Abstract

Fermi-LAT has detected about ten radio galaxies in the GeV band. Since the origin of X-ray emission of these FR-I radio galaxies is still not understood, particularly whether the jet component exists or not, we analyzed or observed these GeV emitting FR-I radio galaxies with the Suzaku X-ray satellite. Cen A, the brightest in the hard X-ray band, was in an active phase in 2009. The spectrum became harder by a photon index difference of $sim$0.2 than those in the 2005 low state. Analyzing time variation of X-ray spectra, an additional hard powerlaw component with a photon index of 1.2 in 2009 is suggested. This hard component is implied to be a lower part of the inverse Compoton scattering component from the jet.

We also analyzed the Suzaku data of NGC1275, which has been observed every 6 months for calibration. The emission of NGC 1275 nucleus is detected against the cluster emission, but the X-ray flux is almost constant over 6 years, while the GeV gamma-ray and radio emission showed variability. We also observed NGC1275 with the KANATA optical telescope and found no variability and an upper limit of polarization is 1.5%. Therefore, the X-ray emission is considered to come from the disk or the jet whose emission region is different from that of GeV gamma-rays. We also present the analysis of Suzaku data of other FR-I radio galaxies, and discuss the systematic X-ray and SED properties.