1,353 research outputs found
1ES 1927+654: Persistent and rapid X-ray variability in an AGN with low intrinsic neutral X-ray absorption and narrow optical emission lines
We present X-ray and optical observations of the X-ray bright AGN 1ES
1927+654. The X-ray observations obtained with ROSAT and Chandra reveal
persistent, rapid and large scale variations, as well as steep 0.1-2.4 keV
(Gamma = 2.6 +/- 0.3) and 0.3-7.0 keV (Gamma = 2.7 +/- 0.2) spectra. The
measured intrinsic neutral X-ray column density is approximately 7e20cm^-2. The
X-ray timing properties indicate that the strong variations originate from a
region, a few hundred light seconds from the central black hole, typical for
type 1 AGN. High quality optical spectroscopy reveals a typical Seyfert 2
spectrum with some host galaxy contamination and no evidence of Fe II
multiplets or broad hydrogen Balmer wings. The intrinsic optical extinction
derived from the BLR and NLR are A_V >= 3.7 and A_V=1.7, respectively. The
X-ray observations give an A_V value of less than 0.58, in contrast to the
optical extinction values. We discuss several ideas to explain this apparent
difference in classification including partial covering, an underluminous BLR
or a high dust to gas ratio.Comment: 8 pages including 10 figures. Accepted for publication in Astronomy
and Astrophysic
Does Oral Gabapentin Administered Prior to Scheduled Cesarean Delivery Decrease Pain With Movement in Adult Women at 24 Hours as Compared to Placebo?
OBJECTIVE: The objective of this selective evidence based medicine review is to determine whether or not oral gabapentin administered prior to scheduled cesarean delivery decreases pain with movement in adult women at 24 hours postpartum as compared to placebo.
STUDY DESIGN: Review of three English language, peer-reviewed, primary studies published after 2000.
DATA SOURCES: Three randomized, placebo-controlled trials comparing the efficacy of oral gabapentin to a lactose placebo in adult women undergoing elective cesarean delivery. Sources were selected from PubMed, Medline, Ovid, and the Cochrane Database to include all studies matching the keywords that were published in peer-reviewed, English language journals after 2000 and included only women over 18 years of age.
OUTCOMES MEASURED: Primary outcome measured was patient reported pain perception on a 0-100mm Visual Analog Scale (VAS - 0 = no pain, 100 = worst possible pain) measured 24 hours post cesarean section. Satisfaction with pain management, as measured by a numerical rating scale (0-10) was considered secondarily.
RESULTS: Two of the three studies found significant improvement in post-cesarean delivery analgesia and satisfaction with analgesia with adjunctive gabapentin therapy at doses of 600mg and 300mg respectively. A third study investigated both dosages, but found no clinical benefit to either.
CONCLUSIONS: Evidence is inconclusive as to whether oral gabapentin administered prior to scheduled cesarean delivery decreases pain with movement in adult women at 24 hours postpartum as compared to placebo
Spectropolarimetry of the Luminous Narrow-Line Seyfert Galaxies IRAS 20181-2244 and IRAS 13224-3809
We observed the narrow-line Seyfert 1 galaxies IRAS 20181-2244 and IRAS
13324-3809 with a new spectropolarimeter on the RC spectrograph at the CTIO 4m
telescope. Previously it had been suggested that IRAS 20181-2244 was a Type 2
QSO and thus might contain an obscured broad-line region which could be
detected by the presence of broad Balmer lines in the polarized flux. We found
the object to be polarized at about 2%, and constant with wavelength, (unlike
most narrow-line Seyfert 1s), but with no evidence of broad Balmer lines in
polarized flux. The spectropolarimetry indicates that the scattering material
is inside the BLR. IRAS 13224-3809, notable for its high variability in X-ray
and UV wavelengths, has a low polarization consistent with a Galactic
interstellar origin.Comment: 19 pages using (AASTEX) aaspp4.sty and 5 postscript figures To be
published in the Astrophysical Journa
XMM-Newton observation of the ULIRG NGC 6240: The physical nature of the complex Fe K line emission
We report on an XMM-Newton observation of the ultraluminous infrared galaxy
NGC 6240. The 0.3-10 keV spectrum can be successfully modelled with: (i) three
collisionally ionized plasma components with temperatures of about 0.7, 1.4,
and 5.5 keV; (ii) a highly absorbed direct power-law component; and (iii) a
neutral Fe K_alpha and K_beta line. We detect a significant neutral column
density gradient which is correlated with the temperature of the three plasma
components. Combining the XMM-Newton spectral model with the high spatial
resolution Chandra image we find that the temperatures and the column densities
increase towards the center.
With high significance, the Fe K line complex is resolved into three distinct
narrow lines: (i) the neutral Fe K_alpha line at 6.4 keV; (ii) an ionized line
at about 6.7 keV; and (iii) a higher ionized line at 7.0 keV (a blend of the Fe
XXVI and the Fe K_beta line). While the neutral Fe K line is most probably due
to reflection from optically thick material, the Fe XXV and Fe XXVI emission
arises from the highest temperature ionized plasma component.
We have compared the plasma parameters of the ultraluminous infrared galaxy
NGC 6240 with those found in the local starburst galaxy NGC 253. We find a
striking similarity in the plasma temperatures and column density gradients,
suggesting a similar underlying physical process at work in both galaxies.Comment: 8 pages including 9 figures. Accepted for publication in A&
Central Masses and Broad-Line Region Sizes of Active Galactic Nuclei: I. Comparing the Photoionization and Reverberation Techniques
The masses and emission-line region sizes of Active Galactic Nuclei (AGNs)
can be measured by ``reverberation-mapping'' (measuring the lag of the
emission-line luminosity after changes in the continuum). We use tis technique
to calibrate similar size and mass estimates made by photoionization models of
the AGN line-emitting regions. We compile a sample of 19 AGNs with reliable
reverberation and spectroscopy data, twice the number available previously. The
data provide strong evidence that the BLR size and the emission-line width
measure directly the central mass. Two methods are used to estimate the
distance of the broad emission-line region (BLR) from the ionizing source: the
photoionization method (available for many AGNs but has large intrinsic
uncertainties), and the reverberation method (gives very reliable distances,
but available for only a few objects). The distance estimate is combined with
the velocity dispersion, derived from the broad Hb line profile, to estimate
the virial mass. Comparing the central masses calculated with the reverberation
method to those calculated using a photoionization model, we find a highly
significant, nearly linear correlation. This provides a calibration of the
photoionization method on the objects with presently available reverberation
data, which should enable mass estimates for all AGNs with measured Hb line
width. Comparing the BLR sizes given by the two methods also enables us to
estimate the ionizing EUV luminosity which is directly unobservable. We find it
to be typically ten times the visible (monochromatic luminosity at 5100A). The
inferred Eddington ratio of the individual objects in our sample are 0.001-0.03
(visible luminosity) and 0.01-0.3 (ionizing luminosity).Comment: 27 pages Latex, 8 figures. Accepted for publication in the
Astrophysical Journa
Optical Properties of Radio-selected Narrow Line Seyfert 1 Galaxies
We present results from the analysis of the optical spectra of 47
radio-selected narrow-line Seyfert 1 galaxies (NLS1s). These objects are a
subset of the First Bright Quasar Survey (FBQS) and were initially detected at
20 cm (flux density limit ~1 mJy) in the VLA FIRST Survey. We run Spearman rank
correlation tests on several sets of parameters and conclude that, except for
their radio properties, radio-selected NLS1 galaxies do not exhibit significant
differences from traditional NLS1 galaxies. Our results are also in agreement
with previous studies suggesting that NLS1 galaxies have small black hole
masses that are accreting very close to the Eddington rate. We have found 16
new radio-loud NLS1 galaxies, which increases the number of known radio-loud
NLS1 galaxies by a factor of ~5.Comment: 18 pages, 20 figures, Accepted for publication in Ap
Influence of the twospotted spider mite, Tetranychus urticae, on the gas exchange of Pinot noir grapevine leaves
The effect of feeding damage by the twospotted spider mite (Tetranychus urticae KOCH; Acari: Tetranychidae) on the gas exchange of grapevine leaves (Vitis vinifera L.; cv. Pinot noir) was investigated. In addition, the influence of some pesticides was studied. A significant reduction of the net CO2 assimilation, transpiration as well as stomatal and mesophyll conductance with increasing mite feeding damage were observed. At 6000 mite-days per leaf the 3rd and 9th main leaves (from the base) showed an average reduction in net CO2 assimilation of 52.2 % and 48.4 %, respectively, while the 6th leaf showed a reduction of only 21.3 %. The response of grapevine photosynthesis to mite feeding seems to depend not only on mite density and duration of feeding, but also on the phenological stage of the plant. In fact, at veraison the vines showed increased tolerance to mite feeding compared with other phenological stages. At mite infestation levels of 6000 mite-days, leaves infested with T. urticae showed, as compared to uninjured leaves, an average reduction in transpiration rate of 14.4 % to 40.8 %, depending on the leaf position. The acaricides Tetradifon and Fenbutatin-oxide and the fungicide Folpet combined with Penconazol showed no effect on the gas exchange parameters
Detailed Analysis of Balmer Lines in a Sloan Digital Sky Survey Sample of 90 Broad Line Active Galactic Nuclei
In order to contribute to the general effort aiming at the improvement of our
knowledge about the physical conditions within the Broad Line Region (BLR) of
Active Galactic Nuclei (AGN), here we present the results achieved by our
analysis of the spectral properties of a sample of 90 broad line emitting
sources, collected at the Sloan Digital Sky Survey (SDSS) database. By focusing
our attention mainly onto the Balmer series of hydrogen emission lines, which
is the dominant feature in the optical wavelength range of many BLR spectra, we
extracted several flux and profile measurements, which we related to other
source properties, such as optical continuum luminosities, inferred black hole
masses, and accretion rates. Using the Boltzmann Plot method to investigate the
Balmer line flux ratios as a function of the line profiles, we found that
broader line emitting AGN typically have larger H_alpha / H_beta and smaller
H_gamma / H_beta and H_delta / H_beta line ratios. With the help of some recent
investigations, we model the structure of the BLR and we study the influence of
the accretion process on the properties of the BLR plasma.Comment: 14 pages, 11 figures, fixes the wrong names of 4 objects; published
on Ap
Spectroscopic Properties of QSOs Selected from Ultraluminous Infrared Galaxy Samples
We performed spectroscopic observations for a large infrared QSO sample with
a total of 25 objects. The sample was compiled from the QDOT redshift survey,
the 1 Jy ULIRGs survey and a sample obtained by a cross-correlation study of
the IRAS Point Source Catalogue with the ROSAT All Sky Survey Catalogue.
Statistical analyses of the optical spectra show that the vast majority of
infrared QSOs have narrow permitted emission lines (with FWHM of Hbeta less
than 4000 km/s) and more than 60% of them are luminous narrow line Seyfert 1
galaxies. Two of the infrared QSOs are also classified as low ionization BAL
QSOs. More than 70% of infrared QSOs are moderately or extremely strong Fe II
emitters. This is the highest percentage of strong Fe II emitters in all
subclasses of QSO/Seyfert 1 samples. We found that the Fe II to Hbeta, line
ratio is significantly correlated with the [OIII]5007 peak and Hbeta blueshift.
Soft X-ray weak infrared QSOs tend to have large blueshifts in permitted
emission lines and significant Fe II48,49 (5100--5400 A) residuals relative to
the Boroson & Green Fe II template. If the blueshifts in permitted lines are
caused by outflows, then they appear to be common in infrared QSOs. As the
infrared-selected QSO sample includes both luminous narrow line Seyfert 1
galaxies and low ionization BAL QSOs, it could be a useful laboratory to
investigate the evolutionary connection among these objects.Comment: 35 pages,14 figures, 4 tables, accepted for publication in A
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