67 research outputs found
Hosts of Type II Quasars: an HST Study
Type II quasars are luminous Active Galactic Nuclei whose centers are
obscured by large amounts of gas and dust. In this contribution we present
3-band HST images of nine type II quasars with redshifts 0.25<z<0.4 selected
from the Sloan Digital Sky Survey based on their emission line properties. The
intrinsic luminosities of these quasars are thought to be in the range
-24>M_B>-26, but optical obscuration implies that host galaxies can be studied
unencumbered by bright nuclei. Each object has been imaged in three filters
(`red', `green' and `blue') placed between the strong emission lines. The
spectacular, high quality images reveal a wealth of details about the structure
of the host galaxies and their environments. Most galaxies in the sample are
ellipticals, but strong deviations from de Vaucouleurs profiles are found,
especially in the blue band. We argue that most of these deviations are due to
the light from the nucleus scattered off interstellar material in the host
galaxy. This scattered component can make a significant contribution to the
broad-band flux and complicates the analysis of the colors of the stellar
populations in the host galaxy. This extended component can be difficult to
notice in unobscured luminous quasars and may bias the results of host galaxy
studies.Comment: 6 pages including 2 color figures; proceedings of the 'QSO host
galaxies: evolution and environment' conference, Leiden, August 200
Rms-flux relation in the optical fast variability data of BL Lacertae object S5 0716+714
The possibility that BL Lac S5 0716+714 exhibits a linear root mean square
(rms)-flux relation in its IntraDay Variability (IDV) is analysed. The results
may be used as an argument in the existing debate regarding the source of
optical IDV in Active Galactic Nuclei. 63 time series in different optical
bands were used. A linear rms-flux relation at a confidence level higher than
65% was recovered for less than 8% of the cases. We were able to check if the
magnitude is log-normally distributed for eight timeseries and found, with a
confidence > 95%, that this is not the case.Comment: Accepted by Astrophysics and Space Scienc
Modeling of Photoionized Plasmas
In this paper I review the motivation and current status of modeling of
plasmas exposed to strong radiation fields, as it applies to the study of
cosmic X-ray sources. This includes some of the astrophysical issues which can
be addressed, the ingredients for the models, the current computational tools,
the limitations imposed by currently available atomic data, and the validity of
some of the standard assumptions. I will also discuss ideas for the future:
challenges associated with future missions, opportunities presented by improved
computers, and goals for atomic data collection.Comment: 17 pages, 8 figures, to appear in the proceedings of Xray2010,
Utrecht, the Netherlands, March 15-17 201
Gravitationally lensed QSOs in the ISSIS/WSO-UV era
Gravitationally lensed QSOs (GLQs) at redshift z = 1-2 play a key role in
understanding the cosmic evolution of the innermost parts of active galaxies
(black holes, accretion disks, coronas and internal jets), as well as the
structure of galaxies at intermediate redshifts. With respect to studies of
normal QSOs, GLQ programmes have several advantages. For example, a monitoring
of GLQs may lead to unambiguous detections of intrinsic and extrinsic
variations. Both kinds of variations can be used to discuss central engines in
distant QSOs, and mass distributions and compositions of lensing galaxies. In
this context, UV data are of particular interest, since they correspond to
emissions from the immediate surroundings of the supermassive black hole. We
describe some observation strategies to analyse optically bright GLQs at z of
about 1.5, using ISSIS (CfS) on board World Space Observatory-Ultraviolet.Comment: 7 pages, 4 figures, Accepted for publication in Astrophysics & Space
Scienc
Atomic X-ray Spectroscopy of Accreting Black Holes
Current astrophysical research suggests that the most persistently luminous
objects in the Universe are powered by the flow of matter through accretion
disks onto black holes. Accretion disk systems are observed to emit copious
radiation across the electromagnetic spectrum, each energy band providing
access to rather distinct regimes of physical conditions and geometric scale.
X-ray emission probes the innermost regions of the accretion disk, where
relativistic effects prevail. While this has been known for decades, it also
has been acknowledged that inferring physical conditions in the relativistic
regime from the behavior of the X-ray continuum is problematic and not
satisfactorily constraining. With the discovery in the 1990s of iron X-ray
lines bearing signatures of relativistic distortion came the hope that such
emission would more firmly constrain models of disk accretion near black holes,
as well as provide observational criteria by which to test general relativity
in the strong field limit. Here we provide an introduction to this phenomenon.
While the presentation is intended to be primarily tutorial in nature, we aim
also to acquaint the reader with trends in current research. To achieve these
ends, we present the basic applications of general relativity that pertain to
X-ray spectroscopic observations of black hole accretion disk systems, focusing
on the Schwarzschild and Kerr solutions to the Einstein field equations. To
this we add treatments of the fundamental concepts associated with the
theoretical and modeling aspects of accretion disks, as well as relevant topics
from observational and theoretical X-ray spectroscopy.Comment: 63 pages, 21 figures, Einstein Centennial Review Article, Canadian
Journal of Physics, in pres
Orbital resonances in discs around braneworld Kerr black holes
Rotating black holes in the brany universe of the Randall-Sundrum type are
described by the Kerr geometry with a tidal charge b representing the
interaction of the brany black hole and the bulk spacetime. For b<0 rotating
black holes with dimensionless spin a>1 are allowed. We investigate the role of
the tidal charge b in the orbital resonance model of QPOs in black hole
systems. The orbital Keplerian, the radial and vertical epicyclic frequencies
of the equatorial, quasicircular geodetical motion are given and their radial
profiles are discussed. The resonant conditions are given in three
astrophysically relevant situations: for direct (parametric) resonances, for
the relativistic precession model, and for some trapped oscillations of the
warped discs, with resonant combinational frequencies. It is shown, how b could
influence matching of the observational data indicating the 3:2 frequency ratio
observed in GRS 1915+105 microquasar with prediction of the orbital resonance
model; limits on allowed range of the black hole parameters a and b are
established. The "magic" dimensionless black hole spin enabling presence of
strong resonant phenomena at the radius where \nu_K:\nu_{\theta}:\nu_r=3:2:1 is
determined in dependence on b. Such strong resonances could be relevant even in
sources with highly scattered resonant frequencies, as those expected in Sgr
A*. The specific values of a and b are given also for existence of specific
radius where \nu_K:\nu_{\theta}:\nu_r=s:t:u with 5>=s>t>u being small natural
numbers. It is shown that for some ratios such situation is impossible in the
field of black holes. We can conclude that analysing the microquasars
high-frequency QPOs in the framework of orbital resonance models, we can put
relevant limits on the tidal charge of brany Kerr black holes.Comment: 31 pages, 19 figures, to appear in General Relativity and Gravitatio
Matter Outflows from AGN: A Unifying Model
We discuss a self-consistent unified model of the matter outflows from AGNs
based on a theoretical approach and involving data on AGN evolution and
structure. The model includes a unified geometry, two-phase gas dynamics,
radiation transfer, and absorption spectrum calculations in the UV and X-ray
bands. We briefly discuss several questions about the mass sources of the
flows, the covering factors, and the stability of the narrow absorption
details.Comment: 6 figures, accepted for publication in Astrophysics and Space Scienc
Toy model for a two-dimensional accretion disk dominated by Poynting flux
We discuss the effect of the Poynting flow on the magnetically dominated thin
accretion disk, which is simplified to a two-dimensional disk on the equatorial
plane. It is shown in the relativistic formulation that the Poynting flux by
the rotating magnetic field with Keplerian angular velocity can balance the
energy and angular momentum conservation of a steady accretion flow.Comment: 17 pages, no figure
Quasars and their host galaxies
This review attempts to describe developments in the fields of quasar and
quasar host galaxies in the past five. In this time period, the Sloan and 2dF
quasar surveys have added several tens of thousands of quasars, with Sloan
quasars being found to z>6. Obscured, or partially obscured quasars have begun
to be found in significant numbers. Black hole mass estimates for quasars, and
our confidence in them, have improved significantly, allowing a start on
relating quasar properties such as radio jet power to fundamental parameters of
the quasar such as black hole mass and accretion rate. Quasar host galaxy
studies have allowed us to find and characterize the host galaxies of quasars
to z>2. Despite these developments, many questions remain unresolved, in
particular the origin of the close relationship between black hole mass and
galaxy bulge mass/velocity dispersion seen in local galaxies.Comment: Review article, to appear in Astrophysics Update
QCD Corrections to QED Vacuum Polarization
We compute QCD corrections to QED calculations for vacuum polarization in
background magnetic fields. Formally, the diagram for virtual loops
is identical to the one for virtual loops. However due to
confinement, or to the growth of as decreases, a direct
calculation of the diagram is not allowed. At large we consider the
virtual diagram, in the intermediate region we discuss the role of
the contribution of quark condensates \left and at the
low-energy limit we consider the , as well as charged pion
loops. Although these effects seem to be out of the measurement accuracy of
photon-photon laboratory experiments they may be relevant for -ray
burst propagation. In particular, for emissions from the center of the galaxy
(8.5 kpc), we show that the mixing between the neutral pseudo-scalar pion
and photons renders a deviation from the power-law spectrum in the
range. As for scalar quark condensates \left and
virtual loops are relevant only for very high radiation density
and very strong magnetic fields of order .Comment: 15 pages, 4 figures; Final versio
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