784 research outputs found
NGC 3627: a galaxy-dwarf collision?
Group galaxies very often show distinct signs of interaction with both
companion galaxies and the intragroup medium. X-ray observations are
particularly helpful because they provide information on the temperatures and
the densities of the hot gas in galaxies and intergalactic space. This can put
important constraints on the nature and timescales of these interactions. We
use the XMM-Newton X-ray observations of NGC 3627 in the Leo Triplet galaxy
group to explain peculiar features visible in the polarized radio maps. We
analyzed soft X-ray (0.2-1 keV) emission from NGC 3627 to study the
distribution of the hot gas and its temperature in different areas of the
galaxy. Any change throughout the disk can reflect distortions visible in the
radio polarized emission. We also studied two bright point sources that are
probably tightly linked to the evolution of the galaxy. We find an increase in
the temperature of the hot gas in the area of the polarized radio ridge in the
western arm of the galaxy. In the eastern part of the disk we find two
ultra-luminous X-ray sources. We note a large hot gas temperature difference
(by a factor of 2) between the two bar ends. The polarized radio ridge in the
western arm of NGC 3627 is most likely formed by ram-pressure effects caused by
the movement of the galaxy through the intragroup medium. To explain the
distortions visible in the eastern part of the disk in polarized radio maps,
the asymmetry of the bar, and the distortion of the eastern arm, we propose a
recent collision of NGC 3627 with a dwarf companion galaxy.Comment: 8 pages, 6 figures, 5 tables. Accepted for publication in Astronomy
and Astrophysic
X-ray Phase-Resolved Spectroscopy of PSRs B0531+21, B1509-58, and B0540-69 with RXTE
The Rossi X-ray Timing Explorer ({\sl RXTE}) has made hundreds of
observations on three famous young pulsars (PSRs) B0531+21 (Crab), B1509-58,
and B0540-69. Using the archive {\sl RXTE} data, we have studied the
phase-resolved spectral properties of these pulsars in details. The variation
of the X-ray spectrum with phase of PSR B0531+21 is confirmed here much more
precisely and more details are revealed than the previous studies: the spectrum
softens from the beginning of the first pulse, turns to harden right at the
pulse peak and becomes the hardest at the bottom of the bridge, softens
gradually until the second peak, and then softens rapidly. Different from the
previous studies, we found that the spectrum of PSR B1509-58 is significantly
harder in the center of the pulse, which is also in contrast to that of PSR
B0531+21. The variation of the X-ray spectrum of PSR B0540-69 seems similar to
that of PSR B1509-58, but with a lower significance. Using the about 10 years
of data span, we also studied the real time evolution of the spectra of these
pulsars, and no significant evolution has been detected. We have discussed
about the constraints of these results on theoretical models of pulsar X-ray
emission.Comment: 42 pages, 24 figure
SN1993J VLBI (I): The Center of the Explosion and a Limit on Anisotropic Expansion
Phase-referenced VLBI observations of supernova 1993J at 24 epochs, from 50
days after shock breakout to the present, allowed us to determine the
coordinates of the explosion center relative to the quasi-stationary core of
the host galaxy M81 with an accuracy of 45 micro-arcsec, and to determine the
nominal proper motion of the geometric center of the radio shell with an
accuracy of 9micro-arcsec/yr. The uncertainties correspond to 160 AU for the
position and 160 km/s for the proper motion at the distance of the source of
3.63 Mpc. After correcting for the expected galactic proper motion of the
supernova around the core of M81 using HI rotation curves, we obtain a peculiar
proper motion of the radio shell center of only 320 +/- 160 km/s to the south,
which limits any possible one-sided expansion of the shell. We also find that
the shell is highly circular, the outer contours in fact being circular to
within 3%. Combining our proper motion values with the degree of circular
symmetry, we find that the expansion of the shockfront from the explosion
center is isotropic to within 5.5% in the plane of the sky. This is a more
fundamental result on isotropic expansion than can be derived from the
circularity of the images alone. The brightness of the radio shell, however,
varies along the ridge and systematically changes with time. The degree of
isotropy in the expansion of the shockfront contrasts with the asymmetries and
polarization found in optical spectral lines. Asymmetric density distributions
in the ejecta or more likely in the circumstellar medium, are favored to
reconcile the radio and optical results. We see no sign of any disk-like
density distribution of the circumstellar material, with the average axis ratio
of the radio shell of SN1993J being less than 1.04.Comment: 21 pages, LaTex + 5 Figures (encapulsated PostScript), Accepted for
Publication in the Astrophysical Journa
The Multi-Colored Hot Interstellar Medium of "The Antennae" Galaxies (NGC 4038/39)
We report the results of the analysis of the extended soft emission
discovered in the Chandra ACIS pointing at the merging system NGC 4038/39 (the
Antennae). We present a `multi-color' X-ray image that suggests both extensive
absorption by the dust in this system, peaking in the contact region, as well
as variations in the temperature of different emitting regions of the hot
interstellar medium (ISM). Spectral fits to multi-component thermal emission
models confirm this picture and give a first evaluation of the parameters of
the hot plasma. We compare the diffuse X-ray emission with radio continuum
(6cm), HI, CO, and H images to take a first look at the multi-phase ISM
of the Antennae galaxies. We find that the hot (X-ray) and cold (CO) gas have
comparable thermal pressures in the two nuclear regions. We also conclude that
the displacement between the peak of the diffuse X-ray emission in the north of
the galaxy system, towards the inner regions of the northern spiral arm (as
defined by H, radio continuum and HI), could result from ram pressure
of infalling HI clouds.Comment: Accepted by Ap
Lotus petal flap and vertical rectus abdominis myocutaneous flap in vulvoperineal reconstruction:a systematic review of differences in complications
Background Vulvoperineal defects resulting from surgical treatment of (pre)malignancies may result in reconstructive challenges. The vertical rectus abdominis muscle flap and, more recently, the fasciocutaneous lotus petal flap are often used for reconstruction in this area. The goal of this review is to compare the postoperative complications of application of these flaps.Methods:A comprehensive literature search of the PubMed, MEDLINE and Cochrane Library databases was performed until 6 June 2020. Search terms included the lotus petal flap, vertical rectus abdominis muscle flap and the vulvoperineal area. Articles were independently screened by two researchers according to the PRISMA-guidelines.Results:A total of 1074 citations were retrieved and reviewed, of which 55 were included for full text analysis. Following lotus petal flap reconstructions, the complication rate varied from 0.0% to 69.9%, with more complications concerning the recipient site compared with the donor site complications (26.0% versus 4.5%). Following vertical rectus abdominis muscle flap reconstructions the complication rate varied between 0.0% and 85.7% with almost twice the number of recipient site complications compared to donor site complications (37.1% versus 17.8%).Conclusions:Overall, the lotus petal flap has lower complication rates at both the donor and the recipient site compared with the vertical rectus abdominis muscle flap. When both options seem viable, the lotus petal flap procedure may be preferred on the basis of the reported lower complication rates
A damaging block-based model for the analysis of the cyclic behaviour of full-scale masonry structures
In this paper, a damaging block-based model is proposed for the numerical analysis of the cyclic behaviour of full-scale masonry structures. Solid 3D finite elements governed by a plastic-damage constitutive law in tension and compression are used to model the blocks, while a cohesive-frictional contact-based formulation is developed to simulate their cyclic interaction. The use of tests on small-scale specimens to calibrate the mechanical properties of the numerical model is presented and discussed. The tests belong to a comprehensive experimental campaign performed on calcium silicate brick masonry. The calibrated models are used to simulate in-plane and out-of-plane cyclic tests on masonry walls made of the same material, as well as a quasi-static cyclic pushover test on a full-scale terraced masonry house. The efficiency, the potentialities and the accuracy of the model here proposed are shown and discussed. The capability of explicitly representing structural details (e.g. running bonds) and any in-plane and through-thickness texture of masonry, which appears essential to study the response of masonry structures, is guaranteed by the block-based modelling approach. A good agreement between the numerical results and the experimental outcomes is observed. This allows to validate the model in the cyclic response as well as the strategy proposed for its mechanical characterization
Chemical enrichment of the complex hot ISM of the Antennae galaxies: I. Spatial and spectral analysis of the diffuse X-ray emission
We present an analysis of the properties of the hot interstellar medium (ISM)
in the merging pair of galaxies known as The Antennae (NGC 4038/39), performed
using the deep, coadded ~411 ks Chandra ACIS-S data set. These deep X-ray
observations and Chandra's high angular resolution allow us to investigate the
properties of the hot ISM with unprecedented spatial and spectral resolution.
Through a spatially resolved spectral analysis, we find a variety of
temperatures (from 0.2 to 0.7 keV) and Nh (from Galactic to 2x10^21 cm^-2).
Metal abundances for Ne, Mg, Si, and Fe vary dramatically throughout the ISM
from sub-solar values (~0.2) up to several times solar.Comment: 33 pages, 18 figures, revised version accepted by Astrophysical
Journal Supplement Serie
X-ray and Radio Timing of the Pulsar in 3C 58
We present timing data spanning 6.4 yr for the young and energetic PSR
J0205+6449, in the supernova remnant 3C 58. Data were obtained with the Rossi
X-ray Timing Explorer, the Jodrell Bank Observatory and the Green Bank
Telescope. We present phase-coherent timing analyses showing timing noise and
two spin-up glitches with fractional frequency increases of ~3.4E-7 near MJD
52555, and ~3.8E-6 between MJDs 52777 and 53062. These glitches are unusually
large if the pulsar was created in the historical supernova in 1181 as has been
suggested. For the X-ray timing we developed a new unbinned maximum-likelihood
method for determining pulse arrival times which performs significantly better
than the traditional binned techniques. In addition, we present an X-ray pulse
profile analysis of four years of RXTE data showing that the pulsar is detected
up to ~40 keV. We also present the first measurement of the phase offset
between the radio and X-ray pulse for this source, showing that the radio pulse
leads the X-ray pulse by phi=0.10+/-0.01 in phase. We compile all known
measurements of the phase offsets between radio and X-ray and radio and
gamma-ray pulses for X-ray and gamma-ray pulsars. We show that there is no
relationship between pulse period and phase offset, supported by our
measurement of the phase offset for PSR J0205+6449.Comment: 19 pages, 12 figures. Published in the Astrophysical Journal.
Includes additional data analysis and two new figure
- …