1,997 research outputs found
Radio sources in the Chandra Galactic Bulge Survey
We discuss radio sources in the Chandra Galactic Bulge Survey region. By cross-matching the X-ray sources in this field with the NRAO VLA Sky Survey archival data, we find 12 candidate matches. We present a classification scheme for radio/X-ray matches in surveys taken in or near the Galactic plane, taking into account other multiwavelength data. We show that none of the matches found here is likely to be due to coronal activity from normal stars because the radio to X-ray flux ratios are systematically too high. We show that one of the source could be a radio pulsar, and that one could be a planetary nebula, but that the bulk of the sources are likely to be background active galactic nuclei (AGN), with many confirmed through a variety of approaches. Several of the AGN are bright enough in the near-infrared (and presumably in the optical) to use as probes of the interstellar medium in the inner Galaxy
Importance of site of infection and antibiotic selection in the treatment of carbapenem-resistant Pseudomonas aeruginosa sepsis
ABSTRACT
In a retrospective analysis of 215 patients with carbapenem-resistant
Pseudomonas aeruginosa
sepsis, we observed a significantly higher risk of mortality associated with respiratory tract infection (risk ratio [RR], 1.20; 95% confidence interval [CI], 1.04 to 1.39;
P
= 0.010) and lower risk with urinary tract infection (RR, 0.80; 95% CI, 0.71 to 0.90;
P
= 0.004). Aminoglycoside monotherapy was associated with increased mortality, even after adjusting for confounders (adjusted RR, 1.72; 95% CI, 1.03 to 2.85;
P
= 0.037), consistent across multiple sites of infection.
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The Chandra Galactic Bulge Survey: optical catalogue and point-source counterparts to X-ray sources
As part of the Chandra Galactic Bulge Survey (GBS), we present a catalogue of
optical sources in the GBS footprint. This consists of two regions centered at
Galactic latitude b = 1.5 degrees above and below the Galactic Centre, spanning
(l x b) = (6x1) degrees. The catalogue consists of 2 or more epochs of
observations for each line of sight in r', i' and H{\alpha} filters. It is
complete down to r' = 20.2 and i' = 19.2 mag; the mean 5{\sigma} depth is r' =
22.5 and i' = 21.1 mag. The mean root-mean-square residuals of the astrometric
solutions is 0.04 arcsec. We cross-correlate this optical catalogue with the
1640 unique X-ray sources detected in Chandra observations of the GBS area, and
find candidate optical counterparts to 1480 X-ray sources. We use a false alarm
probability analysis to estimate the contamination by interlopers, and expect ~
10 per cent of optical counterparts to be chance alignments. To determine the
most likely counterpart for each X-ray source, we compute the likelihood ratio
for all optical sources within the 4{\sigma} X-ray error circle. This analysis
yields 1480 potential counterparts (~ 90 per cent of the sample). 584
counterparts have saturated photometry (r'<17, i'<16), indicating these objects
are likely foreground sources and the real counterparts. 171 candidate
counterparts are detected only in the i'-band. These sources are good qLMXB and
CV candidates as they are X-ray bright and likely located in the Bulge.Comment: 18 pages, 18 figures. Published in MNRAS. 2016MNRAS.458.4530
Spectroscopic classification of X-ray sources in the Galactic Bulge Survey
We present the classification of 26 optical counterparts to X-ray sources
discovered in the Galactic Bulge Survey. We use (time-resolved) photometric and
spectroscopic observations to classify the X-ray sources based on their
multi-wavelength properties. We find a variety of source classes, spanning
different phases of stellar/binary evolution. We classify CX21 as a quiescent
cataclysmic variable (CV) below the period gap, and CX118 as a high accretion
rate (nova-like) CV. CXB12 displays excess UV emission, and could contain a
compact object with a giant star companion, making it a candidate symbiotic
binary or quiescent low mass X-ray binary (although other scenarios cannot be
ruled out). CXB34 is a magnetic CV (polar) that shows photometric evidence for
a change in accretion state. The magnetic classification is based on the
detection of X-ray pulsations with a period of 81 2 min. CXB42 is
identified as a young stellar object, namely a weak-lined T Tauri star
exhibiting (to date unexplained) UX Ori-like photometric variability. The
optical spectrum of CXB43 contains two (resolved) unidentified double-peaked
emission lines. No known scenario, such as an AGN or symbiotic binary, can
easily explain its characteristics. We additionally classify 20 objects as
likely active stars based on optical spectroscopy, their X-ray to optical flux
ratios and photometric variability. In 4 cases we identify the sources as
binary stars.Comment: Accepted for publication in MNRA
The Relationship Between X-ray Luminosity and Duty Cycle for Dwarf Novae and their Specific Frequency in the Inner Galaxy
We measure the duty cycles for an existing sample of well observed, nearby
dwarf novae using data from AAVSO, and present a quantitative empirical
relation between the duty cycle of dwarf novae outbursts and the X-ray
luminosity of the system in quiescence. We have found that , where
DC stands for duty cycle. We note that there is intrinsic scatter in this
relation greater than what is expected from purely statistical errors. Using
the dwarf nova X-ray luminosity functions from \citet{Pretorius12} and
\citet{Byckling10}, we compare this relation to the number of dwarf novae in
the Galactic Bulge Survey which were identified through optical outbursts
during an 8-day long monitoring campaign. We find a specific frequency of X-ray
bright () Cataclysmic Variables undergoing
Dwarf Novae outbursts in the direction of the Galactic Bulge of
. Such a specific frequency would give
a Solar neighborhood space density of long period CVs of
pc. We advocate the use of specific
frequency in future work, given that projects like LSST will detect DNe well
outside the distance range over which .Comment: 9 pagers, 4 figures Accepted for publication in MNRA
The All-Sky Automated Survey for Supernovae (ASAS-SN) Light Curve Server v1.0
The All-Sky Automated Survey for Supernovae (ASAS-SN) is working towards
imaging the entire visible sky every night to a depth of V~17 mag. The present
data covers the sky and spans ~2-5~years with ~100-400 epochs of observation.
The data should contain some ~1 million variable sources, and the ultimate goal
is to have a database of these observations publicly accessible. We describe
here a first step, a simple but unprecedented web interface
https://asas-sn.osu.edu/ that provides an up to date aperture photometry light
curve for any user-selected sky coordinate. Because the light curves are
produced in real time, this web tool is relatively slow and can only be used
for small samples of objects. However, it also imposes no selection bias on the
part of the ASAS-SN team, allowing the user to obtain a light curve for any
point on the celestial sphere. We present the tool, describe its capabilities,
limitations, and known issues, and provide a few illustrative examples.Comment: 8 pages, 9 figures, submitted to PAS
Discovery of a high state AM CVn binary in the Galactic Bulge Survey
We report on the discovery of a hydrogen-deficient compact binary (CXOGBS
J175107.6-294037) belonging to the AM CVn class in the Galactic Bulge Survey.
Deep archival X-ray observations constrain the X-ray positional uncertainty of
the source to 0.57 arcsec, and allow us to uniquely identify the optical and UV
counterpart. Optical spectroscopic observations reveal the presence of broad,
shallow He i absorption lines while no sign of hydrogen is present, consistent
with a high state system. We present the optical lightcurve from Optical
Gravitational Lensing Experiment monitoring, spanning 15 years. It shows no
evidence for outbursts; variability is present at the 0.2 mag level on
timescales ranging from hours to weeks. A modulation on a timescale of years is
also observed. A Lomb-Scargle analysis of the optical lightcurves shows two
significant periodicities at 22.90 and 23.22 min. Although the physical
interpretation is uncertain, such timescales are in line with expectations for
the orbital and superhump periods. We estimate the distance to the source to be
between 0.5 - 1.1 kpc. Spectroscopic follow-up observations are required to
establish the orbital period, and to determine whether this source can serve as
a verification binary for the eLISA gravitational wave mission.Comment: Accepted for publication in MNRAS Letter
3D-Laser-Scanning Technique Applied to Bulk Density Measurements of Apollo Lunar Samples
In order to better interpret gravimetric data from orbiters such as GRAIL and LRO to understand the subsurface composition and structure of the lunar crust, it is import to have a reliable database of the density and porosity of lunar materials. To this end, we have been surveying these physical properties in both lunar meteorites and Apollo lunar samples. To measure porosity, both grain density and bulk density are required. For bulk density, our group has historically utilized sub-mm bead immersion techniques extensively, though several factors have made this technique problematic for our work with Apollo samples. Samples allocated for measurement are often smaller than optimal for the technique, leading to large error bars. Also, for some samples we were required to use pure alumina beads instead of our usual glass beads. The alumina beads were subject to undesirable static effects, producing unreliable results. Other investigators have tested the use of 3d laser scanners on meteorites for measuring bulk volumes. Early work, though promising, was plagued with difficulties including poor response on dark or reflective surfaces, difficulty reproducing sharp edges, and large processing time for producing shape models. Due to progress in technology, however, laser scanners have improved considerably in recent years. We tested this technique on 27 lunar samples in the Apollo collection using a scanner at NASA Johnson Space Center. We found it to be reliable and more precise than beads, with the added benefit that it involves no direct contact with the sample, enabling the study of particularly friable samples for which bead immersion is not possibl
Constraining the nature of the accreting binary in CXOGBS J174623.5-310550
We report optical and infrared observations of the X-ray source CXOGBS
J174623.5-310550. This Galactic object was identified as a potential quiescent
low-mass X-ray binary accreting from an M-type donor on the basis of optical
spectroscopy and the broad Halpha emission line. The analysis of X-shooter
spectroscopy covering 3 consecutive nights supports an M2/3-type spectral
classification. Neither radial velocity variations nor rotational broadening is
detected in the photospheric lines. No periodic variability is found in I- and
r'-band light curves. We derive r' = 20.8, I = 19.2 and Ks = 16.6 for the
optical and infrared counterparts with the M-type star contributing 90% to the
I-band light. We estimate its distance to be 1.3-1.8 kpc. The lack of radial
velocity variations implies that the M-type star is not the donor star in the
X-ray binary. This could be an interloper or the outer body in a hierarchical
triple. We constrain the accreting binary to be a < 2.2 hr orbital period
eclipsing cataclysmic variable or a low-mass X-ray binary lying in the
foreground of the Galactic Bulge.Comment: (9 pages, 5 figures, accepted for publication in MNRAS
A dynamical model of surrogate reactions
A new dynamical model is developed to describe the whole process of surrogate
reactions; transfer of several nucleons at an initial stage, thermal
equilibration of residues leading to washing out of shell effects and decay of
populated compound nuclei are treated in a unified framework. Multi-dimensional
Langevin equations are employed to describe time-evolution of collective
coordinates with a time-dependent potential energy surface corresponding to
different stages of surrogate reactions. The new model is capable of
calculating spin distributions of the compound nuclei, one of the most
important quantity in the surrogate technique. Furthermore, various observables
of surrogate reactions can be calculated, e.g., energy and angular distribution
of ejectile, and mass distributions of fission fragments. These features are
important to assess validity of the proposed model itself, to understand
mechanisms of the surrogate reactions and to determine unknown parameters of
the model. It is found that spin distributions of compound nuclei produced in
O+U O+U and O+U
O+U reactions are equivalent and much less than
10, therefore satisfy conditions proposed by Chiba and Iwamoto (PRC 81,
044604(2010)) if they are used as a pair in the surrogate ratio method.Comment: 17 pages, 5 figure
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