Journal
ASTROPHYSICAL JOURNAL
Volume 798, Issue 2, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/798/2/74
Keywords
galaxies: jets; gamma rays: galaxies; X-rays: galaxies
Categories
Funding
- JSPS KAKENHI [2400000401, 2424401400]
- Polish NSC [DEC-2012/04/A/ST9/00083]
- National Aeronautics and Space Administration
- Department of Energy in the United States
- Commissariat a l'Energie Atomique
- Centre National de la Recherche Scientifique/Institut National de Physique Nucleaire et de Physique des Particules in France
- Agenzia Spaziale Italiana
- Istituto Nazionale di Fisica Nucleare in Italy
- Ministry of Education, Culture, Sports, Science and Technology (MEXT)
- High Energy Accelerator Research Organization (KEK)
- Japan Aerospace Exploration Agency (JAXA) in Japan
- K. A. Wallenberg Foundation
- Swedish Research Council
- Swedish National Space Board in Sweden
- Istituto Nazionale di Astrofisica in Italy
- Centre National d'Etudes Spatiales in France
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We performed a systematic X-ray study of eight nearby gamma-ray bright radio galaxies with Suzaku in order to understand the origins of their X-ray emissions. The Suzaku spectra for five of those have been presented previously, while the remaining three (M87, PKS 0625-354, and 3C 78) 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 PKS 0625-354 and 3C 78 to understand these sources within the blazar paradigm. We found significant gamma-ray variability in the former object. Overall, we note that the Suzaku spectra for both PKS 0625-354 and 3C 78 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 broadband spectral energy distributions of PKS 0625-354 and 3C 78 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 Lacertae (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 (similar to 10(16) Hz) synchrotron frequencies in the two analyzed sources, contrary to previously suggested scenarios for Fanaroff-Riley (FR) type I/BL Lac unification. We discuss the implications of our findings in the context of the FR I/BL Lac unification schemes.
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