7,277 research outputs found
Radio Emission from the Composite Supernova Remnant G326.3-1.8 (MSH15-56)
High resolution radio observations of the composite supernova remnant (SNR)
G326.3-1.8 or MSH 15-56 with the Australia Telescope Compact Array show details
of both the shell and the bright plerion which is offset about 1/3 of the
distance from the center of the SNR to the shell. The shell appears to be
composed of thin filaments, typical of older shell SNRs. The central part of
the elongated plerion is composed of a bundle of parallel ridges which bulge
out at the ends and form a distinct ring structure on the northwestern end. The
magnetic field with a strength of order 45 microGauss, is directed along the
axis of the ridges but circles around the northwestern ring. This plerion is
large and bright in the radio but is not detected in x-ray or optical
wavelengths. There is, however, a faint hard x-ray feature closer to the shell
outside the plerion. Perhaps if the supernova explosion left a rapidly moving
magnetar with large energy input but initially rapid decay of both relativistic
particles and magnetic field, the observed differences with wavelength could be
explained.Comment: 15 pages, 10 figures, accepted by Ap
The ASCA Spectrum of the Vela Pulsar Jet
ROSAT observations of the Vela pulsar and its surroundings revealed a
collimated X-ray feature almost 45' in length (Markwardt & Ogelman 1995),
interpreted as the signature ``cocoon'' of a one-sided jet from the Vela
pulsar. We report on a new ASCA observation of the Vela pulsar jet at its head,
the point where the jet is believed to interact with the supernova remnant. The
head is clearly detected, and its X-ray spectrum is remarkably similar to the
surrounding supernova remnant spectrum, extending to X-ray energies of at least
7 keV. A ROSAT+ASCA spectrum can be fit by two-component emission models but
not standard one-component models. The lower energy component is thermal and
has a temperature of 0.29+/-0.03 keV (1 sigma); the higher energy component can
be fit by either a thermal component of temperature ~4 keV or a power law with
photon index ~2.0. Compared to the ROSAT-only results, the mechanical
properties of the jet and its cocoon do not change much. If the observed
spectrum is that of a hot jet cocoon, then the speed of the jet is at least 800
km s^-1, depending on the angle of inclination. The mechanical power driving
the jet is >10^36 erg s^-1, and the mass flow rate at the head is > 10^-6 M_sun
yr^-1. We conclude that the jet must be entraining material all along its
length in order to generate such a large mass flow rate. We also explore the
possibility that the cocoon emission is synchrotron radiation instead of
thermal.Comment: 12 pages, LaTeX in AAS v4.0 preprint style, two PS figures, accepted
for publication in the ApJ Letter
A high-resolution radio survey of the Vela supernova remnant
This paper presents a high-resolution radio continuum (843 MHz) survey of the
Vela supernova remnant. The contrast between the structures in the central
pulsar-powered nebula of the remnant and the synchrotron radiation shell allows
the remnant to be identified morphologically as a member of the composite
class. The data are the first of a composite remnant at spatial scales
comparable with those available for the Cygnus Loop and the Crab Nebula, and
make possible a comparison of radio, optical and soft X-ray emission from the
resolved shell filaments. The survey, made with the Molonglo Observatory
Synthesis Telescope, covers an area of 50 square degrees at a resolution of
43'' x 60'', while imaging structures on scales up to 30'.Comment: 18 pages, 7 jpg figures (version with ps figures at
http://astro.berkeley.edu/~dbock/papers/); AJ, in pres
Quantum steering ellipsoids, extremal physical states and monogamy
A Corrigendum for this article has been published in 2015 New J. Phys. 17 019501Any two-qubit state can be faithfully represented by a steering ellipsoid inside the Bloch sphere, but not every ellipsoid inside the Bloch sphere corresponds to a two-qubit state. We give necessary and sufficient conditions for when the geometric data describe a physical state and investigate maximal volume ellipsoids lying on the physical-unphysical boundary. We derive monogamy relations for steering that are strictly stronger than the Coffman-Kundu- Wootters (CKW) inequality for monogamy of concurrence. The CKW result is thus found to follow from the simple perspective of steering ellipsoid geometry. Remarkably, we can also use steering ellipsoids to derive non-trivial results in classical Euclidean geometry, extending Eulers inequality for the circumradius and inradius of a triangle.The EPSRC and the ARC Centre of Excellence grant no. CE110001027. DJ is funded by the Royal
Society. TR would like to thank the Leverhulme Trust. SJ acknowledges EPSRC grant EP/
K022512/1
IC 4406: a radio-infrared view
IC 4406 is a large (about 100'' x 30'') southern bipolar planetary nebula,
composed of two elongated lobes extending from a bright central region, where
there is evidence for the presence of a large torus of gas and dust. We show
new observations of this source performed with IRAC (Spitzer Space Telescope)
and the Australia Telescope Compact Array. The radio maps show that the flux
from the ionized gas is concentrated in the bright central region and
originates in a clumpy structure previously observed in H_alpha, while in the
infrared images filaments and clumps can be seen in the extended nebular
envelope, the central region showing toroidal emission. Modeling of the
infrared emission leads to the conclusion that several dust components are
present in the nebula.Comment: 22 pages, 7 figures, accepted for publication in The Astrophysical
Journal; v.2 has changes in both figures and content; preprint forma
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
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-principles characterisation of spectroscopic and bonding properties of cationic bismuth carbide clusters
Vibrational and electronic absorption spectra calculated at the (time-dependent) density functional theory level for the bismuth carbide clusters BinC2n+ (3≤n≤9) indicate significant differences in types of bonding that depend on cluster geometry. Analysis of the electronic charge densities of these clusters highlighted bonding trends consistent with the spectroscopic information. The combined data suggest that larger clusters (n>5) are likely to be kinetically unstable in agreement with the cluster mass distribution obtained in gas-aggregation source experiments. The spectral fingerprints of the different clusters obtained from our calculations also suggest that identification of specific BinC2n+ isomers of should be possible based on infra-red and optical absorption spectroscopy
Fluid Mechanical and Electrical Fluctuation Forces in Colloids
Fluctuations in fluid velocity and fluctuations in electric fields may both
give rise to forces acting on small particles in colloidal suspensions. Such
forces in part determine the thermodynamic stability of the colloid. At the
classical statistical thermodynamic level, the fluid velocity and electric
field contributions to the forces are comparable in magnitude. When quantum
fluctuation effects are taken into account, the electric fluctuation induced
van der Waals forces dominate those induced by purely fluid mechanical motions.
The physical principles are applied in detail for the case of colloidal
particle attraction to the walls of the suspension container and more briefly
for the case of forces between colloidal particles.Comment: ReVTeX format, one *.eps figur
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