1,221 research outputs found
The orthogonal fitting procedure for determination of the empirical {\Sigma} - D relations for supernova remnants: application to starburst galaxy M82
The radio surface brightness-to-diameter ({\Sigma} - D) relation for
supernova remnants (SNRs) in the starburst galaxy M82 is analyzed in a
statistically more robust manner than in the previous studies that mainly
discussed sample quality and related selection effects. The statistics of data
fits in log {\Sigma} - log D plane are analyzed by using vertical (standard)
and orthogonal regressions. As the parameter values of D - {\Sigma} and
{\Sigma} - D fits are invariant within the estimated uncertainties for
orthogonal regressions, slopes of the empirical {\Sigma} - D relations should
be determined by using the orthogonal regression fitting procedure. Thus
obtained {\Sigma} - D relations for samples which are not under severe
influence of the selection effects could be used for estimating SNR distances.
Using the orthogonal regression fitting procedure {\Sigma} - D slope {\beta}
\approx 3.9 is obtained for the sample of 31 SNRs in M82. The results of
implemented Monte Carlo simulations show that the sensitivity selection effect
does not significantly influence the slope of M82 relation. This relation could
be used for estimation of distances to SNRs that evolve in denser interstellar
environment, with number denisty up to 1000 particles per cm3 .Comment: 14 pages, 3 figures, no changes, previous version had a typo in
publication related comment, accepted for publication in Ap
First optical light from the supernova remnant G 17.4-2.3
Deep optical CCD images of the supernova remnant G 17.4-2.3 were obtained and
faint emission has been discovered. The images, taken in the emission lines of
Halpha+[N II], [S II] and [O III], reveal filamentary structures in the east,
south-east area, while diffuse emission in the south and central regions of the
remnant is also present. The radio emission in the same area is found to be
well correlated with the brightest optical filament. The flux calibrated images
suggest that the optical filamentary emission originates from shock-heated gas
([S II]/Halpha > 0.4), while the diffuse emission seems to originate from an
HII region ([S II]/Halpha < 0.3). Furthermore, deep long-slit spectra were
taken at the bright [O III] filament and clearly show that the emission
originates from shock heated gas. The [O III] flux suggests shock velocities
into the interstellar "clouds" greater than 100 km/s, while the [S II]
6716/6731 ratio indicates electron densities ~240 cm^{-3}. Finally, the Halpha
emission has been measured to be between 7 to 20 x 10^{-17} erg s^{-1} cm^{-2}
arcsec^{-2}.Comment: 6 pages, 5 figures, accepted for publication in A&
A Sino-German 6\ cm polarization survey of the Galactic plane VI. Discovery of supernova remnants G178.2-4.2 and G25.1-2.3
Supernova remnants (SNRs) were often discovered in radio surveys of the
Galactic plane. Because of the surface-brightness limit of previous surveys,
more faint or confused SNRs await discovery. The Sino-German 6\ cm
Galactic plane survey is a sensitive survey with the potential to detect new
low surface-brightness SNRs. We want to identify new SNRs from the 6\
cm survey map of the Galactic plane. We searched for new shell-like objects in
the 6\ cm survey maps, and studied their radio emission, polarization,
and spectra using the 6\ cm maps together with the 11\ cm and
21\ cm Effelsberg observations. Extended polarized objects with
non-thermal spectra were identified as SNRs. We have discovered two new, large,
faint SNRs, G178.2-4.2 and G25.1-2.3, both of which show shell structure.
G178.2-4.2 has a size of 72 arcmin x 62 arcmin with strongly polarized emission
being detected along its northern shell. The spectrum of G178.2-4.2 is
non-thermal, with an integrated spectral index of . Its
surface brightness is , which makes G178.2-4.2 the second faintest known Galactic SNR.
G25.1-2.3 is revealed by its strong southern shell which has a size of 80
arcmin x 30\arcmin. It has a non-thermal radio spectrum with a spectral index
of . Two new large shell-type SNRs have been detected at
6\ cm in an area of 2200 deg^2 along the the Galactic plane. This
demonstrates that more large and faint SNRs exist, but are very difficult to
detect.Comment: 8 pages, 8 figures, accepted by Astronomy and Astrophysics. For the
version with high resolution figures, please go to
http://zmtt.bao.ac.cn/6cm/papers/2newSNR.pd
Radio Observations of the Supernova Remnant Candidate G312.5-3.0
The radio images from the Parkes-MIT-NRAO (PMN) Southern Sky Survey at 4850
MHz have revealed a number of previously unknown radio sources. One such
source, G312.5-3.0 (PMN J1421-6415), has been observed using the
multi-frequency capabilities of the Australia Telescope Compact Array (ATCA) at
frequencies of 1380 MHz and 2378 MHz. Further observations of the source were
made using the Molonglo Observatory Synthesis Telescope (MOST) at a frequency
of 843 MHz. The source has an angular size of 18 arcmin and has a distinct
shell structure. We present the reduced multi-frequency observations of this
source and provide a brief argument for its possible identification as a
supernova remnant.Comment: 5 pages, 5 figures, Accepted for publication in MNRA
Information practices of disaster preparedness professionals in multidisciplinary groups
OBJECTIVE: This article summarizes the results of a descriptive qualitative study addressing the question, what are the information practices of the various professionals involved in disaster preparedness? We present key results, but focus on issues of choice and adaptation of models and theories for the study. METHODS: Primary and secondary literature on theory and models of information behavior were consulted. Taylor's Information Use Environments (IUE) model, Institutional Theory, and Dervin's Sense-Making metatheory were used in the design of an open-ended interview schedule. Twelve individual face-to-face interviews were conducted with disaster professionals drawn from the Pennsylvania Preparedness Leadership Institute (PPLI) scholars. Taylor's Information Use Environments (IUE) model served as a preliminary coding framework for the transcribed interviews. RESULTS: Disaster professionals varied in their use of libraries, peer-reviewed literature, and information management techniques, but many practices were similar across professions, including heavy Internet and email use, satisficing, and preference for sources that are socially and physically accessible. CONCLUSIONS: The IUE model provided an excellent foundation for the coding scheme, but required modification to place the workplace in the larger social context of the current information society. It is not possible to confidently attribute all work-related information practices to professional culture. Differences in information practice observed may arise from professional training and organizational environment, while many similarities observed seem to arise from everyday information practices common to non-work settings
Endogenous Transmembrane TNF-Alpha Protects Against Premature Senescence in Endothelial Colony Forming Cells
RATIONALE:
Transmembrane tumor necrosis factor-α (tmTNF-α) is the prime ligand for TNF receptor 2, which has been shown to mediate angiogenic and blood vessel repair activities in mice. We have previously reported that the angiogenic potential of highly proliferative endothelial colony-forming cells (ECFCs) can be explained by the absence of senescent cells, which in mature endothelial cells occupy >30% of the population, and that exposure to a chronic inflammatory environment induced premature, telomere-independent senescence in ECFCs.
OBJECTIVE:
The goal of this study was to determine the role of tmTNF-α in the proliferation of ECFCs.
METHODS AND RESULTS:
Here, we show that tmTNF-α expression on ECFCs selects for higher proliferative potential and when removed from the cell surface promotes ECFC senescence. Moreover, the induction of premature senescence by chronic inflammatory conditions is blocked by inhibition of tmTNF-α cleavage. Indeed, the mechanism of chronic inflammation-induced premature senescence involves an abrogation of tmTNF/TNF receptor 2 signaling. This process is mediated by activation of the tmTNF cleavage metalloprotease TNF-α-converting enzyme via p38 MAP kinase activation and its concurrent export to the cell surface by means of increased iRhom2 expression.
CONCLUSIONS:
Thus, we conclude that tmTNF-α on the surface of highly proliferative ECFCs plays an important role in the regulation of their proliferative capacity
A search for the radio counterpart of the unidentified gamma-ray source 3EG J1410-6147
We have made radio continuum, HI and X-ray observations in the direction of
the unidentified EGRET source 3EG J1410-6147, using the Australia Telescope
Compact Array and the Chandra X-ray Observatory. The observations encompass the
supernova remnant (SNR) G312.4-0.4 and the two young pulsars PSRs J1412-6145
and J1413-6141.
We derive a lower distance limit of 6 kpc to the SNR, although interpretation
of positive velocity features in the HI spectrum may imply the SNR is more
distant than 14 kpc. PSR J1412-6145, with an age of 50 kyr, is the pulsar most
likely associated with SNR G312.4-0.4. X-rays are not detected from either
pulsar and diffuse X-ray emission near the bright western edge of the SNR is
weak. Although there is circumstantial evidence that this western region is a
pulsar wind nebula (PWN), the embedded pulsar PSR J1412-6145 is apparently not
sufficiently powerful to explain the radio enhancement. The origin of the
electron acceleration in this region and of the gamma-rays remain unidentified,
unless the distance to PSR J1413-6141 is at least a factor of 3 lower than its
dispersion measure distance.Comment: 10 pages, plus 5 jpeg figures, MNRAS, in press. Full postscript or
pdf including all figures is available at http://www.ast.cam.ac.uk/~m
The theory of synchrotron emission from supernova remnants
The time-dependent nonlinear kinetic theory for cosmic ray (CR) acceleration
in supernova remnants (SNRs) is applied studying the properties of the
synchrotron emission from SNRs, in particular, the surface brightness-diameter
() relation. Detailed numerical calculations are performed for the
expected range of the relevant physical parameters, namely the ambient density
and the supernova explosion energy. The magnetic field in SNRs is assumed to be
significantly amplified by the efficiently accelerating nuclear CR component.
Due to the growing number of accelerated CRs the expected SNR luminosity
increases during the free expansion phase, reaches a peak value at the
beginning of the Sedov phase and then decreases again, since in this stage the
overall CR number remains nearly constant, whereas the effective magnetic field
diminishes with time. The theoretically predicted brightness-diameter relation
in the radio range in the Sedov phase is close to . It fits the observational data in a very satisfactory way. The
observed spread of at a given SNR size is the result of
the spread of supernova explosion energies and interstellar medium densities.Comment: 13 pages, 8 figures, accepted for publication in Astronomy &
Astrophysic
Multi-wavelength study of a new Galactic SNR G332.5-5.6
We present compelling evidence for confirmation of a Galactic supernova
remnant (SNR) candidate, G332.5-5.6, based initially on identification of new,
filamentary, optical emission line nebulosity seen in the arcsecond resolution
images from the AAO/UKST HAlpha survey. The extant radio observations and X-ray
data which we have independently re-reduced, together with new optical
spectroscopy of the large-scale fragmented nebulosity, confirms the
identification. Optical spectra, taken across five different, widely separated
nebula regions of the remnant as seen on the HAlpha images, show average ratios
of [NII]/HAlpha =2.42, [SII]/HAlpha = 2.10, and [SII] 6717/6731 = 1.23, as well
as strong [OI] 6300, 6364A and [OII] 3727A emission. These ratios are firmly
within those typical of SNRs. Here, we also present the radio-continuum
detection of the SNR at 20/13cm from observations with the Australia Telescope
Compact Array (ATCA). Radio emission is also seen at 4850 MHz, in the PMN
survey (Griffith and Wright 1993) and at 843 MHz from the SUMSS survey (Bock,
Large and Sadler 1999). We estimate an angular diameter of ~30 arcmin and
obtain an average radio spectral index of alpha = -0.6 +- 0.1 which indicates
the non-thermal nature of G332.5-5.6. Fresh analysis of existing ROSAT X-ray
data in the vicinity also confirms the existence of the SNR. The distance to
G332.5-5.6 has been independently estimated by Reynoso and Green (2007) as 3.4
kpc based on measurements of the HI lambda21 cm line seen in absorption against
the continuum emission. Our cruder estimates via assumptions on the height of
the dust layer (3.1 kpc) and using the Sigma-D relation (4 kpc) are in good
agreement.Comment: 14 pages, 18 figures. Accepted for publishing in the MNRA
Galactic neutron stars I. Space and velocity distributions in the disk and in the halo
Aims. Neutron stars (NSs) produced in the Milky Way are supposedly ten to the
eighth - ten to the ninth, of which only are observed.
Constraining the phase space distribution of NSs may help to characterize the
yet undetected population of stellar remnants. Methods. We perform Monte Carlo
simulations of NS orbits, under different assumptions concerning the Galactic
potential and the distribution of progenitors and birth velocities. We study
the resulting phase space distributions, focusing on the statistical properties
of the NS populations in the disk and in the solar neighbourhood. Results. It
is shown that percent of NSs are in bound orbits. The fraction of NSs
located in a disk of radius 20 kpc and width 0.4 kpc is percent.
Therefore the majority of NSs populate the halo. Fits for the surface density
of the disk, the distribution of heights on the Galactic plane and the velocity
distribution of the disk, are given. We also provide sky maps of the projected
number density in heliocentric Galactic coordinates (l, b). Our results are
compared with previous ones reported in the literature. Conclusions. Obvious
applications of our modelling are in the revisiting of accretion luminosities
of old isolated NSs, the issue of the observability of the nearest NS and the
NS optical depth for microlensing events. These will be the scope of further
studies.Comment: 11 pages, 15 figures, accepted for publication in Astronomy and
Astrophysic
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