Scaling of X-ray spectral properties of a black hole in the Seyfert 1 galaxy NGC7469

We present our analysis of X-ray spectral properties observed from the Seyfert 1 galactic nucleus NGC 7469 using the Rossi X-ray Timing Explorer (RXTE) and Advanced Satellite for Cosmology and Astrophysics mission (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 (Γ) saturation level, Γsat = 2.1 ± 0.1, in the Γ versus mass accretion rate, Ṁ correlation. This Γ – Ṁ correlation allows us to estimate the black hole (BH) mass in NGC 7469 to be MBH ≥ 3 × 106 M⊙ 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 Γ versus Ṁ 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 Γ saturation at ≈2.1. This is robust observational evidence for the presence of a BH in NGC 7469. We also find that the seed (disk) 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 3 × 106 solar masses.

AGN black hole mass estimates using polarization in broad emission lines

Context. The innermost regions in active galactic nuclei (AGNs) have not yet been spatially resolved, but spectropolarimetry can provide insight into their hidden physics and geometry. From spectropolarimetric observations in broad emission lines and assuming equatorial scattering as a dominant polarization mechanism, it is possible to estimate the mass of supermassive black holes (SMBHs) residing at the center of AGNs. Aims. We explore the possibilities and limits, and put constraints on the method for determining SMBH masses using polarization in broad emission lines by providing more in-depth theoretical modeling. Methods. We used the Monte Carlo radiative transfer code STOKES to explore polarization properties of Type-1 AGNs. We modeled equatorial scattering using flared-disk geometry for a set of different SMBH masses assuming Thomson scattering. In addition to the Keplerian motion, which is assumed to be dominant in the broad-line region (BLR), we also considered cases of additional radial inflows and vertical outflows. Results. We modeled the profiles of polarization plane position angle φ, degree of polarization, and total unpolarized lines for different BLR geometries and different SMBH masses. Our model confirms that the method can be widely used for Type-1 AGNs when viewing inclinations are between 25° and 45°. We show that the distance between the BLR and scattering region (SR) has a significant impact on the mass estimates and the best mass estimates are when the SR is situated at a distance 1.5–2.5 times larger than the outer BLR radius. Conclusions. Our models show that if Keplerian motion can be traced through the polarized line profile, then the direct estimation of the mass of the SMBH can be performed. When radial inflows or vertical outflows are present in the BLR, this method can still be applied if velocities of the inflow/outflow are less than 500 km s−1. We also find that models for NGC 4051, NGC 4151, 3C 273, and PG0844+349 are in good agreement with observations.

NGC 4051: Black hole mass and photon index-mass accretion rate correlation

We present a discovery of the correlation between the X-ray spectral (photon) index and mass accretion rate observed in an active galactic nucleus, NGC 4051. We analyzed spectral transition episodes observed in NGC 4051 using XMM-Newton, Suzaku and RXTE. We applied a scaling technique for a black hole (BH) mass evaluation which uses a correlation between the photon index and normalization of the seed (disk) component, which is proportional to a mass accretion rate. We developed an analytical model that shows the spectral (photon) index of the BH emergent spectrum undergoes an evolution from lower to higher values depending on a mass accretion rate in the accretion disk. We considered Cygnus X-1 and GRO J1550–564 as reference sources for which distances, inclination angles and the BH masses are evaluated by dynamical measurements. Application of the scaling technique for the photon index−mass accretion rate correlation provides an estimate of the black hole mass in NGC 4051 to be more than 6 × 105 solar masses.