Fermi-LAT and Suzaku observations of the radio galaxy Centaurus B

• Published in: Astronomy and astrophysics (Berlin) 2013-02, Vol.550, p.A66
• Main Authors: Katsuta, J., Tanaka, Y. T., Stawarz, Ł., O’Sullivan, S. P., Cheung, C. C., Kataoka, J., Funk, S., Yuasa, T., Odaka, H., Takahashi, T., Svoboda, J.
• Format: Article
• Language: English
• Subjects: acceleration of particles; ASTRONOMY AND ASTROPHYSICS; galaxies: individual: Centaurus B; galaxies: jets; gamma rays: galaxies; radiation mechanisms: non-thermal; X-rays: galaxies
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361/201220270

Centaurus B is a nearby radio galaxy positioned in the southern hemisphere close to the Galactic plane. Here we present a detailed analysis of about 43 months of accumulated Fermi-LAT data of the γ-ray counterpart of the source initially reported in the 2nd Fermi-LAT catalog, and of newly acquired Suzaku X-ray data. We confirm its detection at GeV photon energies and analyze the extension and variability of the γ-ray source in the LAT dataset, in which it appears as a steady γ-ray emitter. The X-ray core of Centaurus B is detected as a bright source of a continuum radiation. We do not detect, however, any diffuse X-ray emission from the known radio lobes, with the provided upper limit only marginally consistent with the previously claimed ASCA flux. Two scenarios that connect the X-ray and γ-ray properties are considered. In the first one, we assume that the diffuse non-thermal X-ray emission component is not significantly below the derived Suzaku upper limit. In this case, modeling the inverse-Compton emission shows that the observed γ-ray flux of the source may in principle be produced within the lobes. This association would imply that efficient in-situ acceleration of the radiating electrons is occurring and that the lobes are dominated by the pressure from the relativistic particles. In the second scenario, with the diffuse X-ray emission well below the Suzaku upper limits, the lobes in the system are instead dominated by the magnetic pressure. In this case, the observed γ-ray flux is not likely to be produced within the lobes, but instead within the nuclear parts of the jet. By means of synchrotron self-Compton modeling, we show that this possibility could be consistent with the broad-band data collected for the unresolved core of Centaurus B, including the newly derived Suzaku spectrum.