Suzaku Observations of gamma-Ray Bright Radio Galaxies: Origin of the X-ray Emission and Broad-Band Modelin

Abstract

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 (M87, 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.

23 pages, 8 figures, accepted by ApJ

References in corpus (11)

• Hot and cold gas accretion and feedback in radio-loud active galaxies
• Fast variability of TeV gamma-rays from the radio galaxy M 87
• Synchrotron Self-Compton Analysis of TeV X-ray Selected BL Lacertae Objects
• Fermi Gamma-ray Imaging of a Radio Galaxy
• The X-ray nuclei of intermediate-redshift radio sources
• Chandra and XMM-Newton Observations of the Nucleus of Centaurus A
• The Hot Interstellar Medium of Normal Elliptical Galaxies. I. A Chandra Gas Gallery and Comparison of X-ray and Optical Morphology
• The Suzaku Observation of the Nucleus of the Radio-Loud Active Galaxy Centaurus A: Constraints on Abundances of the Accreting Material
• The prevalence of FRI radio quasars
• On the relationship between BL Lacertae objects and radio galaxies
• The polyhedral nature of LINERs: An XMM-Newton view of LINERs in radio galaxies

Cited by in corpus (7)

• Jet collimation in NGC 315 and other nearby AGN
• A redshifted Fe K$\alpha$ line from the unusual gamma-ray source PMN J1603-4904
• High energy emission component, population, and contribution to the extragalactic gamma-ray background of gamma-ray emitting radio galaxies
• Broadband Modeling of Low Luminosity Active Galactic Nuclei Detected in Gamma Rays
• Relationship between Gamma-ray loudness and X-ray spectra of Radio Galaxies
• Proper Motions in the sub-kiloparsec Jet of 3C 78: Novel Constraints on the Physical Nature of Relativistic Jets
• Hard X-ray view of two $\gamma$-ray detected low-luminosity active galactic nuclei: NGC 315 and NGC 4261