Scaling of X-ray spectral properties of a black hole in the Seyfert 1
  galaxy NGC~7469
  We present our analysis of X-ray spectral properties observed from the
Seyfrert 1 galactic nucleus NGC~7469 using the RXTE and ASCA observations. We
demonstrate strong observational evidence that NGC~7469 undergoes spectral
transitions from the low hard state (LHS) to the intermediate state (IS) during
these observations. The RXTE observations (1996--2009) show that the source was
in the IS ~ 75 % of the time only, ~ 25 % of the time in the LHS. The spectra
of NGC~7469 are well fitted by the so-called bulk motion Comptonization (BMC)
model for all spectral states. We have established the photon index saturation
level, Gamma_{sat}+2.1+/-0.1, in the Gamma versus mass accretion rate, Mdot
correlation. This Gamma- Mdot correlation allows us to estimate the black hole
(BH) mass in NGC~7469 to be M__BH> 3 x 10^6 solar masses assuming the distance
to NGC~7469 of 70 Mpc. For this BH mass estimate, we use the scaling method
taking Galactic BHs, GRO~J1655--40, Cyg~ X--1 and an extragalactic BH source,
NGC~4051 as reference sources. The Gamma versus Mdot correlation revealed in
NGC~7469 is similar to those in a number of Galactic and extragalactic BHs and
it clearly shows the correlation along with the strong Gamma saturation at
~2.1. This is robust observational evidence for the presence of a BH in
NGC~7469. We also find that the seed photon temperatures are quite low, of the
order of 140-200 eV, which are consistent with a high BH mass in NGC~7469 that
is more than 3x10^6 solar masses.
