Paola Pietrini

THE EFFECT OF RADIATION PRESSURE ON VIRIAL BLACK HOLE MASS ESTIMATES AND THE CASE OF NARROW-LINE SEYFERT 1 GALAXIES

We consider the effect of radiation pressure from ionizing photons on black hole (BH) mass estimates based on the application of the virial theorem to broad emission lines in AGN spectra. BH masses based only on the virial product Delta(VR)-R-2 and neglecting the effect of radiation pressure can be severely underestimated, especially in objects close to the Eddington limit. We provide an empirical calibration of the correction for radiation pressure, and we show that it is consistent with a simple physical model in which BLR clouds are optically thick to ionizing radiation and have average column densities of N-H similar to 10(23) cm(-2). This value is remarkably similar to what is required in standard BLR photoionization models to explain observed spectra. With the inclusion of radiation pressure, the discrepancy between virial BH masses based on single-epoch spectra and on reverberation mapping data drops from 0.4 to 0.2 dex rms. The use of single-epoch observations as surrogates of reverberation mapping campaigns can thus provide more accurate BH masses than previously thought. Finally, we show that narrow-line Seyfert 1 (NLS1) galaxies have apparently low BH masses because they are radiating close to their Eddington limit. After the radiation pressure correction, NLS1 galaxies have BH masses similar to other broad-line AGNs and follow the same M-BH-sigma(e)/L-sph relations as other active and normal galaxies. Radiation forces arising from ionizing photon momentum deposition constitute an important physical effect which must be taken into account when computing virial BH masses.

Comets orbiting a black hole

We use a long (300 ks), continuous Suzaku X-ray observation of the active nucleus in NGC 1365 to investigate the structure of the circumnuclear broad line region (BLR) clouds through their occultation of the X-ray source. The variations of the absorbing column density and of the covering factor indicate that the clouds surrounding the black hole are far from having a spherical geometry (as sometimes assumed), instead they have a strongly elongated and cometary shape, with a dense head (n ∼ 10 11 cm −3 ) and an expanding, dissolving tail. We infer that the cometary tails must be longer than a few times 10 13 cm and their opening angle must be smaller than a few degrees. We suggest that the cometary shape may be a common feature of BLR clouds in general, but which has been difficult to recognize observationally so far. The cometary shape may originate from shocks and hydrodynamical instabilities generated by the supersonic motion of the BLR clouds into the intracloud medium. As a consequence of the mass loss into their tail, we infer that the BLR clouds probably have a lifetime of only a few months, implying that they must be continuously replenished. We also find a large, puzzling discrepancy (two orders of magnitude) between the mass of the BLR inferred from the properties of the absorbing clouds and the mass of the BLR inferred from photoionization models; we discuss the possible solutions to this discrepancy.

X-ray absorption by broad-line region clouds in Mrk 766

We present a new analysis of a 9-d long XMM-Newton monitoring of the narrow-line Seyfert 1 galaxy Mrk 766. We show that the strong changes in the spectral shape, which occurred during this observation, can be interpreted as due to broad-line region clouds crossing the line of sight to the X-ray source. Within the occultation scenario, the spectral and temporal analyses of the eclipses provide precise estimates of the geometrical structure, location and physical properties of the absorbing clouds. In particular, we show that these clouds have cores with column densities of at least a few 10 23 cm -2 and velocities in the plane of the sky of the order of thousands of km s -1 . The three different eclipses monitored by XMM-Newton suggest a broad range in cloud velocities (by a factor of ~4-5). Moreover, two iron absorption lines clearly associated with each eclipse suggest the presence of highly ionized gas around the obscuring clouds and an outflow component of the velocity spanning from 3000 to 15 000 km s -1 .

The inverse Compton thermostat in hot plasmas near accreting black holes

The hard X-ray spectra of accreting black holes systems are generally well-fit by thermal Comptonization models with temperatures

Search for X-ray occultations in active galactic nuclei

\sim 100

Extragalactic jets as current-carrying systems. I. Equilibrium and stability

keV. We demonstrate why, over many orders of magnitude in heating rate and seed photon supply, hot plasmas radiate primarily by inverse Compton scattering, and find equilibrium temperatures within a factor of a few of 100 keV. We also determine quantitatively the (wide) bounds on heating rate and seed photon supply for which this statement is true. Plasmas in thermal balance in this regime obey two simple scaling laws, one relating the product of temperature and optical depth to the ratio of seed photon luminosity to plasma heating rate

Convective Dynamical Instability in Radiation-supported Accretion Disks

l_s/l_h

Extragalactic jets as current-carrying systems. III. Energy requirements and critical discussion

, the other relating the spectral index of the output power-law to

Stellar envelopes as sources of broad line region emission: New possibilities allowed

l_s/l_h

Magnetohydrodynamic models for extragalactic jets. II - Multistep structures

. Because