175 research outputs found
Drug-Drug Interactions Among Hepatitis C Virus (HCV) and Human Immunodeficiency Virus (HIV) Medications
One-fourth of individuals diagnosed with the human immunodeficiency virus concomitantly have the hepatitis C virus infection. Since the discovery of highly active antiretroviral therapy, liver complications have become the leading cause of morbidity and mortality in HIV-HCV coinfected individuals. Optimal treatment in this patient population is critical, as coinfection has been linked to deterioration of both disease states. The objective of this review article is to highlight the current literature on drug-drug interactions between HIV and HCV treatments. The management of the treatment of coinfection patients has been covered extensively in numerous other publications
On the relativistic iron line and soft excess in the Seyfert 1 galaxy Markarian 335
We report on a 133 ks XMM-Newton observation of the Seyfert 1 galaxy
Markarian 335. The 0.4-12 keV spectrum contains an underlying power law
continuum, a soft excess below 2 keV, and a double-peaked iron emission feature
in the 6-7 keV range. We investigate the possibility that the double-peaked
emission might represent the characteristic signature of the accretion disc.
Detailed investigations show that a moderately broad, accretion disc line is
most likely present, but that the peaks may be owing to narrower components
from more distant material. The peaks at 6.4 and 7 keV can be identified,
respectively, with the molecular torus in active galactic nucleus unification
schemes, and very highly ionized, optically thin gas filling the torus. The
X-ray variability spectra on both long (~100 ks) and short (~1 ks) timescales
disfavour the recent suggestion that the soft excess is an artifact of
variable, moderately ionized absorption.Comment: 6 pages, 2 figures, accepted for publication in MNRA
A Cutoff in the X-ray Fluctuation Power Density Spectrum of the Seyfert 1 Galaxy NGC 3516
During 1997 March-July, XTE observed the bright, strongly variable Seyfert 1
galaxy NGC 3516 once every ~12.8 hr for 4.5 months and nearly continuously
(with interruptions due to SAA passage but not Earth occultation) for a 4.2 day
period in the middle. These were followed by ongoing monitoring once every ~4.3
days. These data are used to construct the first well-determined X-ray
fluctuation power density spectrum (PDS) of an active galaxy to span more than
4 decades of usable temporal frequency. The PDS shows no signs of any strict or
quasi-periodicity, but does show a progressive flattening of the power-law
slope from -1.74 at short time scales to -0.73 at longer time scales. This is
the clearest observation to date of the long-predicted cutoff in the PDS. The
characteristic variability time scale corresponding to this cutoff temporal
frequency is 1 month. Although it is unclear how this time scale may be
interpreted in terms of a physical size or process, there are several promising
candidate models. The PDS appears similar to those seen for Galactic black hole
candidates such as Cyg X-1, suggesting that these two classes of objects with
very different luminosities and putative black hole masses (differing by more
than a factor of 10^5) may have similar X-ray generation processes and
structures.Comment: 21 pages, incl. 5 figures, AASTe
Evidence for Relativistic Outflows in Narrow-line Seyfert 1 Galaxies
We report the observation of features near 1 keV in the ASCA spectra from
three ``Narrow Line Seyfert 1'' (NLS1) galaxies. We interpret these as oxygen
absorption in a highly relativistic outflow. If interpreted as absorption
edges, the implied velocities are 0.2--0.3c, near the limit predicted by
``line-locking'' radiative acceleration. If instead interpreted as broad
absorption lines, the implied velocities are ~0.57c, interestingly near the
velocity of particles in the last stable orbit around a Kerr black hole,
although a physical interpretation of this is not obvious. The features are
reminiscent of the UV absorption lines seen in broad absorption line quasars
(BALQSOs), but with larger velocities, and we note the remarkable similarities
in the optical emission line and broad band properties of NLS1s and
low-ionization BALQSOs.Comment: 9 pages using (AASTeX) aaspp4.sty and 2 Postscript figures. Accepted
for publication in Astrophysical Journal Letter
X-ray Surface Brightness Profiles of Active Galactic Nuclei in the Extended Groth Strip: Implications for AGN Feedback
Using data from the All Wavelength Extended Groth Strip International Survey
(AEGIS) we statistically detect the extended X-ray emission in the interstellar
medium (ISM)/intra-cluster medium (ICM) in both active and normal galaxies at
0.3 <= z <= 1.3. For both active galactic nuclei (AGN) host galaxy and normal
galaxy samples that are matched in restframe color, luminosity, and redshift
distribution, we tentatively detect excess X-ray emission at scales of 1--10
arcsec at a few sigma significance in the surface brightness profiles. The
exact significance of this detection is sensitive to the true characterization
of Chandra's point spread function. The observed excess in the surface
brightness profiles is suggestive of lower extended emission in AGN hosts
compared to normal galaxies. This is qualitatively similar to theoretical
predictions of the X-ray surface brightness profile from AGN feedback models,
where feedback from AGN is likely to evacuate the gas from the center of the
galaxy/cluster. We propose that AGN that are intrinsically under-luminous in
X-rays, but have equivalent bolometric luminosities to our sources will be the
ideal sample to study more robustly the effect of AGN feedback on diffuse
ISM/ICM gas.Comment: Accepted in PAS
AEGIS: Chandra Observation of DEEP2 Galaxy Groups and Clusters
We present a 200 ksec Chandra observation of seven spectroscopically
selected, high redshift (0.75 < z < 1.03) galaxy groups and clusters discovered
by the DEEP2 Galaxy Redshift Survey in the Extended Groth Strip (EGS). X-ray
emission at the locations of these systems is consistent with background. The
3-sigma upper limits on the bolometric X-ray luminosities (L_X) of these
systems put a strong constraint on the relation between L_X and the velocity
dispersion of member galaxies sigma_gal at z~1; the DEEP2 systems have lower
luminosity than would be predicted by the local relation. Our result is
consistent with recent findings that at high redshift, optically selected
clusters tend to be X-ray underluminous. A comparison with mock catalogs
indicates that it is unlikely that this effect is entirely caused by a
measurement bias between sigma_gal and the dark matter velocity dispersion.
Physically, the DEEP2 systems may still be in the process of forming and hence
not fully virialized, or they may be deficient in hot gas compared to local
systems. We find only one possibly extended source in this Chandra field, which
happens to lie outside the DEEP2 coverage.Comment: 5 pages, 3 figures. Accepted for publication in AEGIS ApJ Letters
special editio
AEGIS: New Evidence Linking Active Galactic Nuclei to the Quenching of Star Formation
Utilizing Chandra X-ray observations in the All-wavelength Extended Groth
Strip International Survey (AEGIS) we identify 241 X-ray selected Active
Galactic Nuclei (AGNs, L > 10^{42} ergs/s) and study the properties of their
host galaxies in the range 0.4 < z < 1.4. By making use of infrared photometry
from Palomar Observatory and BRI imaging from the Canada-France-Hawaii
Telescope, we estimate AGN host galaxy stellar masses and show that both
stellar mass and photometric redshift estimates (where necessary) are robust to
the possible contamination from AGNs in our X-ray selected sample. Accounting
for the photometric and X-ray sensitivity limits of the survey, we construct
the stellar mass function of X-ray selected AGN host galaxies and find that
their abundance decreases by a factor of ~2 since z~1, but remains roughly flat
as a function of stellar mass. We compare the abundance of AGN hosts to the
rate of star formation quenching observed in the total galaxy population. If
the timescale for X-ray detectable AGN activity is roughly 0.5-1 Gyr--as
suggested by black hole demographics and recent simulations--then we deduce
that the inferred AGN "trigger" rate matches the star formation quenching rate,
suggesting a link between these phenomena. However, given the large range of
nuclear accretion rates we infer for the most massive and red hosts, X-ray
selected AGNs may not be directly responsible for quenching star formation.Comment: 12 pages. Submitted to ApJ. Comments welcom
The Ionized Gas and Nuclear Environment in NGC 3783 V. Variability and Modeling of the Intrinsic Ultraviolet Absorption
We present results on the location, physical conditions, and geometry of the
outflow in the Seyfert 1 galaxy NGC 3783 from a study of the variable intrinsic
UV absorption. Based on 18 observations with HST/STIS and 6 observations with
FUSE, we find: 1) The absorption from the lowest-ionization species in each of
the three strong kinematic components varied inversely with the continuum flux,
indicating the ionization structure responded to changes in the photoionizing
flux over the weekly timescales sampled by our observations. 2) A multi-
component model with an unocculted NLR and separate BLR and continuum
line-of-sight covering factors predicts saturation in several lines, consistent
with the lack of observed variability. 3) Column densities for the individual
metastable levels are measured from the resolved C III *1175 absorption complex
observed in one component. Based on our computed metastable level populations,
the electron density of this absorber is ~3x10^4 cm^-3. Photoionization
modeling results place it at ~25 pc from the central source. 4) Using
time-dependent calculations, we are able to reproduce the detailed variability
observed in this absorber, and derive upper limits on the distances for the
other components of 25-50 pc. 5) The ionization parameters derived for the
higher ionization UV absorbers are consistent with the modeling results for the
lowest-ionization X-ray component, but with smaller total column density. They
have similar pressures as the three X-ray ionization components. These results
are consistent with an inhomogeneous wind model for the outflow in NGC 3783. 6)
Based on the predicted emission-line luminosities, global covering factor
constraints, and distances derived for the UV absorbers, they may be identified
with emission- line gas observed in the inner NLR of AGNs. (abridged)Comment: 30 pages, 18 figures (7 color), emulateapj, accepted for publication
in The Astrophysical Journa
The Ionized Gas and Nuclear Environment in NGC 3783. I. Time-Averaged 900 ks Chandra Grating Spectroscopy
We present results from a 900 ks exposure of NGC 3783 with the High-Energy
Transmission Grating Spectrometer on board the Chandra X-ray Observatory. The
resulting X-ray spectrum has the best combination of signal-to-noise and
resolution ever obtained for an AGN. This spectrum reveals absorption lines
from H-like and He-like ions of N, O, Ne, Mg, Al, Si, and S. There are also
possible absorption lines from H-like and He-like Ar and Ca. We also identify
inner-shell absorption from lower-ionization ions such as Si_VII-Si_XII and
S_XII-S_XIV. The iron absorption spectrum is very rich; L-shell lines of
Fe_XVII-Fe_XXIV are detected, strong complex of M-shell lines, and probable
resonance lines from Fe_XXV. The absorption lines are blueshifted relative to
the systemic velocity by a mean velocity of -590+-150 km/s. We resolve many of
the absorption lines, and their mean FWHM is 820+-280 km/s. We do not find
correlations between the velocity shifts or the FWHMs with the ionization
potentials of the ions. Most absorption lines show asymmetry, having more
extended blue wings than red wings. In O_VII we have resolved this asymmetry to
be from an additional absorption system at ~ -1300 km/s. The two X-ray
absorption systems are consistent in velocity shift and FWHM with the ones
identified in the UV lines of C IV, N V, and H I. Equivalent width measurements
for all lines are given and column densities are calculated for several ions.
We resolve the narrow Fe_K\alpha line at 6398.2+-3.3 eV to have a FWHM of
1720+-360 km/s, which suggests that this narrow line may be emitted from the
outer part of the broad line region or the inner part of the torus. We also
detect a `Compton shoulder' redward of the narrow Fe_K\alpha line which
indicates that it arises in cold, Compton-thick gas.Comment: 19 pages, 12 figures (2 in color), emulateapj5, accepted for
publication in The Astrophysical Journal Supplement
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