1,130 research outputs found
Determinants of the implementation of a new practice in hormonal contraception by Quebec nurses
Challenges of implementing task-shifting in contraceptive care--an experience in Quebec, Canada.
Iron K Lines from Gamma Ray Bursts
We present models for reprocessing of an intense flux of X-rays and gamma
rays expected in the vicinity of gamma ray burst sources. We consider the
transfer and reprocessing of the energetic photons into observable features in
the X-ray band, notably the K lines of iron. Our models are based on the
assumption that the gas is sufficiently dense to allow the microphysical
processes to be in a steady state, thus allowing efficient line emission with
modest reprocessing mass and elemental abundances ranging from solar to
moderately enriched. We show that the reprocessing is enhanced by
down-Comptonization of photons whose energy would otherwise be too high to
absorb on iron, and that pair production can have an effect on enhancing the
line production. Both "distant" reprocessors such as supernova or wind remnants
and "nearby" reprocessors such as outer stellar envelopes can reproduce the
observed line fluxes with Fe abundances 30-100 times above solar, depending on
the incidence angle. The high incidence angles required arise naturally only in
nearby models, which for plausible values can reach Fe line to continuum ratios
close to the reported values.Comment: 37 pages, 10 figures. Ap. J in pres
X-ray vs. Optical Variations in the Seyfert 1 Nucleus NGC 3516: A Puzzling Disconnectedness
We present optical broadband (B and R) observations of the Seyfert 1 nucleus
NGC 3516, obtained at Wise Observatory from March 1997 to March 2002,
contemporaneously with X-ray 2-10 keV measurements with RXTE. With these data
we increase the temporal baseline of this dataset to 5 years, more than triple
to the coverage we have previously presented for this object. Analysis of the
new data does not confirm the 100-day lag of X-ray behind optical variations,
tentatively reported in our previous work. Indeed, excluding the first year's
data, which drive the previous result, there is no significant correlation at
any lag between the X-ray and optical bands. We also find no correlation at any
lag between optical flux and various X-ray hardness ratios. We conclude that
the close relation observed between the bands during the first year of our
program was either a fluke, or perhaps the result of the exceptionally bright
state of NGC 3516 in 1997, to which it has yet to return. Reviewing the results
of published joint X-ray and UV/optical Seyfert monitoring programs, we
speculate that there are at least two components or mechanisms contributing to
the X-ray continuum emission up to 10 keV: a soft component that is correlated
with UV/optical variations on timescales >1 day, and whose presence can be
detected when the source is observed at low enough energies (about 1 keV), is
unabsorbed, or is in a sufficiently bright phase; and a hard component whose
variations are uncorrelated with the UV/optical.Comment: 9 pages, AJ, in pres
An extreme, blueshifted iron line profile in the Narrow Line Seyfert 1 PG 1402+261; an edge-on accretion disk or highly ionized absorption?
We report on a short XMM-Newton observation of the radio-quiet Narrow Line
Seyfert 1 PG 1402+261. The EPIC X-ray spectrum of PG 1402+261 shows a strong
excess of counts between 6-9 keV in the rest frame. This feature can be modeled
by an unusually strong (equivalent width 2 keV) and very broad (FWHM velocity
of 110000 km/s) iron K-shell emission line. The line centroid energy at 7.3 keV
appears blue-shifted with respect to the iron Kalpha emission band between
6.4-6.97 keV, while the blue-wing of the line extends to 9 keV in the quasar
rest frame. The line profile can be fitted by reflection from the inner
accretion disk, but an inclination angle of >60 deg is required to model the
extreme blue-wing of the line. Furthermore the extreme strength of the line
requires a geometry whereby the hard X-ray emission from PG 1402+261 above 2
keV is dominated by the pure-reflection component from the disk, while little
or none of the direct hard power-law is observed. Alternatively the spectrum
above 2 keV may instead be explained by an ionized absorber, if the column
density is sufficiently high (N_H > 3 x 10^23 cm^-2) and if the matter is
ionized enough to produce a deep (tau~1) iron K-shell absorption edge at 9 keV.
This absorber could originate in a large column density, high velocity outflow,
perhaps similar to those which appear to be observed in several other high
accretion rate AGN. Further observations, especially at higher spectral
resolution, are required to distinguish between the accretion disk reflection
or outflow scenarios.Comment: Accepted for publication in ApJ (18 pages, 5 figures, 1 table
A New Equilibrium for Accretion Disks Around Black Holes
Accretion disks around black holes in which the shear stress is proportional
to the total pressure, the accretion rate is more than a small fraction of
Eddington, and the matter is distributed smoothly are both thermally and
viscously unstable in their inner portions. The nonlinear endstate of these
instabilities is uncertain. Here a new inhomogeneous equilibrium is proposed
which is both thermally and viscously stable. In this equilibrium the majority
of the mass is in dense clumps, while a minority reaches temperatures K. The requirements of dynamical and thermal equilibrium completely
determine the parameters of this system, and these are found to be in good
agreement with the parameters derived from observations of accreting black
holes, both in active galactic nuclei and in stellar binary systems.Comment: AAS LaTeX, accepted to Ap. J. Letter
EXITE2 Observation of the SIGMA Source GRS 1227+025
We report the EXITE2 hard X-ray imaging of the sky around 3C273. A 2h
observation on May 8, 1997, shows a 260 mCrab source detected at
in each of two bands (50-70 and 70-93 keV) and located 30'
from 3C273 and consistent in position with the SIGMA source GRS1227+025. The
EXITE2 spectrum is consistent with a power law with photon index 3 and large
low energy absorption, as indicated by the GRANAT/SIGMA results. No source was
detected in more sensitive followup EXITE2 observations in 2000 and 2001 with
3 upper limits of 190 and 65 mCrab, respectively. Comparison with the
flux detected by SIGMA shows the source to be highly variable, suggesting it
may be non-thermal and beamed and thus the first example of a ``type 2''
(absorbed) Blazar. Alternatively it might be (an unprecedented) very highly
absorbed binary system undergoing accretion disk instability outbursts,
possibly either a magnetic CV, or a black hole X-ray nova.Comment: 12 pages, 4 figures, accepted for publication in Ap
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