accelerated at the jet termination shock is about 1 TeV for a canonical magnetic field of 100 μG. Based on theoretical considerations and observational data we show that the maximum energy of electrons cannot be constrained by synchrotron losses as usually assumed, unless the jet density is unreasonable large and most of the jet kinetic energy goes to non-thermal electrons. The maximum energy is ultimately determined by the ability to scatter particles back and forth the shock, and this limit applies to both electrons and protons. Therefore, the maximum energy of protons is also about 1 TeV when radiative cooling is not efficient. We show that non-resonant hybrid (Bell) instabilities generated by the streaming of cosmic rays can grow fast enough to amplify the jet magnetic field up to 100 μG and accelerate particles up to the maximum energies observed in the hotspots of radiogalaxies. [ABSTRACT FROM AUTHOR]

The origin of ultrahigh energy cosmic rays (UHECRs) is an open question. In this proceeding, we first review the general physical requirements that a source must meet for acceleration to 10-100 EeV, including the consideration that the shock is not highly relativistic. We show that shocks in the backflows of radio galaxies can meet these requirements. We discuss a model in which giant-lobed radio galaxies such as Centaurus A and Fornax A act as slowly-leaking UHECR reservoirs, with the UHECRs being accelerated during a more powerful past episode. We also show that Centaurus A, Fornax A and other radio galaxies may explain the observed anisotropies in data from the Pierre Auger Observatory, before examining some of the difficulties in associating UHECR anisotropies with astrophysical sources. [ABSTRACT FROM AUTHOR]

A detailed investigation of radio galaxies has recently stressed these sources as the possible origin of the cosmic rays observed above 3 EeV. Here, the relevance of this model at energies below 3 EeV is investigated. It is shown that the average contribution of radio galaxies can accurately explain the observed CR flux between the second knee and the ankle in the case of a strong source evolution. However, the model cannot provide the increasing heaviness and variance at energies ≲ 1 EeV of the observed chemical composition. In addition, it is exposed that the resulting variance of the chemical composition at Earth shows also at higher energies a clear disagreement with the observations, indicating that the compositional contributions by Centaurus A and Cygnus A need to be less different. [ABSTRACT FROM AUTHOR]

The Perseus cluster of galaxies with the central galaxy NGC 1275 is ideally suitable for studying both the physics of relativistic jets from Active Galactic Nuclei and for revealing the feedback role of the central galaxy. We present the results of fifteen-year-long observations of the AGN NGC 1275 at energies 800 GeV-40 TeV discovered by the SHALON telescope in 1996. The data obtained at very high energies by SHALON, namely the images of the galaxy and its surroundings, and the flux variability indicate that TeV γ -ray emission is produced by a number of processes: in particular, part of this emission is generated by relativistic jets in the nucleus of NGC 1275 itself. Unique data on GK Per(Nova 1901) and the IC 310 radio galaxy TeV γ -ray emission were obtained with the SHALON experiment for the first time. [ABSTRACT FROM AUTHOR]

NGC 1068, the brightest and closest Seyfert 2 galaxy, is the brightest of a handful of non-blazar galaxies observed to emit gamma-rays by the Fermi Gamma-ray Space Telescope[1]. We provide arguments for the hypothesis that galactic outflow driven by the active nucleus is the most likely source of both the radio and gamma-ray spectra and compare our results to other possible explanations including starburst activity and blazar-like jet emission. We finally outline a multi-wavelength observing program in progress to test this hypothesis. [ABSTRACT FROM AUTHOR]

The results of the analysis of Fermi-LAT data from seven years of observations of the broad line radio galaxy 3C 120 are presented. Compared with the previous studies, now the new PASS 8 data allows to investigate the temporal variability in long and short time scales. The temporal analysis indicates significant variability in short time scales. The spectral analysis is performed for the energies above 100 MeV and high energy γ-rays are detected up to 10 GeV. The γ- ray spectrum can be described as synchrotron self-Compton emission from the electron population producing radio-to-Xray emission in the jet. The required electron energy density exceeds the one of magnetic field, only by a factor of 2.6 meaning no significant deviation from equipartition. [ABSTRACT FROM AUTHOR]

We present the study of high energy γ-ray emission from NGC 1275 radio galaxy using seven years of public available Fermi-LAT data. The recent upgrade to new Pass 8 event-level analysis (with larger acceptance, a better angular and energy resolution and etc.) allows more detailed temporal and spectral analysis. The light cure with 7-day bins reveals several flaring activities, especially during the last two years of observation, when the weekly flux exceeds the averaged flux nearly 5 times. The flaring activities are investigated by the detected spectrum and temporal analysis. The spectral analysis indicates that in the flaring periods the power-law with exponential cut-off modeling is favored over the simple power-law models. The temporal analysis indicates a day scale variability of flux. [ABSTRACT FROM AUTHOR]

We present the results of a study aimed at evaluating the impact of the CTA in high-energy studies of radio galaxies, and elusive class of high-energy and very-high-energy emitters, which counts only 5 detections in the TeV band at the moment. We perform simulations of CTA observations of the Fermi-LAT radio galaxies using the ctools package. Our simulations indicate that 7 out of 12 local (z<0.1) candidates should be detected in 50 hours of CTA integration time, if the Fermi and the CTA powerlaws are smoothly connected. If the spectrum drops off in the TeV band, the number of detections progressively decreases shifting the power-law cut-off to lower energies. Given the elusiveness of radio galaxies at TeV energies, we suggest a CTA observing strategy based on long targeted observations. A blind-sky large area survey implies insufficient integrating time per FoV, but it will be suitable for discovering flaring sources or extremely high-energy peaked radio galaxies that are faint in the Fermi band (and therefore not part of the sample studied here) but observable in the TeV band. Finally we present a diagnostic plot useful to verify whether an AGN with given flux and power-law slope in the Fermi band could be a good target for CTA observations. [ABSTRACT FROM AUTHOR]

A radio core represents the peak of intensity in VLBI images and is located at the base of jets. It appears at different positions depending on frequencies. This is known as "core shift", caused by absorption of the core emission. The position of the central engine in an AGN can be estimated accurately by measuring the core shift with multifrequency and phase-referencing observations. We observed NGC 4261 using the VLBA at seven frequencies. This source is a nearby FR-I type radio galaxy at the distance of 30 Mpc and has prominent two-sided jets. We measured the core shifts in not only approaching side but also counter side of the jets. The positions of core at infinity of frequency in both side indicated to come close asymptotically to the same position, which was separated by 82±16 μas from 43 GHz core position, corresponding to 310±60 Rs (Schwarzschild radius). This source also has another feature that there is a region affected by free-free absorption (FFA) in the vicinity of the core and toward the counter jet. Moreover, we also found the same feature in other three sources, 3C 84, Cen A and Cyg A, which are also nearby galaxies with two-sided jets and with an indication of the FFA regions. We will measure the core shifts in these sources by using same technique as NGC 4261 in order to study the structure of circumnuclear plasma, to determine the position of the central engine and to test core shifts due to FFA. [ABSTRACT FROM AUTHOR]

Before the launch of the Fermi satellite only two classes of AGNs were known to produce relativistic jets and thus emit up to the γ-ray energy range: blazars and radio galaxies, both hosted in giant elliptical galaxies. The first four years of observations by the Large Area Telescope on board Fermi confirmed that these two are the most numerous classes of identified sources in the extragalactic γ-ray sky, but the discovery of γ-ray emission from 5 radio-loud narrow-line Seyfert 1 galaxies revealed the presence of a possible emerging third class of AGNs with relativistic jets. Considering that narrow-line Seyfert 1 galaxies seem to be typically hosted in spiral galaxy, this finding poses intriguing questions about the nature of these objects, the onset of production of relativistic jets, and the cosmological evolution of radio-loud AGN. Here, we discuss the radio-to-γ-rays properties of the γ-ray emitting narrow-line Seyfert 1 galaxies, also in comparison with the blazar scenario. [ABSTRACT FROM AUTHOR]

We review the gamma-ray variability properties of AGN with a jet not directly pointing at the observer, i.e. Misaligned AGN. This class is mainly populated by nearby low power radio galaxies (i.e. FRIs). The high power radio sources (i.e. FRIIs) are indeed rare in the GeV sky. Our Fermi-LAT inspection of 4 years of data reveals different temporal behaviors, supporting the idea that beaming/jet structural differences could characterize the FRI-FRII jets. The case of 3C111 (FRII) and NGC6251 (FRI) are treated in detail. New insights into the location and dimension of the gamma-ray dissipation regions are provided for galaxies with different radio morphologies. [ABSTRACT FROM AUTHOR]

Thanks to the Fermi γ-ray satellite, it is now confirmed that Misaligned Active Galactic Nuclei (MAGN), i.e. radio galaxies and steep spectrum radio quasars, are a new class of GeV emitters. In this work we present the first γ-ray and multiwavelength study of the two steep spectrum radio quasars, i.e. 3C 207 and 3C 380, belonging to the MAGN sample. From the γ-ray variability study we estimate the physical size of the zone where high-energy photons are dissipated: for both sources this region should be very compact, not larger than 0.05 pc. As a successive step, we build multiwavelength light curves of 3C 207 and 3C 380 to search for possible simultaneous outbursts in different wavebands with the aim of localizing the compact emitting region. This is an important issue with strong impact on theoretical models: indeed, knowing where high-energy photons are dissipated (at sub-pc or pc-scale) provides information on the nature of the seed photons involved in the production of the GeV radiation. [ABSTRACT FROM AUTHOR]

The giant radio galaxy M87 accompanies one of the nearest Active-Galactic-Nuclei jets showing the intense radiation through radio to TeV gamma-ray. Its proximity and the large mass of the central black hole provide an excellent advantage to probe the sites of jet formation and gamma-ray production. Here we review some of our recent studies for the inner jet of M87 based on the multi-frequency and multi-epoch VLBI observations, especially focusing on the two remarkable regions i.e., the jet base near the black hole and the peculiar feature HST-1. Our multi-frequency observations with the phase-referencing technique revealed the detailed structure of the jet base region regarding the location of the central engine and the collimation profile. In terms of HST-1, the intense multi-epoch VLBI monitoring constrained the accurate kinematic properties and the structural variations in this complicated feature, together with a possible connection to the gamma-ray activities. At the end of this contribution, we briefly describe our new monitoring project for M87 with VERA, which permits a detailed study on the structural evolution in the jet base region. [ABSTRACT FROM AUTHOR]

The detection of high-energy (HE) γ-ray emission up to ∼ 3 GeV from the giant lobes of the radio galaxy Centaurus A has been recently reported by the Fermi-LAT Collaboration based on ten months of all-sky survey observations. A data set more than three times larger is used here to study the morphology and photon spectrum of the lobes with higher statistics. The larger data set results in the detection of HE γ-ray emission (up to ∼ 6 GeV) from the lobes with a significance of more than 10 and 20 σ for the north and the south lobe, respectively. Based on a detailed spatial analysis and comparison with the associated radio lobes, we report evidence for a substantial extension of the HE γ-ray emission beyond the WMAP radio image for the northern lobe of Cen A. We reconstructed the spectral energy distribution (SED) of the lobes using radio (WMAP) and Fermi-LAT data from the same integration region. The implications are discussed in the context of hadronic and time-dependent leptonic scenarios. [ABSTRACT FROM AUTHOR]

Radio galaxies have emerged as a new gamma-ray emitting source class on the extragalactic sky. With their jets misaligned, i.e. not directly pointing towards us, they offer a unique tool to probe some of the fundamental (and otherwise hidden) non-thermal processes in AGN. This contribution briefly summarizes the observed characteristics of the four radio galaxies detected so far at very high energies (VHE). Given its prominence, particular attention is given to the origin of the variable VHE emission in M87. We discuss some of the theoretical progress achieved for this source within recent years highlighting, amongst others, the relevance of magnetospheric particle acceleration and emission models. [ABSTRACT FROM AUTHOR]

The populations of relativistic electrons and high-energy cosmic rays in the extended components of radio-loud active galaxies-kiloparsec-scale jets, hotspots and lobes-make them, in principle, interesting sources of gamma-ray photons up to the highest (TeV) energies. Here I discuss the few detections of extended gamma-ray emission with Fermi and show what constraints they put on the physical conditions in radio galaxies. Although detections of radio galaxies at TeV energy are rare, I show that the information we do have can already put interesting constraints on radio galaxy physics: the CTA should have the sensitivity and resolution to improve this situation considerably, and to resolve the expected arcmin-scale gamma-ray jet in the nearest radio galaxy, Centaurus A. Finally, I review the connection between the gamma-ray observations and the acceleration of ultra-high-energy cosmic rays, and suggest that, while radio galaxies may well be the sources of the highest-energy cosmic rays observed, they may constitute a 'disappointing' population in the sense that only very nearby sources, such as Cen A, will ever be identified as discrete cosmic-ray sources. [ABSTRACT FROM AUTHOR]

The giant radio galaxy M87 is located at a distance of 16.7Mpc and harbors a super-massive black hole (6 billion solar masses) in its center. M87 is one of just three radio galaxies known to emit TeV γ-rays. The structure of its relativistic plasma jet, which is not pointing towards our line of sight, is spatially resolved in X-ray (Chandra), optical and radio (VLA/VLBA) observations. The mechanishm and location of the TeV emitting region is one of the least understood aspects of AGN. In spring 2008 and 2010, the three TeV observatories VERITAS, MAGIC and H.E.S.S. detected two major TeV flares in coordinated observations. Simultaneous high-resolution observations at other wavelengths - radio (2008) and X-rays (2008/2010) - gave evidence that one of the TeV flares was related to an event in the core region; however, no common/repeated patterns could be identified so far. VERITAS continued to monitor M87 in 2011/2012. The results of these observations are presented. [ABSTRACT FROM AUTHOR]

Approximately 90 contributions to the 5th Heidelberg Symposium on High-Energy Gamma-Ray Astronomy (Gamma 2012), presented new results and ideas in the general field of extragalactic high-energy gamma-ray astronomy. The largest contingent of contributions in this field related to active galactic nuclei (AGN), including blazars, radio galaxies, and Narrow-Line Seyfert 1 (NLSy1) galaxies. Also, new results concerning starburst galaxies, as well as (so far) unsuccessful searches for γ-ray emission from other types of extragalactic sources have been reported. Finally, controversial discussions about studies of the γγ absorption imprint of the extragalactic background light on γ-ray emission from blazars, and potential implications for the intergalactic magnetic field have been discussed. This paper will provide a brief summary of the results and ideas on these topics, presented and discussed at Gamma 2012. [ABSTRACT FROM AUTHOR]

The recent discovery by Fermi/LAT of high-energy (E > 100MeV) γ rays from Narrow-Line Seyfert 1 Galaxies (NLS1s) made evident the existence of a third class of γ-ray emitting Active Galactic Nuclei (AGN), after blazars and radio galaxies. It is now possible to study a rather unexplored range of low masses (106-8 M⊙) and high accretion rates (up to the Eddington limit) of AGN with relativistic jets. A comparison with the jet emission from Galactic compact objects shows some striking similarities, indicating that NLS1s are the low-mass counterpart of blazars as neutron stars are the low-mass jet systems analogue of stellar mass black holes. [ABSTRACT FROM AUTHOR]

The Perseus cluster of galaxies is a nearby cool-core cluster with an intra-clustermedium (ICM) characterized by very high central densities. The observation of the Perseus cluster with the MAGIC telescopes, during 85 h from 2009 to 2011, resulted in the discovery of 2 point-like sources at very high energy (>100 GeV, VHE) coinciding with the central radio galaxy NGC1275 and the radio galaxy IC310. The γ-ray properties of these 2 sources are presented, taking into account contemporaneous Fermi-LAT as well as multi-wavelength data. Flux variability and spectral energy distribution shapes indicate that the VHE γ-rays do not originate from large-scale interaction of the radio galaxies with ICM but more likely from the active nuclei of these two galaxies. They could be both misaligned version of BL Lac objects, the most common TeV AGN. Our results provide vital clues to understand emission mechanisms of such misaligned objects, and how they may be related to the beamed emission seen in BL Lacs. No evidence of large-scale VHE γ-ray emission from hadronic cosmic ray (CR) interactions with the ICM has been found. The flux upper limit above 1 TeV reaches the signal expected by some theoretical models, constraining the cluster CR physics. In the framework of the hadronicmodel of the radiomini-halos, this limit implies aminimal magnetic field ranging from 4-9μG for the central cluster region. [ABSTRACT FROM AUTHOR]

Suzaku observations are reported of the three giant radio galaxies, 3C 35, 3C 326, and DA 240, with a projected linear size of >= 1 Mpc. The low and stable instrumental background of the X-ray Imaging Spectrometer onboard Suzaku allows a significant detection of inverse Compton X-ray emission from the lobes of these giant radio galaxies. As a result, the electron and magnetic energy densities in the lobes were measured. Based on the measurements, the late phase in the evolution of the energetics associated with jets from active galactic nuclei was investigated. It is found that the lobes of giant radio galaxies tend to reside in a near equipartition condition between electrons and magnetic field, despite the fact that smaller sources with sizes of about 100 kpc exhibit a particle dominance by a typical factor of 10 in energy density. In addition, the energy densities in the giant lobes are measured to be smaller by an order of magnitude as compared to the extrapolation of the size to energy density correlation found for smaller radio galaxies. These results indicate that typical radio galaxies experience a significant reduction in their jet power, as their jets evolve in size from 100 kpc to 1 Mpc. [ABSTRACT FROM AUTHOR]

The conditions within the giant lobes of Centaurus A are reviewed in light of recent radio and γ-ray observations. Data from WMAP and ground-based telescopes in conjunction with measurements from Fermi-LAT constrain the characteristic field strength and the maximum electron energy. The implications for the transport of energetic particles are discussed in terms of residence times and cooling times within the lobes. Acceleration of electrons and UHECR via the second order Fermi mechanism is discussed. [ABSTRACT FROM AUTHOR]

A checklist of criteria is presented to help establish the sources of ultra-high energy cosmic rays (UHECRs). These criteria are applied to long-duration GRBs in order to determine if they are UHECR sources. The evidence seems to favor blazars and radio galaxies (or other sources) over GRBs. [ABSTRACT FROM AUTHOR]

We present an ongoing, low-frequency radio/X-ray study of 18 nearby galaxy groups, chosen for the evidence, either in the X-ray or radio images, of AGN/intragroup gas interaction. We have obtained radio observations at 235 MHz and 610 MHz with the Giant Metrewave Radio Telescope (GMRT) for all the groups, and 327 MHz and 150 MHz for a few. We present results of the recent Chandra/GMRT study of the interesting case of AWM 4, a relaxed poor cluster of galaxies with no evidence of a large cool core and no X-ray cavities associated with the central radio galaxy. Our analysis shows how joining low-frequency radio data (to track the history of AGN outbursts) with X-ray data (to determine the state of the hot gas, its disturbances, heating and cooling) can provide a unique insight into the nature of the feedback mechanism in galaxy groups. [ABSTRACT FROM AUTHOR]

As a part of an ongoing study of a sample of galaxy groups showing evidence for AGN/hot gas interaction, we report on the preliminary results of an analysis of Chandra, XMM-Newton and new GMRT data of the X-ray bright compact group HCG 62. This is one of the few groups known to possess very clear, small X-ray cavities in the inner region as shown by the existing Chandra image. At higher frequency (1.4 GHz) the cavities show minimal if any radio emission, but the radio appears clearly at lower frequencies (<=610 MHz). We find that the radio source is radiatively inefficient, with a ratio of mechanical cavity power to radio luminosity of ∼104, and that the jets have hadronic content. We also identify a shock front located around 35 kpc to the south-west of the group center. Such a shock may have significantly heated the gas close to the southern cavity, as indicated by the temperature map. [ABSTRACT FROM AUTHOR]

H.E.S.S. is an array of four imaging atmospheric Cherenkov telescopes situated in the Khomas highlands in Namibia. Due to its large field of view, good angular resolution and excellent sensitivity it is ideally suited to detect VHE γ-ray sources. The Galactic plane survey and dedicated observations in pointing mode have led to the discovery of many previously unknown VHE γ-ray sources—galactic and extragalactic alike, including new classes of sources such as starburst galaxies. Beside the discovery potential, H.E.S.S. excels at morphological studies as well as the measurement of (spatially resolved) spectra and lightcurves down to a few minute timescales, thereby fostering the investigation of the underlying processes and emission mechanisms in the observed objects. [ABSTRACT FROM AUTHOR]

The 17 m diameter MAGIC telescope, located on the Canary island of La Palma, is the largest single-dish Cherenkov telescope for unveiling the gamma-ray universe. It reaches the lowest energy threshold among ground-based gamma-ray observatories: 55 GeV for normal observations, and as low as 25 GeV using a dedicated trigger system developed for pulsar observations. MAGIC also features a unique fast follow-up capability for tracking transients like gamma-ray bursts. Since Fall 2004 MAGIC has been taking data routinely, successfully detecting different classes of VHE sources like pulsar wind nebulae, gamma-ray binaries, pulsars, active galactic nuclei and radio galaxies. Here we review some of the most relevant results from recent observations, and report about the status of MAGIC-II, a stereoscopic extension by a second 17-m telescope already in operation. [ABSTRACT FROM AUTHOR]

We propose a new approach to estimate galaxy morphologies using a two-dimensional approach based on an ellipticity ([variant_greek_epsilon]) vs. Bulge-to-Total ratio (B/T) plane. We have calibrated this plane by comparing with Dressler’s classifications [5]. With the aid of our calibration, we have classified 635 galaxies in 18 Abell clusters (0.02R<-24.5 mag. If we believe Ferrarese & Merrit’s relation [6], these radio sources have 108–109 M⊙ black holes. [ABSTRACT FROM AUTHOR]

We present observational constraints on how AGN may regulate the thermal and dynamical state of the interstellar medium in radio galaxies at low and high redshift, and thus star formation and galaxy growth. Radio galaxies at z∼2 reveal energetic, extended outflows of few ×1010 M⊙ of warm ionized gas with kinetic energies near the binding energy of a massive galaxy, and a remarkable deficit in cold molecular gas. This suggests that powerful AGN feedback may terminate the active phase of growth of massive galaxies as postulated by models of galaxy evolution. On the example of a nearby radio galaxy we investigate how the AGN may affect the cold/warm ISM. 3C326 N at z = 0.1 is rich in molecular gas but the Schmidt-Kennicutt diagram suggests a much lower star-formation efficiency than in ‘normal’ galaxies. Most of the molecular gas is warm and appears heated by shocks on timescales of few ×104 yrs, shorter than the free-fall time of molecular clouds. We find a fast outflow of warm neutral gas which cannot be driven by star formation or the radiative energy of the AGN. Long dissipation times suggest these conditions will be maintained for 107–8 yrs. We relate these properties to the radio source through an extended ’cocoon model’ and discuss how our observations of radio-loud AGN at low and at high-z may help to better understand the role of AGN feedback for the evolution of massive galaxies across cosmic time. [ABSTRACT FROM AUTHOR]

In our ongoing multi-wavelength study of cluster AGN, we find ≈75% of the spectroscopically identified cluster X-ray point sources (XPS) with L0.3–8.0 keV>1042 ergs s-1 and cluster radio galaxies with P1.4 GHz>3×1023 W Hz-1 in 11 moderate redshift clusters (0.2L* possess relativistic jets which can inject energy into the ICM, potentially solving the uniform heating problem in the central region of clusters. [ABSTRACT FROM AUTHOR]

Following the Hart et al. contribution to this volume, we use the results of her survey to speculate that: (1) Virtually all bright cluster red sequence (CRS) elliptical galaxies in the inner regions (≤500 kpc from the center) of rich clusters are low-luminosity BL Lac Objects with relativistic jets; (2) These low-luminosity AGN may dominate the heat input into the intracluster medium; and (3) While Bondi accretion of ICM gas can explain the central concentration of these AGN, several aspects of non-BCG AGN cast doubt on whether or not gas accretion powers these sources. [ABSTRACT FROM AUTHOR]