2,613 research outputs found
Significant X-ray Line Emission in the 5-6 keV band of NGC 4051
A Suzaku X-ray observation of NGC 4051 taken during 2005 Nov reveals line
emission at 5.44 keV in the rest-frame of the galaxy which does not have an
obvious origin in known rest-frame atomic transitions. The improvement to the
fit statistic when this line is accounted for establishes its reality at >99.9%
confidence: we have also verified that the line is detected in the three XIS
units independently. Comparison between the data and Monte Carlo simulations
shows that the probability of the line being a statistical fluctuation is p <
3.3 x 10^-4. Consideration of three independent line detections in Suzaku data
taken at different epochs yields a probability p< 3 x 10^-11 and thus
conclusively demonstrates that it cannot be a statistical fluctuation in the
data. The new line and a strong component of Fe Ka emission from neutral
material are prominent when the source flux is low, during 2005. Spectra from
2008 show evidence for a line consistent with having the same flux and energy
as that observed during 2005, but inconsistent with having a constant
equivalent width against the observed continuum. The stability of the line flux
and energy suggests that it may not arise in transient hotspots, as has been
suggested for similar lines in other sources, but could arise from a special
location in the reprocessor, such as the inner edge of the accretion disk.
Alternatively, the line energy may be explained by spallation of Fe into Cr, as
discussed in a companion paper.Comment: 18 pages, accepted for publication by Ap
Transcapillary fluid shifts in head and neck tissues during and after simulated microgravity
To understand the mechanism, magnitude, and time course of facial puffiness that occurs in microgravity, seven male subjects were tilted 6 degrees head down for 8 hr, and all four Starling transcapillary pressures were directly measured before, during, and after tilt. Head-down tilt (HDT) caused facial edema and a significant elevation of microvascular pressures measured in the lower lip: capillary pressures increased from 27.2 +/- 5 mm Hg pre-HDT to 33.9 +/- 1.7 mm Hg by the end of tilt. Subcutaneous and intramuscular interstitial fluid pressures in the neck also increased as a result of HDT, while interstitial fluid colloid osmotic pressures remained unchanged. Plasma colloid osmotic pressures dropped significantly after 4 hr of HDT, suggesting a transition from fluid filtration to absorption in capillary beds between the heart and feet during HDT. After 4 hr of seated recovery from HDT, microvascular pressures remained significantly elevated by 5 to 8 mm Hg above baseline values, despite a significant HDT diuresis and the orthostatic challenge of an upright, seated posture. During the control (baseline) period, urine output was 46.7 ml/hr; during HDT, it was 126.5 ml/hr. These results indicate that facial edema resulting from HDT is primarily caused by elevated capillary pressures and decreased plasma colloid osmotic pressures. Elevation of cephalic capillary pressures sustained for 4 hr after HDT suggests that there is a compensatory vasodilation to maintain microvascular perfusion. The negativity of interstitial fluid pressures above heart level also has implications for the maintenance of tissue fluid balance in upright posture
Simultaneous X-ray and Ultraviolet spectroscopy of the Seyfert galaxy NGC 5548. III. X-ray time variability
The Seyfert 1 galaxy NGC 5548 was observed for a week by Chandra using both
the HETGS and LETGS spectrometers. In this paper we study the time variability
of the continuum radiation. During our observation, the source showed a gradual
increase in flux over four days, followed by a rapid decrease and flattening of
the light curve afterwards. Superimposed upon these relatively slow variations
several short duration bursts or quasi-periodic oscillations occured with a
typical duration of several hours and separation between 0.6-0.9 days. The
bursts show a delay of the hard X-rays with respect to the soft X-rays of a few
hours. We interprete these bursts as due to a rotating, fluctuating hot spot at
approximately 10 gravitational radii; the time delay of the hard X-rays from
the bursts agree with the canonical picture of Inverse Compton scattering of
the soft accretion disk photons on a hot medium that is relatively close to the
central black hole.Comment: 6 pages, 7 figures, accepted for publication in Astronomy and
Astrophysic
Resolved Spectroscopy of the Narrow-Line Region in NGC 1068. I. The Nature of the Continuum Emission
We present the first long-slit spectra of the Seyfert 2 galaxy NGC 1068
obtained by the Space Telescope Imaging Spectrograph (STIS); the spectra cover
the wavelength range 1150 - 10,270 Angstroms at a spatial resolution of 0.05 -
0.1 arcsec and a spectral resolving power of 1000. In this first paper, we
concentrate on the far-UV to near-IR continuum emission from the continuum
``hot spot'' and surrounding regions extending out to +/- 6 arcsec (+/-432 pc)
at a position angle of 202 degrees In addition to the broad emission lines
detected by spectropolarimetry, the hot spot shows the ``little blue bump'' in
the 2000 - 4000 Ang. range, which is due to Fe II and Balmer continuum
emission. The continuum shape of the hot spot is indistinguishable from that of
NGC 4151 and other Seyfert 1 galaxies. Thus, the hot spot is reflected emission
from the hidden nucleus, due to electron scattering (as opposed to
wavelength-dependent dust scattering). The hot spot is ~0.3 arcsec in extent
and accounts for 20% of the scattered light in the inner 500 pc. We are able to
deconvolve the extended continuum emission in this region into two components:
electron-scattered light from the hidden nucleus (which dominates in the UV)
and stellar light (which dominates in the optical and near-IR). The scattered
light is heavily concentrated towards the hot spot, is stronger in the
northeast, and is enhanced in regions of strong narrow-line emission. The
stellar component is more extended, concentrated southwest of the hot spot,
dominated by an old (> 2 x 10 Gyr) stellar population, and includes a nuclear
stellar cluster which is ~200 pc in extent.Comment: 32 pages, Latex, includes 11 figures (postscript), to appear in the
Astrophysical Journa
Observations of Outflowing UV Absorbers in NGC 4051 with the Cosmic Origins Spectrograph
We present new Hubble Space Telescope (HST)/Cosmic Origins Spectrograph
observations of the Narrow-Line Seyfert 1 galaxy NGC 4051. These data were
obtained as part of a coordinated observing program including X-ray
observations with the Chandra/High Energy Transmission Grating (HETG)
Spectrometer and Suzaku. We detected nine kinematic components of UV
absorption, which were previously identified using the HST/Space Telescope
Imaging Spectrograph. None of the absorption components showed evidence for
changes in column density or profile within the \sim 10 yr between the STIS and
COS observations, which we interpret as evidence of 1) saturation, for the
stronger components, or 2) very low densities, i.e., n_H < 1 cm^-3, for the
weaker components. After applying a +200 km s^-1 offset to the HETG spectrum,
we found that the radial velocities of the UV absorbers lay within the O VII
profile. Based on photoionization models, we suggest that, while UV components
2, 5 and 7 produce significant O VII absorption, the bulk of the X-ray
absorption detected in the HETG analysis occurs in more highly ionized gas.
Moreover, the mass loss rate is dominated by high ionization gas which lacks a
significant UV footprint.Comment: 41 pages, 10 Figures; accepted for publication in the Astrophysical
Journa
Dissimilatory nitrate reductionpathways in an oligotrophic aquatic ecosystem: spatial and temporal trends
Elevated nitrate (NO3−) concentrations can cause eutrophication, which may lead to harmful algal blooms, loss of habitat and reduction in biodiversity. Denitrification, a dissimilatory process that removes NO3− mainly as dinitrogen gas (N2), is believed to be the dominant NO3− removal pathway in aquatic ecosystems. Evidence suggests that a less well-studied process, dissimilatory nitrate reduction to ammonium (DNRA), which retains nitrogen (N) in the system, may also be important under favorable conditions. Using stable isotope tracers in sealed microcosms, we measured the potential for NO3− losses due to DNRA and denitrification in an oligotrophic freshwater ecosystem. We took sediment and water samples at runoff and baseflow, across several ecotypes. Our objective was to quantify the relative importance of DNRA compared to denitrification with changes in ecotype and season. Potential denitrification rates ranged from 0 to 0.14 ± 0.03 µgN gAFDM−1 d−1. Potential DNRA rates ranged from 0 to 0.0051 ± 0.0008 µgN gAFDM−1 d−1. Denitrification losses peaked at the inflow stream ecotype at 96.2% of total dissimilatory NO3− removal, whereas losses due to DNRA peaked in the lake ecotype at 34.4%. When averaged over the entire system, denitrification peaked at baseflow (31.2%), while DNRA peaked at runoff (2.9%). Although NO3− transformations due to denitrification were higher than DNRA in all ecotype and temporal comparisons, our results suggest that DNRA is also important under favorable conditions
Interpretation of UV Absorption Lines in SN1006
We present a theoretical interpretation of the broad silicon and iron UV
absorption features observed with the Hubble Space Telescope in the spectrum of
the Schweizer-Middleditch star behind the remnant of Supernova 1006. These
features are caused by supernova ejecta in SN1006. We propose that the
redshifted SiII2 1260 A feature consists of both unshocked and shocked SiII.
The sharp red edge of the line at 7070 km/s indicates the position of the
reverse shock, while its Gaussian blue edge reveals shocked Si with a mean
velocity of 5050 km/s and a dispersion of 1240 km/s, implying a reverse shock
velocity of 2860 km/s. The measured velocities satisfy the energy jump
condition for a strong shock, provided that all the shock energy goes into
ions, with little or no collisionless heating of electrons. The line profiles
of the SiIII and SiIV absorption features indicate that they arise mostly from
shocked Si. The total mass of shocked and unshocked Si inferred from the SiII,
SiIII and SiIV profiles is M_Si = 0.25 \pm 0.01 Msun on the assumption of
spherical symmetry. Unshocked Si extends upwards from 5600 km/s. Although there
appears to be some Fe mixed with the Si at lower velocities < 7070 km/s, the
absence of FeII absorption with the same profile as the shocked SiII suggests
little Fe mixed with Si at higher (before being shocked) velocities. The column
density of shocked SiII is close to that expected for SiII undergoing steady
state collisional ionization behind the reverse shock, provided that the
electron to SiII ratio is low, from which we infer that most of the shocked Si
is likely to be of a fairly high degree of purity, unmixed with other elements.
We propose that the ambient interstellar density on the far side of SN1006 is
anomalously low compared to the density around the rest of the remnant. ThisComment: 24 pages, with 8 figures included. Accepted for publication in the
Astrophysical Journa
Moving beyond the ‘language problem': developing an understanding of the intersections of health, language and immigration status in interpreter-mediated health encounters
Health systems internationally are dealing with greater diversity in patient populations. However the focus on ‘the language problem’ has meant little attention is paid to diversity within and between migrant populations; and how interpreted consultations are influenced by intersecting migratory, ethnicity and sociodemographic variables. Our analysis of the experiences of patients, health care providers and interpreters in Scotland evidences the need to move beyond language, addressing multiple hidden inequalities in health care access and provision that operate in both clinic and, especially, home-based settings. We call for a practice-evidenced research agenda promoting cultural communication across health care and home settings, acknowledging immigration status as a social determinant of health.
Sur le plan international, des systèmes de santé font face à une diversité croissante dans ses populations de patients. Cependant, l’accent sur ‘le problème de langue’ se traduit dans une manque d’attention à la diversité a l’intérieur même et entre des populations des migrants; et la façon par laquelle des variables migratoire, ethnique et sociodémographique influencent elles-mêmes des consultations interprétées. Notre analyse des expériences des patients, des professionnels fournissant de soins de santé et des interprètes offre des preuves du besoin de dépasser le problème de langue. Et en faisant cela, nous adressons des multiples inégalités, souvent cachées dans des contextes de soins de santé, dans les milieux clinique et domicile. Nous proposons un programme de recherche basé sur la pratique, qui favorise la communication culturelle dans des milieux clinique et domicile, et qui reconnait le statut d’immigration comme un déterminant social de la santé
On the Effects of Dissipative Turbulence on the Narrow Emission-Line Ratios in Seyfert Galaxies
We present a photoionization model study of the effects of micro-turbulence
and dissipative heating on emission lines for number and column densities,
elemental abundances, and ionizations typical for the narrow emission line
regions (NLRs) of Seyfert galaxies. Earlier studies of NLR spectra generally
found good agreement between the observations and the model predictions for
most strong emission lines, such as [O III] 5007, [O II]
3727, [N II] 6583, [Ne III] 3869, and the H and He
recombination lines. Nevertheless, the strengths of lines from species with
ionization potentials greater than that of He(54.4 eV), e.g. N and
Ne, were often under-predicted. Among the explanations suggested for
these discrepancies were (selectively) enhanced elemental abundances and
contributions from shock heated gas. Interestingly, the NLR lines have widths
of several 100 km s, well in excess of the thermal broadening. If this
is due to micro-turbulence, and the turbulence dissipates within the
emission-line gas, the gas can be heated in excess of that due to
photoionization. We show that the combined effects of turbulence and
dissipative heating can strongly enhance N V 1240 (relative to He II
1640), while the heating alone can boost the strength of [Ne V]
3426. We suggest that this effect is present in the NLR, particularly
within 100 pc of the central engine. Finally, since micro-turbulence
would make clouds robust against instabilities generated during acceleration,
it is not likely to be a coincidence that the radially outflowing emission-line
gas is turbulent.Comment: 29 oages, including 10 figures. Accepted for publication in the
Astrophysical Journa
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