875 research outputs found
Active galaxy unification in the era of X-ray polarimetry
Active Galactic Nuclei (AGN), Seyfert galaxies and quasars, are powered by
luminous accretion and often accompanied by winds which are powerful enough to
affect the AGN mass budget, and whose observational appearance bears an imprint
of processes which are happening within the central parsec around the black
hole (BH). One example of such a wind is the partially ionized gas responsible
for X-ray and UV absorption ('warm absorbers'). Here we show that such gas will
have a distinct signature when viewed in polarized X-rays. Observations of such
polarization can test models for the geometry of the flow, and the gas
responsible for launching and collimating it. We present calculations which
show that the polarization depends on the hydrodynamics of the flow, the
quantum mechanics of resonance line scattering and the transfer of polarized
X-ray light in the highly ionized moving gas. The results emphasize the three
dimensional nature of the wind for modeling spectra. We show that the
polarization in the 0.1-10 keV energy range is dominated by the effects of
resonance lines. We predict a X-ray polarization signature of type-2
objects in this energy range. These results are general to flows which
originate from a cold torus-like structure, located pc from the BH,
which wraps the BH and is ultimately responsible for the apparent dichotomy
between type 1 and type 2 AGNs. Such signals will be detectable by future
dedicated X-ray polarimetry space missions, such as the NASA Gravity and
Extreme Magnetism SMEX, GEMS.Comment: 13 pages, 4 figures, ApJ Letters accepted for publicatio
Consequences of hot gas in the broad line region of active galactic nuclei
Models for hot gas in the broad line region of active galactic nuclei are discussed. The results of the two phase equilibrium models for confinement of broad line clouds by Compton heated gas are used to show that high luminosity quasars are expected to show Fe XXVI L alpha line absorption which will be observed with spectrometers such as those planned for the future X-ray spectroscopy experiments. Two phase equilibrium models also predict that the gas in the broad line clouds and the confining medium may be Compton thick. It is shown that the combined effects of Comptonization and photoabsorption can suppress both the broad emission lines and X-rays in the Einstein and HEAO-1 energy bands. The observed properties of such Compton thick active galaxies are expected to be similar to those of Seyfert 2 nuclei. The implications for polarization and variability are also discussed
AGN Torus Threaded by Large Scale Magnetic Field
Large scale magnetic eld can be easily dragged from galactic scales towards AGN alongwith accreting gas. There, it can contribute to both the formation of AGN "torus" and help to remove angular momentum from the gas which fuels AGN accretion disk. Howeverthe dynamics of such gas is also strongly inuenced by the radiative feedback from theinner accretion disk. Here we present results from the three-dimensional simulations ofpc-scale accretion which is exposed to intense X-ray heating
An axisymmetric, hydrodynamical model for the torus wind in AGN
We report on time-dependent axisymmetric simulations of an X-ray excited flow
from a parsec-scale, rotating, cold torus around an active galactic nucleus.
Our simulations account for radiative heating and cooling and radiation
pressure force. The simulations follow the development of a broad bi-conical
outflow induced mainly by X-ray heating. We compute synthetic spectra predicted
by our simulations. The wind characteristics and the spectra support the
hypothesis that a rotationally supported torus can serve as the source of a
wind which is responsible for the warm absorber gas observed in the X-ray
spectra of many Seyfert galaxies.Comment: ApJ Letters, accepted for publicatio
An axisymmetric hydrodynamical model for the torus wind in AGN. III: Spectra from 3D radiation transfer calculations
We calculate a series of synthetic X-ray spectra from outflows originating
from the obscuring torus in active galactic nuclei (AGN). Such modeling
includes 2.5D hydrodynamical simulations of an X-ray excited torus wind,
including the effects of X-ray heating, ionization, and radiation pressure. 3D
radiation transfer calculations are performed in the 3D Sobolev approximation.
Synthetic X-ray line spectra and individual profiles of several strong lines
are shown at different inclination angles, observing times, and for different
characteristics of the torus.
Our calculations show that rich synthetic warm absorber spectra from 3D
modeling are typically observed at a larger range of inclinations than was
previously inferred from simple analysis of the transmitted spectra. In
general, our results are supportive of warm absorber models based on the
hypothesis of an "X-ray excited funnel flow" and are consistent with
characteristics of such flows inferred from observations of warm absorbers from
Seyfert 1 galaxies.Comment: 31 pages, 10 figure
Time-dependent Photoionization of Gaseous Nebulae: the Pure Hydrogen Case
We study the problem of time-dependent photoionization of low density gaseous
nebulae subjected to sudden changes in the intensity of ionizing radiation. To
this end, we write a computer code that solves the full time-dependent energy
balance, ionization balance, and radiation transfer equations in a
self-consistent fashion for a simplified pure hydrogen case. It is shown that
changes in the ionizing radiation yield ionization/thermal fronts that
propagate through the cloud, but the propagation times and response times to
such fronts vary widely and non-linearly from the illuminated face of the cloud
to the ionization front (IF). Ionization/thermal fronts are often supersonic,
and in slabs initially in pressure equilibrium such fronts yield large pressure
imbalances that are likely to produce important dynamical effects in the cloud.
Further, we studied the case of periodic variations in the ionizing flux. It
is found that the physical conditions of the plasma have complex behaviors that
differ from any steady-state solutions. Moreover, even the time average
ionization and temperature is different from any steady-state case. This time
average is characterized by over-ionization and a broader IF with respect to
the steady-state solution for a mean value of the radiation flux. Around the
time average of physical conditions there is large dispersion in instantaneous
conditions, particularly across the IF, which increases with the period of
radiation flux variations. Moreover, the variations in physical conditions are
asynchronous along the slab due to the combination of non-linear propagation
times for thermal/ionization fronts and equilibration times.Comment: Accepted for publication in ApJ. 36 pages, 12 figure
- …