251 research outputs found
Persistent and Transient Blank Field Sources
Blank field sources (BFS) are good candidates for hosting dim isolated
neutron stars (DINS). The results of a search of BFS in the ROSAT HRI images
are revised. We then focus on transient BFS, arguing that they belong to a
rather large population. The perspectives of future research on DINS are then
discussed.Comment: 3 pages, 0 figures. Paper presented at the Conference "Isolated
Neutron Stars: from the interior to the surface", London, April 2006.
Astrophysics and Space Science, in pres
The Ultraluminous X-ray Sources NGC 1313 X-1 and X-2
We present a detailed analysis of XMM archival data of two Ultraluminous
X-ray Sources (ULXs) in the nearby spiral galaxy NGC 1313: NGC 1313 X-1 and
X-2. The spectral continuum of these sources was modeled with a soft thermal
component plus a power-law. If the soft component originates from an accretion
disk, the inferred mass of the compact remnant is > 100 M_sun, making it an
Intermediate Mass Black Hole (IMBH). A detailed analysis of the residuals of
the XMM EPIC-pn spectrum shows some evidence for the presence of an Oxygen
emission line in NGC 1313 X-1. The simultaneous presence of an excess in
emission, although at a much reduced significance level, at different energies
in the X-ray spectra of NGC 1313 X-1 and X-2 is suggestive of typical emission
lines from young supernova remnants. An optical counterpart for NGC 1313 X-2
was also identified. On an ESO 3.6 m image, the Chandra error box embraces a R
\~ 23 mag stellar-like object and excludes a previously proposed optical
counterpart.Comment: 7 pages, 2 figures, to be published in Advances in Space Researc
Detection of pulsations and a spectral feature in the X-ray emission of the isolated neutron star 1RXS J214303.7+065419/RBS 1774
We report on the results of a deep XMM-Newton observation of RBS 1774, the
most recent dim isolated neutron star candidate found in the ROSAT archive
data. Spectral and timing analysis of the high-quality PN and MOS data confirm
the association of this source with an isolated neutron star. The spectrum is
thermal and blackbody-like, and there is evidence at a significance level >
4sigma that the source is an X-ray pulsar, with spin period of 9.437 s.
Spectral fitting reveils the presence of an absorption feature at ~0.7 keV, but
at this level data do not have enough resolution to allow us to discriminate
between an absorption line or an edge. We compare the newly measured properties
of RBS 1774 with those of other known dim isolated neutron stars, and discuss
possible interpretations for the absorption feature.Comment: 21 pages, 5 figures, ApJ accepte
Autonomic responses to emotional linguistic stimuli and amplitude of low-frequency fluctuations predict outcome after severe brain injury
An accurate prognosis on the outcome of brain-injured patients with disorders of consciousness (DOC) remains a significant challenge, especially in the acute stage. In this study, we applied a multiple-technique approach to provide accurate predictions on functional outcome after 6 months in 15 acute DOC patients. Electrophysiological correlates of implicit cognitive processing of verbal stimuli and data-driven voxel-wise resting-state fMRI signals, such as the fractional amplitude of low-frequency fluctuations (fALFF), were employed. Event-related electrodermal activity, an index of autonomic activation, was recorded in response to emotional words and pseudo-words at baseline (T0). On the same day, patients also underwent a resting-state fMRI scan. Six months later (T1), patients were classified as outcome-negative and outcome-positive using a standard functional outcome scale. We then revisited the baseline measures to test their predictive power for the functional outcome measured at T1. We found that only outcome-positive patients had an earlier, higher autonomic response for words compared to pseudo-words, a pattern similar to that of healthy awake controls. Furthermore, DOC patients showed reduced fALFF in the posterior cingulate cortex (PCC), a brain region that contributes to autonomic regulation and awareness. The event-related electrodermal marker of residual cognitive functioning was found to have a significant correlation with residual local neuronal activity in the PCC. We propose that a residual autonomic response to cognitively salient stimuli, together with a preserved resting-state activity in the PCC, can provide a useful prognostic index in acute DOC
1RXS J214303.7+065419/RBS 1774: A New Isolated Neutron Star Candidate
We report on the identification of a new possible Isolated Neutron Star
candidate in archival ROSAT observations. The source 1RXS J214303.7+065419,
listed in the ROSAT Bright Survey as RBS 1774, is very soft, exhibits a thermal
spectrum well fitted by a blackbody at eV and has a low column
density, . Catalogue searches revealed
no known sources in other energy bands close to the X-ray position of RBS 1774.
Follow-up optical observations with NTT showed no peculiar object within the
X-ray error circle. The absence of any plausible optical counterpart down to
results in an X-ray to optical flux ratio in excess of 1000.Comment: LaTeX (A&A style files), 5 pages, 3 figures. Accepted for publication
in Astronomy and Astrophysics Letters. Minor correction
The Brera Multi-scale Wavelet Chandra Survey. I. Serendipitous source catalogue
We present the BMW-Chandra source catalogue drawn from essentially all
Chandra ACIS-I pointed observations with an exposure time in excess of 10ks
public as of March 2003 (136 observations). Using the wavelet detection
algorithm developed by Lazzati et al. (1999) and Campana et al. (1999), which
can characterise both point-like and extended sources, we identified 21325
sources. Among them, 16758 are serendipitous, i.e. not associated with the
targets of the pointings, and do not require a non-automated analysis. This
makes our catalogue the largest compilation of Chandra sources to date. The
0.5--10 keV absorption corrected fluxes of these sources range from ~3E-16 to
9E-12 erg cm^-2 s^-1 with a median of 7E-15 erg cm^-2 s^-1. The catalogue
consists of count rates and relative errors in three energy bands (total,
0.5-7keV; soft, 0.5-2keV; and hard, 2-7keV), and source positions relative to
the highest signal-to-noise detection among the three bands. The wavelet
algorithm also provides an estimate of the extension of the source. We include
information drawn from the headers of the original files, as well, and
extracted source counts in four additional energy bands, SB1 (0.5-1keV), SB2
(1-2keV), HB1 (2-4keV), and HB2 (4-7keV). We computed the sky coverage for the
full catalogue and for a subset at high Galactic latitude (|b|> 20deg). The
complete catalogue provides a sky coverage in the soft band (0.5-2keV, S/N =3)
of ~8 deg^2 at a limiting flux of 1E-13 erg cm^-2 s^-1, and ~2 deg^2 at a
limiting flux of ~1E-15 erg cm^-2 s^-1.Comment: Accepted by A&A, Higher res. Figs 4 and 5 at
http://www.ifc.inaf.it/~romano/BMC/Docs/aapaper/9601f4.eps
http://www.ifc.inaf.it/~romano/BMC/Docs/aapaper/9601f5.eps, Catalog Web
pages: http://www.brera.inaf.it/BMC/bmc_home.html
http://www.ifc.inaf.it/~romano/BMC/bmc_home.html (Mirror
A quasar companion to the puzzling quasar SDSS J0927+2943
We report the discovery of a quasar close to SDSS J0927+2943 (z = 0.713),
which is a massive binary / recoiling black hole candidate. The companion
quasar is at a projected distance of 125 h_70^{-1} kpc and exhibits a radial
velocity difference of ~1400 km/s with respect to the known quasar. We discuss
the nature of this peculiar quasar pair and the properties of its environment.
We propose that the overall system is caught in the process of ongoing
structure formation.Comment: 4 pages, 3 figures. Accepted for publication in A&
Procalcitonin-guided antibiotic therapy: An expert consensus
Procalcitonin (PCT) is a useful biomarker of bacterial infection and its use is associated to reduced duration of antibiotic therapy in the setting of intensive care medicine. To address the need of practical guidance for the use of PCT in various clinical settings, a group of experts was invited to participate at a consensus process with the aims of defining the rationale for appropriate use of PCT and for improving the management of critically ill patients with sepsis. A group of 14 experts from anesthesiology and critical care, infectious diseases, internal medicine, pulmonology, clinical microbiology, laboratory medicine, clinical pharmacology and methodology provided expert opinion through a modified Delphi process, after a comprehensive literature review. The appropriateness of use of PCT in terms of diagnosis, prognosis and antimicrobial stewardship was assessed for different scenarios or settings such us management of infection in the emergency department, regular wards, surgical wards or in the intensive care unit. Similarly, appropriateness and timing of PCT measurement were evaluated. All the process consisted in three Delphi rounds. PCT use is appropriate in algorithms for antibiotic de-escalation and discontinuation. In this case, reproducible, high sensitive assays should be used. However, initiation or escalation of antibiotic therapy in specific scenarios, including acute respiratory infections, should not be based solely on PCT serum levels. Clinical and radiological findings, evaluation of severity of illness and of patient's characteristics should be taken into proper account in order to correctly interpret PCT results
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