1,735 research outputs found
A Comparison of X-ray and Radio Emission from the Supernova Remnant Cassiopeia A
We compare the radio and soft X-ray brightness as a function of position
within the young supernova remnant Cassiopeia A. A moderately strong
correlation (r = 0.7) was found between the X-ray emission (corrected for
interstellar absorption) and radio emission, showing that the thermal and
relativistic plasmas occupy the same volumes and are regulated by common
underlying parameters. The logarithmic slope of the relationship, ln(Sx-ray) =
1.2 x Sradio + ln(k) implies that the variations in brightness are primarily
due to path length differences. The X-ray and radio emissivities are both high
in the same general locations, but their more detailed relationship is poorly
constrained and probably shows significant scatter. The strongest radio and
X-ray absorption is found at the western boundary of Cas A. Based on the
properties of Cas A and the absorbing molecular cloud, we argue that they are
physically interacting. We also compare ASCA derived column densities with 21
cm H I and 18 cm OH optical depths in the direction of Cas A, in order to
provide an independent estimate of ISM properties. We derive an average value
for the H I spin temperature of about 40 K and measure the ratio of OH to
molecular hydrogen to be nominally larger than previous estimates.
Keywords: Cas A, Cassiopeia A, interstellar medium, molecular clouds, radio
astronomy, supernova remnants, X-ray astronomyComment: To appear in Vol. 446 of The Astrophysical Journal on Aug. 1, 1996;
10 pages with 5 embedded figures; replaced because of updated reference
The new 8th edition of TNM staging and its implications for skin cancer:a review by the British Association of Dermatologists and the Royal College of Pathologists, U.K.
Signals to their parliaments? Governmentsâ use of votes and policy statements in the EU Council
Does parliamentary oversight of governmentsâ decisions in the international arena matter? This article finds that it does: governments with strong parliamentary oversight behave differently when negotiating policies at the EU level compared with governments with less powerful parliaments. Where parliaments have formal powers to oversee and restrict their government's positions we see a significantly higher use of opposing votes and formal policy statements by those governments. This behaviour intensifies depending on the governments' standing visâĂ âvis other political parties at home. When governments are under pressure in their national parliaments they are more likely to go on record and take a stand against the majority in Brussels. These results make it clear that in EU legislative politics, governments not only consider their policy priorities and negotiation tactics with their European counterparts, but also make use of EU decision records to send signals to domestic audiences, including their national parliaments
Spatially resolved spectroscopy of Cassiopeia A with MECS on board BeppoSAX
We have performed the first detailed spatially resolved spectroscopy of Cas A
in the 1.6-10 keV energy range, using data taken with the MECS spectrometer on
board the BeppoSAX Observatory. We performed a spatial deconvolution of the
data and eventually generated a set of spectra, covering a region of about 3
arcmin radius around the centre of Cas A. The results obtained by fitting these
spectra using a non-equilibrium ionisation plasma model and a power law, are:
(i) a single thermal component is sufficient to fit all the spectra; (ii) kT is
rather uniformly distributed with a minimum in the east and a maximum in the
west, and no evidence is found for high kT expected from the interaction of the
main shock with the ISM; (iii) from the distribution of the values of the
ionisation parameter n_et we infer the presence of two distinct components: the
first (a) in the range 1-10 cm^(-3), the second (b) with values ten times
higher; if we associate component a to the CSM and component b to the ejecta,
the mass ratio M(a)/M(b)<= 1/10 indicates a progenitor star that lost only a
small fraction of the envelope during its pre-SN life. In this hypothesis the
distribution of component b across the remnant suggests that the explosion was
not spherically symmetric; (iv) the distribution of abundances indicates that
we are detecting a CSM component with almost solar composition, and an ejecta
component enriched in heavier elements. Abundances found for alpha-elements are
consistent with the current view that Cas A was produced by the explosion of a
massive star.Comment: 16 pages, 9 PostScript figures, 4 tables, Accepted for publication on
Astronomy & Astrophysics (submitted July 12, 2000; accepted December 20,
2000
A Broadband X-Ray Study of the Supernova Remnant 3C 397
We present an X-ray study of the radio bright supernova remnant (SNR) 3C 397
with ROSAT, ASCA, and RXTE. A central X-ray spot seen with the ROSAT
High-Resolution Imager hints at the presence of a pulsar-powered component, and
gives this SNR a composite X-ray morphology. Combined ROSAT and ASCA imaging
show that the remnant is highly asymmetric, with its hard X-ray emission
peaking at the western lobe. The spectrum of 3C 397 is heavily absorbed, and
dominated by thermal emission with emission lines evident from Mg, Si, S, Ar
and Fe. Single-component models fail to describe the spectrum, and at least two
components are required. We use a set of non-equilibrium ionization (NEI)
models (Borkowski et al. in preparation). The temperatures from the soft and
hard components are 0.2 keV and 1.6 keV respectively. The corresponding
ionization time-scales ( being the pre-shock hydrogen density) are
6 cm s and 6 10 cm s,
respectively. The spectrum obtained with the Proportional Counter Array (PCA)
of RXTE is contaminated by emission from the Galactic ridge, with only
15% of the count rate originating from 3C 397 in the 5-15 keV range. The PCA
spectrum allowed us to confirm the thermal nature of the hard X-ray emission. A
third component originating from a pulsar-driven component is possible, but the
contamination of the source signal by the Galactic ridge did not allow us to
find pulsations from any hidden pulsar. We discuss the X-ray spectrum in the
light of two scenarios: a young ejecta-dominated remnant of a core-collapse SN,
and a middle-aged SNR expanding in a dense ISM. Spatially resolved spectroscopy
(with CHANDRA and XMM) is needed to differentiate between the two scenarios,
and address the nature of the mysterious radio-quiet X-ray hot spot.Comment: 21 pages including 8 figures and 5 tables. Accepted for publication
in the Astrophysical journa
Expert advice and political choice in constructing European banking union
International actors promoted the transfer of regulatory authority and financial resources from national governments to the European Union (EU) in the context of establishing the prerequisites for financial stability in Europe through banking union. It was supplied, however, by a political process that kept significant resources in resolution and deposit insurance largely in national hands. This article examines the politics behind those decisions, and how the hybrid of European and national competences affects bank regulation and financial stability in the EU. It concludes that the tension between strong EU supervisory powers and weak capacity to deal with insolvent institutions will persist
Recycling bins, garbage cans or think tanks? Three myths regarding policy analysis institutes
The phrase 'think tank' has become ubiquitous â overworked and underspecified â in the political lexicon. It is entrenched in scholarly discussions of public policy as well as in the 'policy wonk' of journalists, lobbyists and spin-doctors. This does not mean that there is an agreed definition of think tank or consensual understanding of their roles and functions. Nevertheless, the majority of organizations with this label undertake policy research of some kind. The idea of think tanks as a research communication 'bridge' presupposes that there are discernible boundaries between (social) science and policy. This paper will investigate some of these boundaries. The frontiers are not only organizational and legal; they also exist in how the 'public interest' is conceived by these bodies and their financiers. Moreover, the social interactions and exchanges involved in 'bridging', themselves muddy the conception of 'boundary', allowing for analysis to go beyond the dualism imposed in seeing science on one side of the bridge, and the state on the other, to address the complex relations between experts and public policy
PROMPT: Panchromatic Robotic Optical Monitoring and Polarimetry Telescopes
Funded by $1.2M in grants and donations, we are now building
PROMPT at CTIO. When completed in late 2005, PROMPT will consist of six 0.41-meter diameter Ritchey-Chrétien telescopes on rapidly slewing mounts that respond to GRB alerts within seconds, when the afterglow is potentially extremely bright. Each mirror and camera coating is being optimized for a different wavelength range and function, including a NIR imager, two red-optimized imagers, a
blue-optimized imager, an UV-optimized imager, and an optical polarimeter. PROMPT will be able to identify
high-redshift events by dropout and distinguish these events from the similar signatures of extinction. In this way, PROMPT will act as a distance-finder scope for spectroscopic follow up on the larger 4.1-meter diameter SOAR telescope, which is also located at CTIO. When not chasing GRBs, PROMPT serves broader educational objectives across the state of North Carolina. Enclosure construction
and the first two telescopes are now complete and functioning: PROMPT observed Swiftâs first GRB in December 2004. We upgrade from two to four telescope in February 2005 and from four to six telescopes in mid-2005
Opposition and dissidence: two modes of resistance against international rule
Rule is commonly conceptualized with reference to the compliance it invokes. In this article, we propose a conception of rule via the practice of resistance instead. In contrast to liberal approaches, we stress the possibility of illegitimate rule, and, as opposed to critical approaches, the possibility of legitimate authority. In the international realm, forms of rule and the changes they undergo can thus be reconstructed in terms of the resistance they provoke. To this end, we distinguish between two types of resistance - opposition and dissidence - in order to demonstrate how resistance and rule imply each other. We draw on two case studies of resistance in and to international institutions to illustrate the relationship between rule and resistance and close with a discussion of the normative implications of such a conceptualization
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