Suzaku X-ray measurements of time variability of broard-band X-ray spectrum of a radio galaxy Cen A
Abstract
Recent GeV and TeV gamma-ray observations have revealed that misaligned-jet radio galaxies are also gamma-ray emittors, such as NGC 1275, M87, and Cen A. Their SED is similar to that of typical blazars; synchrotron emission and inverse Compton scattering. In fact, a hard X-ray tail is observed for NGC 1275 and M87. For the Cen A, the X-ray spectrum is known to be very similar to that of Seyfert galaxies; X-ray emission is dominated by the disk emission. However, gamma-ray detection of Cen A predicts that the jet emission significantly contributes to the X-ray band. So far, X-ray studies of time-averaged spectra of radio galaxies cannot have separated the disk and jet emission. On the other hand, Suzaku for the first time revealed that the jet emission is significant in the X-ray band for a radio galaxy 3C120 (Kataoka et al. 2007), based on the study of time variation of X-ray spectrum. Therefore, studies of time variability in the broard X-ray band is a strong tool to decompose the spectral components. Such an approach is in fact utilized to decompose the direct and reflection component of Seyfert galaxies. Here, we report the Suzaku long-look observation of Cen A on 2009 summar. Cen A was time-variable in the Suzaku band with a time scale of sub-days by a factor of several tens percents. Suzaku for the first time measured the short-term time variability of Cen A above 100 keV, thanks to the high signal-to-noise ratio of Suzaku HXD. The spectrum is represented by an absorbed power-law component and a strong Fe-K line. The absorption is likely due to the dust lane. The equivalent width of Fe-K line is around 30 eV, indicating that the Fe-K line cannot be explained by only the absorber toward a line of sight. The center energy is consistent with a neutral iron line, indicating that the Fe-K emittor is far away from the nucleus. These indicate that the X-ray emission is not beamed but dominated by an isotropic disk emission at least around 10 keV. The flux well correlates between 10-40 keV and 100-200 keV, indicating that the emission component is the same between 10-40 keV and 100-200 keV; the disk emission is dominant below 200 keV. We discuss an upper limit of the jet emission around 100-200 keV.
- Publication:
-
38th COSPAR Scientific Assembly
- Pub Date:
- 2010
- Bibcode:
- 2010cosp...38.2248F