Kiyoshi Hayashida et al. 1998 ApJ 500 642 doi:10.1086/305736
Kiyoshi Hayashida1,3, Sigenori Miyamoto1,4, Shunji Kitamoto1,3, Hitoshi Negoro1,5 and Hajime Inoue2
Show affiliationsCentral black hole masses in eight active galactic nuclei (AGNs) are evaluated by a method based on the X-ray flux variability of these AGNs and Cyg X-1 observed with Ginga. We introduce a new definition for the variability timescale by employing a normalized power spectral density function. Assuming a linear proportionality between the variability timescale and the mass of the central black hole, and using the relation between these two for Cyg X-1 as a reference point, we estimate the masses of eight AGNs (six Seyferts, one quasar, and one BL Lacertae type object). The masses evaluated in this way are lower than those in earlier estimates (or upper limits) using different methods by a factor of 1 or 2 orders of magnitude, for some sources. We thus obtain a logarithmically averaged Eddington ratio of 1.4 for eight sources, or 0.47 for six Seyferts excluding a quasar and a BL Lacertae-type object. We discuss significance of this high Eddington ratio for the emission mechanism and the cosmological evolution of AGNs.
black hole physics; galaxies: active; galaxies: nuclei; X-rays: galaxies
Issue 2 (1998 June 20)
Received 1994 October 27, accepted for publication 1998 January 1
Kiyoshi Hayashida et al. 1998 ApJ 500 642