2,392 research outputs found
Exploratory ASCA Observations of Broad Absorption Line Quasi-Stellar Objects
We present the analysis and interpretation of a sample of eight ASCA
observations of Broad Absorption Line Quasi-Stellar Objects (BALQSOs). This is
the first moderate-sized sample of sensitive BALQSO observations above 2 keV,
and the BALQSOs in our sample are among the optically brightest known
(B=14.5-18.5). Despite the ability of 2-10 keV X-rays to penetrate large column
densities, we find BALQSOs to be extremely weak sources above 2 keV, and we are
only able to add two new 2-10 keV detections (0226-104 and IRAS 07598+6508) to
those previously reported. By comparison with non-BALQSOs of similar optical
continuum magnitudes, we derive the column densities needed to suppress the
expected X-ray fluxes of our BALQSOs. In several cases we derive column
densities > 5x10^{23} cm^{-2} for a neutral absorber with solar abundances.
These are the largest X-ray column densities yet inferred for BALQSOs, and they
exceed ROSAT lower limits by about an order of magnitude. Optical brightness
does not appear to be a good predictor of 2-10 keV brightness for BALQSOs, but
our data do suggest that the BALQSOs with high optical continuum polarizations
may be the X-ray brighter members of the class. For example, the highly
polarized object PHL 5200 appears to be unusually X-ray bright for a BALQSO
given its optical magnitude. We discuss the implications of our results for
future observations with AXAF and XMM. If the objects in our sample are
representative of the BALQSO population, precision X-ray spectroscopy of most
BALQSOs will unfortunately prove difficult in the near future.Comment: 19 pages, ApJ in press, also available from
http://www.astro.psu.edu/users/niel/papers/papers.htm
Systematic Review on the Management of Chronic Constipation in North America
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72642/1/j.1572-0241.2005.50613_2.x.pd
Differences Between The Optical/Uv Spectra Of X-Ray Bright And X-Ray Faint QSOs
We contrast measurements of composite optical and ultraviolet (UV) spectra
constructed from samples of QSOs defined by their soft X-ray brightness. X-ray
bright (XB) composites show stronger emission lines in general, but
particularly from the narrow line region. The difference in the [OIII]/Hbeta
ratio is particularly striking, and even more so when blended FeII emission is
properly subtracted. The correlation of this ratio with X-ray brightness were
principal components of QSO spectral diversity found by Boroson & Green (1992).
We find here that other, much weaker narrow optical forbidden lines ([OII] and
NeV) are enhanced by factors of 2 to 3 in our XB composites, and that narrow
line emission is also strongly enhanced in the XB UV composite. Broad permitted
line fluxes are slightly larger for all XB spectra, but the narrow/broad line
ratio stays similar or increases strongly with X-ray brightness for all strong
permitted lines except Hbeta.
Spectral differences between samples divided by their relative X-ray
brightness (as measured by alpha_{ox}) exceed those seen between complementary
samples divided by luminosity or radio loudness. We propose that the Baldwin
effect may be a secondary correlation to the primary relationship between
alpha_{ox} and emission line equivalent width. We conclude that either 1)
equivalent width depends strongly on the SHAPE of the ionizing continuum, as
crudely characterized here by alpha_{ox} or 2) both equivalent width and
alpha_{ox} are related to some third parameter characterizing the QSO physics.
One such possibility is intrinsic warm absorption; a soft X-ray absorber
situated between the broad and narrow line regions can successfully account for
many of the properties observed.Comment: 16 pages including 3 figures, AAS latex, plus 4 tables totaling 5
pages, to appear in ApJ Vol. 498, May 1, 199
Anomalous magnetic response of the spin-one-half Falicov-Kimball model
The infinite-dimensional spin one-half Falicov-Kimball model in an external
magnetic field is solved exactly. We calculate the magnetic susceptibility in
zero field, and the magnetization as a function of the field strength. The
model shows an anomalous magnetic response from thermally excited local moments
that disappear as the temperature is lowered. We describe possible real
materials that may exhibit this kind of anomalous behavior.Comment: 17 pages, 6 encapsulated postscript figures (included), submitted to
Phys. Rev.
On the Nature of Soft X-ray Weak Quasi-Stellar Objects
Recent studies of QSOs with ROSAT suggest the existence of a significant
population of Soft X-ray Weak QSOs (SXW QSOs) where the soft X-ray flux is ~
10-30 times smaller than in typical QSOs. As a first step in a systematic study
of these objects, we establish a well-defined sample of SXW QSOs which includes
all alpha_ox<=-2 QSOs from the Boroson & Green (1992) sample of 87 BQS QSOs.
SXW QSOs comprise about 11% of this optically selected QSO sample. From an
analysis of CIV absorption in the 55 BG92 QSOs with available CIV data, we find
a remarkably strong correlation between alpha_ox and the CIV absorption
equivalent width. This correlation suggests that absorption is the primary
cause of soft X-ray weakness in QSOs, and it reveals a continuum of absorption
properties connecting unabsorbed QSOs, X-ray warm absorber QSOs, SXW QSOs and
BAL QSOs. From a practical point of view, our correlation demonstrates that
selection by soft X-ray weakness is an effective (>=80% successful) and
observationally inexpensive way to find low-redshift QSOs with strong and
interesting ultraviolet absorption. We have also identified several notable
differences between the optical emission-line properties of SXW QSOs and those
of the other BG92 QSOs. SXW QSOs show systematically low [O III] luminosities
as well as distinctive H-beta profiles. They tend to lie toward the weak-[O
III] end of BG92 eigenvector 1, as do many low-ionization BAL QSOs. Unabsorbed
Seyferts and QSOs with similar values of eigenvector 1 have been suggested to
have extreme values of a primary physical parameter, perhaps mass accretion
rate relative to the Eddington rate (M-dot/M-dot_{Edd}). If these suggestions
are correct, it is likely that SXW QSOs also tend to have generally high values
of (M-dot/M-dot_{Edd}). (Abridged)Comment: 34 pages, ApJ accepted, also available from
http://www.astro.psu.edu/users/niel/papers/papers.htm
Space-Time Distribution of G-Band and Ca II H-Line Intensity Oscillations in Hinode/SOT-FG Observations
We study the space-time distributions of intensity fluctuations in 2 - 3 hour
sequences of multi-spectral, high-resolution, high-cadence broad-band
filtergram images (BFI) made by the SOT-FG system aboard the Hinode spacecraft.
In the frequency range 5.5 < f < 8.0 mHz both G-band and Ca II H-line
oscillations are suppressed in the presence of magnetic fields, but the
suppression disappears for f > 10 mHz. By looking at G-band frequencies above
10 mHz we find that the oscillatory power, both at these frequencies and at
lower frequencies too, lies in a mesh pattern with cell scale 2 - 3 Mm, clearly
larger than normal granulation, and with correlation times on the order of
hours. The mesh pattern lies in the dark lanes between stable cells found in
time-integrated G-band intensity images. It also underlies part of the bright
pattern in time-integrated H-line emission. This discovery may reflect
dynamical constraints on the sizes of rising granular convection cells together
with the turbulence created in strong intercellular downflows.Comment: 24 pages, 15 figure
The Spectral Energy Distribution and Emission-Line properties of the NLS1 Galaxy Arakelian 564
We present the intrinsic spectral energy distribution (SED) of the NLS1
Arakelian 564, constructed with contemporaneous data obtained during a
multi-wavelength, multi-satellite observing campaign in 2000 and 2001. We
compare it with that of the NLS1 Ton S180 and with those obtained for BLS1s to
infer how the relative accretion rates vary among the Sy1 population. Although
the peak of the SED is not well constrained, most of the energy is emitted in
the 10-100 eV regime, constituting roughly half of the emitted energy in the
optical/X-ray ranges. This is consistent with a primary spectral component
peaking in the extreme UV/soft X-ray band, and disk-corona models, hence high
accretion rates. Indeed, we estimate that \dot{m}~1. We examine the emission
lines in its spectrum, and we constrain the physical properties of the
line-emitting gas through photoionization modeling. The line-emitting gas is
characterized by log n~11 and log U~0, and is stratified around log U~0. Our
estimate of the radius of the H\beta-emitting region ~10 \pm 2 lt-days is
consistent with the radius-luminosity relationships found for Sy1 galaxies. We
also find evidence for super-solar metallicity in this NLS1. We show that the
emission lines are not good diagnostics for the underlying SEDs and that the
absorption line studies offer a far more powerful tool to determine the
ionizing continuum of AGNs, especially if comparing the lower- and
higher-ionization lines.Comment: 15 pages, 10 figures; accepted for publication in The Astrophysical
Journal, LaTeX emulateapj.st
The London theory of the crossing-vortex lattice in highly anisotropic layered superconductors
A novel description of Josephson vortices (JVs) crossed by the pancake
vortices (PVs) is proposed on the basis of the anisotropic London theory. The
field distribution of a JV and its energy have been calculated for both dense
() PV lattices with distance
between PVs, and the nonlinear JV core size . It is shown that the
``shifted'' PV lattice (PVs displaced mainly along JVs in the crossing vortex
lattice structure), formed in high out-of-plane magnetic fields transforms into
the PV lattice ``trapped'' by the JV sublattice at a certain field, lower than
, where is the flux quantum, is the
anisotropy parameter and is the distance between CuO planes.
With further decreasing , the free energy of the crossing vortex lattice
structure (PV and JV sublattices coexist separately) can exceed the free energy
of the tilted lattice (common PV-JV vortex structure) in the case of with the in-plane penetration depth if the low
() or high ()
in-plane magnetic field is applied. It means that the crossing vortex structure
is realized in the intermediate field orientations, while the tilted vortex
lattice can exist if the magnetic field is aligned near the -axis and the
-plane as well. In the intermediate in-plane fields
, the
crossing vortex structure with the ``trapped'' PV sublattice seems to settle in
until the lock-in transition occurs since this structure has the lower energy
with respect to the tilted vortex structure in the magnetic field
oriented near the -plane.Comment: 15 pages, 6 figures, accepted for publication in PR
X-ray Signatures of an Ionized Reprocessor in the Seyfert galaxy Ton S 180
We discuss the hard X-ray properties of the Seyfert galaxy Ton S 180, based
upon the analysis of ASCA data. We find the X-ray flux varied by a factor ~2 on
a time scale of a few thousand seconds. The source showed significantly higher
amplitude of variability in the 0.5-2 keV band than in the 2-10 keV band. The
continuum is adequately parameterized as a Gamma ~ 2.5 power-law across the
0.6--10 keV band . We confirm the recent discovery of an emission line of high
equivalent width, due to Fe K-shell emission from highly-ionized material.
These ASCA data show the Fe line profile to be broad and asymmetric and
tentatively suggest it is stronger during the X-ray flares, consistent with an
origin from the inner parts of an accretion disk. The X-ray spectrum is complex
below 2 keV, possibly due to emission from a blend of soft X-ray lines, which
would support the existence of an ionized reprocessor, most likely due to a
relatively high accretion rate in this source.Comment: 24 pages, 8 figures. LaTeX with encapsulated postscript. To appear in
the Astrophysical Journa
Initial data for Einstein's equations with superposed gravitational waves
A method is presented to construct initial data for Einstein's equations as a
superposition of a gravitational wave perturbation on an arbitrary stationary
background spacetime. The method combines the conformal thin sandwich formalism
with linear gravitational waves, and allows detailed control over
characteristics of the superposed gravitational wave like shape, location and
propagation direction. It is furthermore fully covariant with respect to
spatial coordinate changes and allows for very large amplitude of the
gravitational wave.Comment: Version accepted by PRD; added convergence plots, expanded
discussion. 9 pages, 9 figure
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