126 research outputs found
High-Resolution X-ray Imaging Studies of Neutron Stars, Pulsar Wind Nebulae and Supernova Remnants
Supernova remnants serve as nearby laboratories relevant to many areas in
Astrophysics, from stellar and galaxy evolution to extreme astrophysics and the
formation of the heavy elements in the Universe. The Chandra X-ray mission has
enabled a giant leap forward in studying both SNRs and their compact stellar
remnants on sub-arcsecond scale. However, such high-resolution imaging studies
have been mostly limited to the nearby and/or relatively bright objects. There
is no question that we are missing a large population, especially in external
galaxies. Within our own Galaxy, we are presented with new fundamental
questions related to neutron stars' diversity, kicks, relativistic winds and
the way these objects interact with, and impact, their host environments. In
this white paper, we highlight some of the breakthroughs to be achieved with
future X-ray missions (such as the proposed AXIS probe) equipped with
sub-arcsecond imaging resolution and an order of magnitude improvement in
sensitivity.Comment: Astro2020 Science White Paper. 9 pages, 2 figure
Deciphering the Nature of the Pulsar Wind Nebula CTB 87 with XMM-Newton
CTB 87 (G74.9+1.2) is an evolved supernova remnant (SNR) which hosts a
peculiar pulsar wind nebula (PWN). The X-ray peak is offset from that observed
in radio and lies towards the edge of the radio nebula. The putative pulsar,
CXOU~J201609.2+371110, was first resolved with \textit{Chandra} and is
surrounded by a compact and a more extended X-ray nebula. Here we use a deep
{\textit{XMM-Newton}} observation to examine the morphology and evolutionary
stage of the PWN and to search for thermal emission expected from a supernova
shell or reverse shock interaction with supernova ejecta. We do not find
evidence of thermal X-ray emission from the SNR and place an upper limit on the
electron density of 0.05~cm for a plasma temperature keV.
The morphology and spectral properties are consistent with a 20~kyr-old
relic PWN expanding into a stellar wind-blown bubble. We also present the first
X-ray spectral index map from the PWN and show that we can reproduce its
morphology by means of 2D axisymmetric relativistic hydrodynamical simulations.Comment: 9 pages, 10 figures. Accepted for publication in MNRA
An X-ray Proper Motion Study of the LMC SNR 0509-67.5
We present a third epoch of Chandra observations of the Type Ia Large
Magellanic Cloud Supernova remnant (SNR) 0509-67.5. With these new observations
from 2020, the baseline for proper motion measurements of the expansion has
grown to 20 years (from the earliest Chandra observations in 2000). We report
here the results of these new expansion measurements. The lack of nearby bright
point sources renders absolute image alignment difficult. However, we are able
to measure the average expansion of the diameter of the remnant along several
projection directions. We find that the remnant is expanding with an average
velocity of 6120 (4900 -- 7360) km s. This high shock velocity is
consistent with previous works, and also consistent with the inference that
0509-67.5 is expanding into a very low density surrounding medium. At the
distance of the LMC, this velocity corresponds to an undecelerated age of 600
yrs, with the real age somewhat smaller.Comment: 9 pages, 5 figures. Accepted for publication in Ap
A New Method to Search for High-redshift Clusters Using Photometric Redshifts
We describe a new method (Poisson probability method, PPM) to search for high-redshift galaxy clusters and groups by using photometric redshift information and galaxy number counts. The method relies on Poisson statistics and is primarily introduced to search for megaparsec-scale environments around a specific beacon. The PPM is tailored to both the properties of the FR I radio galaxies in the Chiaberge et al. sample, which are selected within the COSMOS survey, and to the specific data set used. We test the efficiency of our method of searching for cluster candidates against simulations. Two different approaches are adopted. (1) We use two z ~ 1 X-ray detected cluster candidates found in the COSMOS survey and we shift them to higher redshift up to z = 2. We find that the PPM detects the cluster candidates up to z = 1.5, and it correctly estimates both the redshift and size of the two clusters. (2) We simulate spherically symmetric clusters of different size and richness, and we locate them at different redshifts (i.e., z = 1.0, 1.5, and 2.0) in the COSMOS field. We find that the PPM detects the simulated clusters within the considered redshift range with a statistical 1\u3c3 redshift accuracy of ~0.05. The PPM is an efficient alternative method for high-redshift cluster searches that may also be applied to both present and future wide field surveys such as SDSS Stripe 82, LSST, and Euclid. Accurate photometric redshifts and a survey depth similar or better than that of COSMOS (e.g., I < 25) are required
Should Employers Invest in Employability? Examining Employability as a Mediator in the HRM – Commitment Relationship
This study investigates the relationship between perceived investments in Human Resource (HR) practices and workplace commitment, from the perspective of social exchange theory. An innovative feature is that we introduce perceived employability as a potential mediator, thus bringing in a career perspective: our argument is that perceived investments in HR practices promote feelings of employability, which then create workplace commitment. Based on a 6-week follow-up sample (N = 437) and a 1-year follow-up sample (N = 127), the results of structural equation modeling analyses mostly provided support for our hypotheses. Participation and communication practices were linked to commitment via employability (in both samples), and training and development only in the short term (6-week sample). Performance feedback and reward practices, however, were unrelated to commitment via employability. Overall, our findings show that employees bring in career considerations, employability concerns in particular, in the exchange with their employer. In addition, we contribute to filling the HRM “black box” by showing that employability might be an explanatory mechanism in the HR practices – outcome relationship
Groin wound infection after vascular exposure ( GIVE ) multicentre cohort study
Surgical site infections (SSIs) of groin wounds are a common and potentially preventable cause of morbidity, mortality, and healthcare costs in vascular surgery. Our aim was to define the contemporaneous rate of groin SSIs, determine clinical sequelae, and identify risk factors for SSI.
An international multicentre prospective observational cohort study of consecutive patients undergoing groin incision for femoral vessel access in vascular surgery was undertaken over 3 months, follow‐up was 90 days. The primary outcome was the incidence of groin wound SSI.
1337 groin incisions (1039 patients) from 37 centres were included. 115 groin incisions (8.6%) developed SSI, of which 62 (4.6%) were superficial. Patients who developed an SSI had a significantly longer length of hospital stay (6 versus 5 days, P = .005), a significantly higher rate of post‐operative acute kidney injury (19.6% versus 11.7%, P = .018), with no significant difference in 90‐day mortality. Female sex, Body mass index≥30 kg/m2, ischaemic heart disease, aqueous betadine skin preparation, bypass/patch use (vein, xenograft, or prosthetic), and increased operative time were independent predictors of SSI.
Groin infections, which are clinically apparent to the treating vascular unit, are frequent and their development carries significant clinical sequelae. Risk factors include modifiable and non‐modifiable variables
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