1,328 research outputs found
Eddington Accretion and QSO Emission Lines at z ~ 2
Broad Absorption Line (BAL) QSOs have been suggested to be youthful
super-accretors based on their powerful radiatively driven absorbing outflows
and often reddened continua. To test this hypothesis, we observed near IR
spectra of the H region for 11 bright BAL QSOs at redshift z ~ 2. We
measured these and literature spectra for 6 BAL QSOs, 13 radio-loud and 7
radio-quiet non-BAL QSOs. Using the luminosity and H broad line width to
derive black hole mass and accretion rate, we find that both BAL and non-BAL
QSOs at z ~ 2 tend to have higher than those at low z -- probably a
result of selecting the brightest QSOs. However, we find that the high z QSOs,
in particular the BAL QSOs, have extremely strong Fe II and very weak [O III],
extending the inverse relationship found for low z QSOs. This suggests that,
even while radiating near , the BAL QSOs have a more plentiful fuel
supply than non-BAL QSOs. Comparison with low z QSOs shows for the first time
that the inverse Fe II -- [O III] relationship is indeed related to
, rather than black hole mass.Comment: 18 pages including 5 figures and 1 table. Accepted by the
Astrophysical Journal Letter
On why the Iron K-shell absorption in AGN is not a signature of the local Warm/Hot Intergalactic Medium
We present a comparison between the 2001 XMM-Newton and 2005 Suzaku
observations of the quasar, PG1211+143 at z=0.0809. Variability is observed in
the 7 keV iron K-shell absorption line (at 7.6 keV in the quasar frame), which
is significantly weaker in 2005 than during the 2001 XMM-Newton observation.
From a recombination timescale of <4 years, this implies an absorber density
n>0.004 particles/cm3, while the absorber column is 5e22<N_H <1 1e24
particles/cm2. Thus the sizescale of the absorber is too compact (pc scale) and
the surface brightness of the dense gas too high (by 9-10 orders of magnitude)
to arise from local hot gas, such as the local bubble, group or Warm/Hot
Intergalactic Medium (WHIM), as suggested by McKernan et al. (2004, 2005).
Instead the iron K-shell absorption must be associated with an AGN outflow with
mildly relativistic velocities. Finally we show that the the association of the
absorption in PG1211+143 with local hot gas is simply a coincidence, the
comparison between the recession and iron K absorber outflow velocities in
other AGN does not reveal a one to one kinematic correlation.Comment: accepted for publication in MNRAS LETTERS. 5 pages, 4 figure
Soft X-ray spectral variations of the narrow line Seyfert l galaxy Markarian 766
The X-ray variability of the narrow-line Seyfert 1 galaxy Markarian 766 is studied using nine ROSAT PSPC data sets. The spectrum is well described by a power law combined with a blackbody (kT ∼ 70 eV) soft excess. Examination of flux ratio changes and variability amplitude in three X-ray bands shows that the power-law component varies continuously on time-scales of ∼ 5000 s and is steeper when it is brighter. In contrast, variability of the soft excess is not detected. Spectral modelling of 31 spectra from different observations and at a range of count rates is also consistent with a picture in which the power law is steeper when it is brighter, and in which the soft-excess component does not vary. The power-law variability can be explained if the power law is produced by variable thermal or non-thermal Comptonization of soft photons. This behaviour is similar to that of Galactic black hole candidates in the low state. The X-ray and multiwavelength properties of Markarian 766 are shown to be very similar to those of other narrow-line Seyfert 1s. This may mean that the rapid X-ray variability seen in other narrow-line Seyfert 1s may also not originate in their strong soft-excess components
Geometry and Kinematics in the Central Broad-Line Region of a Seyfert 1 Galaxy
We recorded spectra of the highly variable Seyfert 1 galaxy Mrk110 in a
variability campaign with the 9.2m Hobby-Eberly Telescope at McDonald
Observatory in order to study the detailed line profile variations of the broad
emission lines. Here we show that only an AGN model predicting the formation of
the broad Hb line emission in the wind of an accretion disk matches the
observed 2-D variability pattern. Furthermore, we derive an improved mass of
the central supermassive black hole of M = 1.0(+1.0,-0.5)E7 M_sun from the Hb
velocity-delay map.Comment: 4 pages, 10 figures. A&A Letters, in pres
Let Me Introduce You to a New PEER: The Postsecondary Education, Employment, and Research Project at USU
High resolution study of associated C IV absorption systems in NGC 5548
We present the results of a careful analysis of associated absorption systems
toward NGC 5548. Most of the well resolved narrow components in the associated
system, defined by the Lyman alpha, C IV and N V profiles, show velocity
separation similar (to within 10~\kms) to the C IV doublet splitting. We
estimate the chance probability of occurrence of such pairs with velocity
separation equal to C IV doublet splitting to be . Thus it is
more likely that most of the narrow components are line-locked with C IV
doublet splitting. This will mean that the radiative acceleration plays an
important role in the kinematics of the absorbing clouds. We build grids of
photoionization models and estimate the radiative acceleration due to all
possible bound-bound transitions. We show that the clouds producing absorption
have densities less than , and are in the outer regions of the
broad emission line region (BLR). We note that the clouds which are line-locked
cannot produce appreciable optical depths of O VII and O VIII, and hence cannot
be responsible for the observed ionized edges, in the soft X-ray. We discuss
the implications of the presence of optically thin clouds in the outer regions
of the BLR to the models of broad emission lines.Comment: 21 pages, latex (aasms4 style), incluedes 4 ps figures. To appear in
Astrophysical Journa
A burst from the direction of UZ Fornacis with XMM-Newton
The XMM-Newton pointing towards the magnetic cataclysmic variable UZ For
finds the source to be a factor > 10^3 fainter than previous EXOSAT and ROSAT
observations. The source was not detected for the majority of a 22 ksec
exposure with the EPIC cameras, suggesting that the accretion rate either
decreased, or stopped altogether. However a 1.1 ksec burst was detected from UZ
For during the observation. Spectral fits favour optically thin, kT = 4.4 keV
thermal emission. Detection of the burst by the on-board Optical Monitor
indicates that this was most probably an accretion event. The 0.1-10 keV
luminosity of 2.1 x 10^30 erg/s is typical for accretion shock emission from
high state polars and would result from the potential energy release of ~ 10^16
g of gas. There is no significant soft excess due to reprocessing in the white
dwarf atmosphere.Comment: 7 pages, 2 postscript figures, ApJL, in pres
X-ray spectroscopy and photometry of the long-period polar AI Tri with XMM-Newton
Context. The energy balance of cataclysmic variables with strong magnetic
fields is a central subject in understanding accretion processes on magnetic
white dwarfs. With XMM-Newton, we perform a spectroscopic and photometric study
of soft X-ray selected polars during their high states of accretion. Aims. On
the basis of X-ray and optical observations of the magnetic cataclysmic
variable AI Tri, we derive the properties of the spectral components, their
flux contributions, and the physical structure of the accretion region in soft
polars. Methods. We use multi-temperature approaches in our xspec modeling of
the spectra to describe the physical conditions and the structures of the
post-shock accretion flow and the accretion spot on the white-dwarf surface. In
addition, we investigate the accretion geometry of the system by a timing
analysis of the photometric data. Results. Flaring soft X-ray emission from the
heated surface of the white dwarf dominates the X-ray flux during roughly 70%
of the binary cycle. This component deviates from a single black body and can
be described by a superimposition of mildly absorbed black bodies with a
Gaussian temperature distribution. In addition, weaker hard X-ray emission is
visible nearly all the time. The spectrum from the cooling post-shock accretion
flow is most closely fitted by a combination of thermal plasma mekal models
with temperature profiles adapted from prior stationary two-fluid hydrodynamic
calculations. The soft X-ray light curves show a dip during the bright phase,
which can be interpreted as self-absorption in the accretion stream.
Phase-resolved spectral modeling supports the picture of one-pole accretion and
self-eclipse. One of the optical light curves corresponds to an irregular mode
of accretion. During a short XMM-Newton observation at the same epoch, the
X-ray emission of the system is clearly dominated by the soft component.Comment: A&A, in press; 11 pages, 9 figures, 3 table
Cyclotron modeling phase-resolved infrared spectroscopy of polars I: EF Eridani
We present phase-resolved low resolution infrared spectra of the polar EF
Eridani obtained over a period of 2 years with SPEX on the IRTF. The spectra,
covering the wavelength range 0.8 to 2.4 microns, are dominated by cyclotron
emission at all phases. We use a ``Constant Lambda'' prescription to attempt to
model the changing cyclotron features seen in the spectra. A single cyclotron
emission component with B = 12.6 MG, and a plasma temperature of kT = 5.0 keV,
does a reasonable job in matching the features seen in the H and K bands, but
fails to completely reproduce the morphology shortward of 1.6 microns. We find
that a two component model, where both components have similar properties, but
whose contributions differ with viewing geometry, provides an excellent fit to
the data. We discuss the implications of our models and compare them with
previously published results. In addition, we show that a cyclotron model with
similar properties to those used for modeling the infrared spectra, but with a
field strength of B = 115 MG, can explain the GALEX observations of EF Eri.Comment: 25 pages, 5 figures, to appear in Ap
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