Here we present a new approach for constraining luminous blazars, incorporating fully time-dependent and self-consistent modeling of bright gamma-ray flares of PKS1510-089 resolved with Fermi-LAT, in the framework of the internal shock scenario. The
results of our modeling imply the location of the gamma-ray flaring zone outside of the broad-line region, namely around 0.3pc from the core for a free-expanding jet with the opening angle Gamma, theta_mathrm{jet} simeq 1 (where Gamma is the jet bulk Lorentz factor), up to simeq 3pc for a collimated outflow with Gamma, theta_mathrm{jet} simeq 0.1. Moreover, under the Gamma, theta_mathrm{jet} simeq 1 condition, our modeling indicates the maximum efficiency of the jet production during the flares, with the total jet energy flux strongly dominated by protons and exceeding the available accretion power in the source. This is in contrast to the quiescence states of the blazar, characterized by lower jet kinetic power and an approximate energy equipartition between different plasma constituents. We demostrate how strictly simultaneous observations of flaring PKS1510-089 at optical, X-ray, and GeV photon energies on hourly timescales, augmented by extensive simulations as presented in this paper, may help to impose further precise constraints on the magnetization and opening angle of the emitting region. Our detailed modeling implies in addition that a non-uniformity of the Doppler factor across the jet, caused by the radial expansion of the outflow, may lead to a pronounced time distortion in the observed gamma-ray light curves, resulting in particular in asymmetric flux profiles with substantially extended decay phases.
We performed a systematic X-ray study of eight nearby gamma-ray bright radio galaxies with Suzaku for understanding the origin of their X-ray emissions. The Suzaku spectra for five of those have been presented previously, while the remaining three (M
87, PKS0625-354, and 3C78) are presented here for the first time. Based on the Fe-K line strength, X-ray variability, and X-ray power-law photon indices, and using additional information on the [O III] line emission, we argue for a jet origin of the observed X-ray emission in these three sources. We also analyzed five years of Fermi Large Area Telescope (LAT) GeV gamma-ray data on PKS0625-354 and 3C78 to understand these sources within the blazar picture. We found significant gamma-ray variability in the former object. Overall, we note that the Suzaku spectra for both PKS0625-354 and 3C78 are rather soft, while the LAT spectra are unusually hard when compared with other gamma-ray detected low-power (FR I) radio galaxies. We demonstrate that the constructed broad-band spectral energy distributions of PKS0625-354 and 3C78 are well described by a one-zone synchrotron/synchrotron self-Compton model. The results of the modeling indicate lower bulk Lorentz factors compared to those typically found in other BL Lac objects, but consistent with the values inferred from modeling other LAT-detected FR,I radio galaxies. Interestingly, the modeling also implies very high peak ($sim 10^{16}$ Hz) synchrotron frequencies in the two analyzed sources, contrary to previously-suggested scenarios for FR I/BL Lac unification. We discuss the implications of our findings in the context of the FR I/BL Lac unification schemes.
Many luminous blazars which are associated with quasar-type active galactic nuclei display broad-band spectra characterized by a large luminosity ratio of their high-energy (gamma-ray) and low-energy (synchrotron) spectral components. This large rati
o, reaching values up to 100, challenges the standard synchrotron self-Compton models by means of substantial departures from the minimum power condition. Luminous blazars have also typically very hard X-ray spectra, and those in turn seem to challenge hadronic scenarios for the high energy blazar emission. As shown in this paper, no such problems are faced by the models which involve Comptonization of radiation provided by a broad line-region, or dusty molecular torus. The lack or weakness of bulk Compton and Klein-Nishina features indicated by the presently available data favors production of gamma-rays via up-scattering of infrared photons from hot dust. This implies that the blazar emission zone is located at parsec-scale distances from the nucleus, and as such is possibly associated with the extended, quasi-stationary reconfinement shocks formed in relativistic outflows. This scenario predicts characteristic timescales for flux changes in luminous blazars to be days/weeks, consistent with the variability patterns observed in such systems at infrared, optical and gamma-ray frequencies. We also propose that the parsec-scale blazar activity can be occasionally accompanied by dissipative events taking place at sub-parsec distances and powered by internal shocks and/or reconnection of magnetic fields. These could account for the multiwavelength intra-day flares occasionally observed in powerful blazars sources.
(Abridged) Data collected by the Pierre Auger Observatory (Auger) provide evidence for anisotropy in the arrival directions of cosmic rays (CRs) with energies >57 EeV that suggests a correlation with the positions of AGN located within ~75 Mpc. A det
ailed study of the sample of AGN whose positions are located within 3.2 degrees of the CR events (and extending our analysis out to ~150 Mpc) shows that most of them are classified as Seyfert 2 and low-ionization nuclear emission-line region (LINER) galaxies whose properties do not differ substantially from other local AGN of the same types. Therefore, if the production of the highest energy CRs is persistent in nature, i.e., operates in a single object on long (>Myr) timescales, the claimed correlation between the CR events observed by Auger and local active galaxies should be considered as resulting from a chance coincidence. Additionally, most of the selected sources do not show significant jet activity, and hence, in most conservative scenarios, there are no reasons for expecting them to accelerate CRs up to the highest energies, ~10^20 eV. A future analysis has to take into account AGN morphology and may yield a correlation with a larger deflection angle and/or more distant sources. We further argue that the nearby radio galaxy NGC 5128 (Cen A) alone could be associated with at least 4 events due to its large radio extent, and PKS 1343-60 (Cen B), another nearby radio galaxy, can be associated with more than 1 event due to its proximity to the Galactic plane and, correspondingly, the stronger Galactic magnetic field the UHECRs encounter during propagation to the Earth. Future gamma-ray observations (by, e.g., Fermi Gamma-ray Space Telescope, and HESS) may provide additional clues to the nature of the accelerators of the UHECRs in the local Universe.
