8,100 research outputs found
Ultraviolet/X-ray variability and the extended X-ray emission of the radio-loud broad absorption line quasar PG 1004+130
We present the results of recent Chandra, XMM-Newton, and Hubble Space
Telescope observations of the radio-loud (RL), broad absorption line (BAL)
quasar PG 1004+130. We compare our new observations to archival X-ray and UV
data, creating the most comprehensive, high signal-to-noise, multi-epoch,
spectral monitoring campaign of a RL BAL quasar to date. We probe for
variability of the X-ray absorption, the UV BAL, and the X-ray jet, on
month-year timescales. The X-ray absorber has a low column density of
cm when it is assumed to be fully
covering the X-ray emitting region, and its properties do not vary
significantly between the 4 observations. This suggests the observed absorption
is not related to the typical "shielding gas" commonly invoked in BAL quasar
models, but is likely due to material further from the central black hole. In
contrast, the CIV BAL shows strong variability. The equivalent width (EW) in
2014 is EW=11.240.56 \AA, showing a fractional increase of =1.160.11 from the 2003 observation, 3183 days earlier
in the rest-frame. This places PG 1004+130 among the most highly variable BAL
quasars. By combining Chandra observations we create an exposure 2.5 times
deeper than studied previously, with which to investigate the nature of the
X-ray jet and extended diffuse X-ray emission. An X-ray knot, likely with a
synchrotron origin, is detected in the radio jet ~8 arcsec (30 kpc) from the
central X-ray source with a spatial extent of ~4 arcsec (15 kpc). No similar
X-ray counterpart to the counterjet is detected. Asymmetric, non-thermal
diffuse X-ray emission, likely due to inverse Compton scattering of Cosmic
Microwave Background photons, is also detected.Comment: 15 pages, 7 figures, 3 tables. Accepted for publication in Ap
Effect of edge transmission and elastic scattering on the resistance of magnetic barriers
Strong magnetic barriers are defined in two-dimensional electron gases by
magnetizing dysprosium ferromagnetic platelets on top of a Ga[Al]As
heterostructure. A small resistance across the barrier is observed even deep
inside the closed regime. We have used semiclassical simulations to explain
this behavior quantitatively in terms of a combined effect of elastic electron
scattering inside the barrier region and E x B drift at the intersection of the
magnetic barrier with the edge of the Hall bar.Comment: 7 pages 4 figure
X-raying the Winds of Luminous Active Galaxies
We briefly describe some recent observational results, mainly at X-ray
wavelengths, on the winds of luminous active galactic nuclei (AGNs). These
winds likely play a significant role in galaxy feedback. Topics covered include
(1) Relations between X-ray and UV absorption in Broad Absorption Line (BAL)
and mini-BAL quasars; (2) X-ray absorption in radio-loud BAL quasars; and (3)
Evidence for relativistic iron K BALs in the X-ray spectra of a few bright
quasars. We also mention some key outstanding problems and prospects for future
advances; e.g., with the International X-ray Observatory (IXO).Comment: 7 pages, 3 figures, to appear in proceedings of the conference "The
Monster's Fiery Breath: Feedback in Galaxies, Groups, and Clusters", June
2009, Madison, Wisconsi
Thermopower of Two-Dimensional Electrons at = 3/2 and 5/2
The longitudinal thermopower of ultra-high mobility two-dimensional electrons
has been measured at both zero magnetic field and at high fields in the
compressible metallic state at filling factor and the
incompressible fractional quantized Hall state at . At zero field
our results demonstrate that the thermopower is dominated by electron diffusion
for temperatures below about mK. A diffusion dominated thermopower is
also observed at and allows us to extract an estimate of the
composite fermion effective mass. At both the temperature and
magnetic field dependence of the observed thermopower clearly signal the
presence of the energy gap of this fractional quantized Hall state. We find
that the thermopower in the vicinity of exceeds that recently
predicted under the assumption that the entropy of the 2D system is dominated
by non-abelian quasiparticle exchange statistics.Comment: 10 pages, 10 figures
Searching for additional heating - [OII] emission in the diffuse ionized gas of NGC891, NGC4631 and NGC3079
We present spectroscopic data of ionized gas in the disk--halo regions of
three edge-on galaxies, NGC 891, NGC 4631 and NGC 3079, covering a wavelength
range from [\ion{O}{2}] 3727\AA to [\ion{S}{2}] 6716.4\AA.
The inclusion of the [\ion{O}{2}] emission provides new constraints on the
properties of the diffuse ionized gas (DIG), in particular, the origin of the
observed spatial variations in the line intensity ratios. We used three
different methods to derive electron temperatures, abundances and ionization
fractions along the slit. The increase in the [\ion{O}{2}]/H line ratio
towards the halo in all three galaxies requires an increase either in electron
temperature or in oxygen abundance. Keeping the oxygen abundance constant
yields the most reasonable results for temperature, abundances, and ionization
fractions. Since a constant oxygen abundance seems to require an increase in
temperature towards the halo, we conclude that gradients in the electron
temperature play a significant role in the observed variations in the optical
line ratios from extraplanar DIG in these three spiral galaxies.Comment: 43 pages, 29 figure
Millimeter wave satellite concepts, volume 1
The identification of technologies necessary for development of millimeter spectrum communication satellites was examined from a system point of view. Development of methodology based on the technical requirements of potential services that might be assigned to millimeter wave bands for identifying the viable and appropriate technologies for future NASA millimeter research and development programs, and testing of this methodology with selected user applications and services were the goals of the program. The entire communications network, both ground and space subsystems was studied. Cost, weight, and performance models for the subsystems, conceptual design for point-to-point and broadcast communications satellites, and analytic relationships between subsystem parameters and an overall link performance are discussed along with baseline conceptual systems, sensitivity studies, model adjustment analyses, identification of critical technologies and their risks, and brief research and development program scenarios for the technologies judged to be moderate or extensive risks. Identification of technologies for millimeter satellite communication systems, and assessment of the relative risks of these technologies, was accomplished through subsystem modeling and link optimization for both point-to-point and broadcast applications
Ionization of Sodium and Rubidium nS, nP and nD Rydberg atoms by blackbody radiation
Results of theoretical calculations of ionization rates of Rb and Na Rydberg
atoms by blackbody radiation (BBR) are presented. Calculations have been
performed for nS, nP and nD states of Na and Rb, which are commonly used in a
variety of experiments, at principal quantum numbers n=8-65 and at three
ambient temperatures of 77, 300 and 600 K. A peculiarity of our calculations is
that we take into account the contributions of BBR-induced redistribution of
population between Rydberg states prior to photoionization and field ionization
by extraction electric field pulses. The obtained results show that these
phenomena affect both the magnitude of measured ionization rates and shapes of
their dependencies on n. The calculated ionization rates are compared with the
results of our earlier measurements of BBR-induced ionization rates of Na nS
and nD Rydberg states with n=8-20 at 300 K. A good agreement for all states
except nS with n>15 is observed. We also present the useful analytical formulae
for quick estimation of BBR ionization rates of Rydberg atoms.Comment: 14 pages, 6 figures, 6 tables in Appendi
Multi-scale analysis of compressible viscous and rotating fluids
We study a singular limit for the compressible Navier-Stokes system when the
Mach and Rossby numbers are proportional to certain powers of a small parameter
\ep. If the Rossby number dominates the Mach number, the limit problem is
represented by the 2-D incompressible Navier-Stokes system describing the
horizontal motion of vertical averages of the velocity field. If they are of
the same order then the limit problem turns out to be a linear, 2-D equation
with a unique radially symmetric solution. The effect of the centrifugal force
is taken into account
SDSS J075101.42+291419.1: A Super-Eddington Accreting Quasar with Extreme X-ray Variability
We report the discovery of extreme X-ray variability in a type 1 quasar: SDSS
J. It has a black hole mass of
measured from reverberation mapping (RM), and the black hole is accreting with
a super-Eddington accretion rate. Its XMM-Newton observation in 2015 May
reveals a flux drop by a factor of with respect to the Swift
observation in 2013 May when it showed a typical level of X-ray emission
relative to its UV/optical emission. The lack of correlated UV variability
results in a steep X-ray-to-optical power-law slope () of
-1.97 in the low X-ray flux state, corresponding to an X-ray weakness factor of
36.2 at rest-frame 2 keV relative to its UV/optical luminosity. The mild
UV/optical continuum and emission-line variability also suggest that the
accretion rate did not change significantly. A single power-law model modified
by Galactic absorption describes well the keV spectra of the X-ray
observations in general. The spectral fitting reveals steep spectral shapes
with . We search for active galactic nuclei (AGNs) with such
extreme X-ray variability in the literature and find that most of them are
narrow-line Seyfert 1 galaxies and quasars with high accretion rates. The
fraction of extremely X-ray variable objects among super-Eddington accreting
AGNs is estimated to be . We discuss two possible scenarios,
disk reflection and partial covering absorption, to explain the extreme X-ray
variability of SDSS J. We propose a possible origin for the
partial covering absorber, which is the thick inner accretion disk and its
associated outflow in AGNs with high accretion rates.Comment: 15 pages, 9 figures, accepted for publication in Ap
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