5,401 research outputs found
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
Physical Conditions in the Inner Narrow-Line Region of the Seyfert 2 Galaxy NGC 1068
The physical conditions in the inner narrow line region (NLR) of the Seyfert
2 galaxy, NGC 1068, are examined using ultraviolet and optical spectra and
photoionization models. The spectra are Hubble Space Telescope (HST) Harchive
data obtained with the Faint Object Spectrograph (FOS). We selected spectra of
four regions, taken through the 0.3" FOS aperture, covering the full FOS 1200A
to 6800A waveband. Each region is approximately 20 pc in extent, and all are
within 100 pc of the apparent nucleus of NGC 1068. The spectra show similar
emission-line ratios from wide range of ionization states for the most abundant
elements. After extensive photoionization modeling, we interpret this result as
an indication that each region includes a range of gas densities, which we
included in the models as separate components. Supersolar abundances were
required for several elements to fit the observed emission line ratios. Dust
was included in the models but apparently dust to gas fraction varies within
these regions. The low ionization lines in these spectra can be best explained
as arising in gas that is partially shielded from the ionizing continuum.
Although the predicted line ratios from the photoionization models provide a
good fit to the observed ratios, it is apparent that the model predictions of
electron temperatures in the ionized gas are too low. We interpret this as an
indication of additional collisional heating due to shocks and/or energetic
particles associated with the radio jet that traverses the NLR of NGC 1068. The
density structure within each region may also be the result of compression by
the jet.Comment: 38 pages, Latex, includes 5 figures (postscript), to appear in Ap
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
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
Virus Sharing, Genetic Sequencing, and Global Health Security
The WHO’s Pandemic Influenza Preparedness (PIP) Framework was a milestone global agreement designed to promote the international sharing of biological samples to develop vaccines, while that ensuring poorer countries would have access to those vaccines. Since the PIP Framework was negotiated, scientists have developed the capacity to use genetic sequencing data (GSD) to develop synthetic viruses rapidly for product development of life-saving technologies in a time-sensitive global emergency—threatening to unravel the Framework. Access to GSD may also have major implications for biosecurity, biosafety, and intellectual property (IP).
By rendering the physical transfer of viruses antiquated, GSD may also undermine the effectiveness of the PIP Framework itself, with disproportionate impacts on poorer countries. We examine the changes that need to be made to the PIP Framework to address the growing likelihood that GSD might be shared instead of physical virus samples. We also propose that the international community harness this opportunity to expand the scope of the PIP Framework beyond only influenza viruses with pandemic potential.
In light of non-influenza pandemic threats such as the Middle East Respiratory Syndrome (MERS) and Ebola, we call for an international agreement on the sharing of the benefits of research – such as vaccines and treatments – for other infectious diseases to ensure not only a more secure and healthy world, but also a more just world, for humanity
Heavy baryons
We review the experimental and theoretical status of baryons containing one
heavy quark. The charm and bottom baryon states are classified and their mass
spectra are listed. The appropriate theoretical framework for the description
of heavy baryons is the Heavy Quark Effective Theory, whose general ideas and
methods are introduced and illustrated in specific examples. We present simple
covariant expressions for the spin wave functions of heavy baryons including
p--wave baryons. The covariant spin wave functions are used to determine the
Heavy Quark Symmetry structure of flavour--changing current--induced
transitions between heavy baryons as well as one--pion and one--photon
transitions between heavy baryons of the same flavour. We discuss
corrections to the current--induced transitions as well as the structure of
heavy to light baryon transitions. Whenever possible we attempt to present
numbers to compare with experiment by making use of further model--dependent
assumptions as e.g. the constituent picture for light quarks. We highlight
recent advances in the theoretical understanding of the inclusive decays of
hadrons containing one heavy quark including polarization. For exclusive
semileptonic decays we discuss rates, angular decay distributions and
polarization effects. We provide an update of the experimental and theoretical
status of lifetimes of heavy baryons and of exclusive nonleptonic two body
decays of charm baryons.Comment: 93 pages, 18 figures not included, latex, DESY 94-095, MZ-THEP-94-0
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