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Register a new userNo Signatures of Black-Hole Spin in the X-ray Spectrum of the Seyfert 1 Galaxy Fairall 9
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Fairall 9 is one of several type 1 active galactic nuclei for which it has been claimed that the angular momentum (or spin) of the supermassive black hole can be robustly measured, using the Fe K$alpha$ emission line and Compton-reflection continuum in the X-ray spectrum. The method rests upon the interpretation of the Fe K$alpha$ line profile and associated Compton-reflection continuum in terms of relativistic broadening in the strong gravity regime in the innermost regions of an accretion disc, within a few gravitational radii of the black hole. Here, we re-examine a Suzaku X-ray spectrum of Fairall 9 and show that a face-on toroidal X-ray reprocessor model involving only nonrelativistic and mundane physics provides an excellent fit to the data. The Fe K$alpha$ line emission and Compton reflection continuum are calculated self-consistently, the iron abundance is solar, and an equatorial column density of $sim 10^{24} rm cm^{-2}$ is inferred. In this scenario, neither the Fe K$alpha$ line, nor the Compton-reflection continuum provide any information on the black-hole spin. Whereas previous analyses have assumed an infinite column density for the distant-matter reprocessor, the shape of the reflection spectrum from matter with a finite column density eliminates the need for a relativistically broadened Fe K$alpha$ line. We find a 90 per cent confidence range in the Fe K$alpha$ line FWHM of $1895$-$6205 rm km s^{-1}$, corresponding to a distance of $sim 3100$ to $33,380$ gravitational radii from the black hole, or $0.015$-$0.49$ pc for a black-hole mass of $sim 1-3 times 10^{8} M_{odot}$.
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We report on the results of spectral fits made to data obtained from a 168 ksec Suzaku observation of the Seyfert-1 galaxy Fairall 9. The source is clearly detected out to 30 keV. The observed spectrum is fairly simple; it is well-described by a power-law with a soft excess and disk reflection. A broad iron line is detected, and easily separated from distinct narrow components owing to the resolution of the CCDs in the X-ray Imaging Spectrometer (XIS). The broad line is revealed to be asymmetric, consistent with a disk origin. We fit the XIS and Hard X-ray Detector (HXD) spectra with relativistically-blurred disk reflection models. With the assumption that the inner disk extends to the innermost stable circular orbit, the best-fit model implies a black hole spin parameter of a = 0.60(7) and excludes extremal values at a high level of confidence. We discuss this result in the context of Seyfert observations and models of the cosmic distribution of black hole spin.
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.
The compact primary in the X-ray binary Cygnus X-1 was the first black hole to be established via dynamical observations. We have recently determined accurate values for its mass and distance, and for the orbital inclination angle of the binary. Building on these results, which are based on our favored (asynchronous) dynamical model, we have measured the radius of the inner edge of the black holes accretion disk by fitting its thermal continuum spectrum to a fully relativistic model of a thin accretion disk. Assuming that the spin axis of the black hole is aligned with the orbital angular momentum vector, we have determined that Cygnus X-1 contains a near-extreme Kerr black hole with a spin parameter a/M>0.95 (3sigma). For a less probable (synchronous) dynamical model, we find a/M>0.92 (3sigma). In our analysis, we include the uncertainties in black hole mass, orbital inclination angle and distance, and we also include the uncertainty in the calibration of the absolute flux via the Crab. These four sources of uncertainty totally dominate the error budget. The uncertainties introduced by the thin-disk model we employ are particularly small in this case given the extreme spin of the black hole and the disks low luminosity.
Active Galactic Nuclei (AGN) show excess X-ray emission above 10 keV compared with extrapolation of spectra from lower energies. Risaliti et al. have recently attempted to model the hard X-ray excess in the type 1.8 AGN NGC 1365, concluding that the hard excess most likely arises from Compton-scattered reflection of X-rays from an inner accretion disk close to the black hole. Their analysis disfavored a model in which the hard excess arises from a high column density of circumnuclear gas partially covering a primary X-ray source, despite such components being required in the NGC 1365 data below 10 keV. Using a Monte Carlo radiative transfer approach, we demonstrate that this conclusion is invalidated by (i) use of slab absorption models, which have unrealistic transmission spectra for partial covering gas, (ii) neglect of the effect of Compton scattering on transmitted spectra and (iii) inadequate modeling of the spectrum of scattered X-rays. The scattered spectrum is geometry dependent and, for high global covering factors, may dominate above 10 keV. We further show that, in models of circumnuclear gas, the suppression of the observed hard X-ray flux by reprocessing may be no larger than required by the `light bending model invoked for inner disk reflection, and the expected emission line strengths lie within the observed range. We conclude that the time-invariant `red wing in AGN X-ray spectra is probably caused by continuum transmitted through and scattered from circumnuclear gas, not by highly redshifted line emission, and that measurement of black hole spin is not possible.
Narrow-line Seyfert 1 galaxies have been identified by the Fermi Gamma-Ray Space Telescope as a rare class of gamma-ray emitting active galactic nuclei (AGN). The lowest-redshift candidate among them is the source 1H 0323+342. Here we present quasi-simultaneous Gemini near-infrared and Keck optical spectroscopy for it, from which we derive a black hole mass based on both the broad Balmer and Paschen emission lines. We supplement these observations with a NuSTAR X-ray spectrum taken about two years earlier, from which we constrain the black hole mass based on the short timescale spectral variability. Our multiwavelength observations suggest a black hole mass of ~2x10^7 solar masses, which agrees well with previous estimates. We build the spectral energy distribution and show that it is dominated by the thermal and reprocessed emission from the accretion disc rather than the non-thermal jet component. A detailed spectral fitting with the energy-conserving accretion disc model of Done et al. constrains the Eddington ratio to L/L_Edd ~ 0.5 for a (non-rotating) Schwarzschild black hole and to L/L_Edd ~ 1 for a Kerr black hole with dimensionless spin of a*=0.8. Higher spin values and so higher Eddington ratios are excluded, since they would strongly overpredict the observed soft X-ray flux.
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