We model thermal X-ray emission from the accreting supermassive black hole Sagittarius A Ã at the Galactic center. For the region inside 1B5 of the center, we use a generalized radiatively inefficient accretion flow ( RIAF) model, and for the region out to 10 00 we use published models of the ambient hot gas. We calculate the equivalent widths of hydrogen-like and helium-like emission lines of various elements, notably iron. We predict that a strong helium-like iron line with an equivalent width $1 keV should be emitted by both the external medium and the RIAF. The equivalent width in the external medium is sensitive to the metallicity Z of the gas as well as the mean temperature. For reasonable choices of these parameters, the calculated results agree with Chandra's detection of an iron line with an equivalent width of 1.3 keV within 10 00 . The emission from within 1B5 is not sensitive to the external temperature, but is sensitive to the density and, especially, temperature profile inside the Bondi radius. For the range of profiles we consider, we calculate the equivalent width of the iron line to be $0.6-1.5(Z/Z ) keV, where Z is the solar metallicity. We present a new Chandra spectrum of the quiescent emission within 1B5 of Sgr A Ã . The measured equivalent width of the iron line is 0.7 keV. Although this measurement has a large uncertainty, it is consistent with our predictions, provided the metallicity of the gas is approximately solar.

In the frame of unification schemes for radio-loud active galactic nuclei (AGNs), FR I radio galaxies are believed to be BL Lacertae (BL Lac) objects with the relativistic jet misaligned to our line of sight, and FR II radio galaxies correspond to misaligned radio quasars. The Ledlow-Owen dividing line for the FR I/FR II dichotomy in the optical absolute magnitude of the host galaxy-radio luminosity (M R -L Rad ) plane can be translated to the line in the black hole mass-jet power (M bh -Q jet ) plane by using two empirical relations: Q jet -L Rad and M bh -M R . We use a sample of radio quasars and BL Lac objects with measured black hole masses to explore the relation of the jet power with black hole mass, in which the jet power is estimated from the extended radio emission. It is found that the BL Lac objects are clearly separated from radio quasars by the Ledlow-Owen FR I/II dividing line in the M bh -Q jet plane. This strongly supports the unification schemes for FR I/BL Lac object and FR II/radio quasar. We find that the Eddington ratios L bol /L Edd of BL Lac objects are systematically lower than those of radio quasars in the sample with a rough division at L bol /L Edd ∼ 0.01, and the distribution of Eddington ratios of BL Lac objects/quasars exhibits a bimodal nature, which imply that the accretion mode of BL Lac objects may be different from that of radio quasars.

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We study the relation of optical/UV and X-ray emission in the low luminosity active galactic nuclei (LLAGNs), using a sample of 49 sources including 28 local Seyfert galaxies and 21 low-ionization nuclear emission-line regions with optical/UV spectral luminosity at wavelength λ = 2500 Å, 23.0 log L ν(2500 Å) (erg s −1 Hz −1 ) 27.7, and X-ray spectral luminosity at 2 keV, 20.5 log L ν(2 keV) 25.3. Strong correlations are found between the X-ray luminosity and the optical/UV-to-X-ray index, α ox , with the optical/UV luminosity, with slopes very similar to the findings for the luminous AGNs in previous works. The correlation between α ox and L ν(2 keV) is very weak, as is that found for the luminous AGNs in the majority of previous similar works. We also study the relation between α ox and the Eddington ratio L bol /L Edd for our sample and find a significant anti-correlation for the sources with L bol /L Edd 10 −3 , which is opposite to the correlation between the two variables for the luminous AGNs. Using the advection-dominated accretion flow (ADAF) model, we roughly reproduce this anti-correlationship for the two variables for the LLAGNs. This result strongly supports the ADAF as a candidate for the accretion mode in LLAGNs.