100 research outputs found
The Changing Thai-United States Alliance: Implications for the Nixon Doctrine in Asia
In this article the author discusses the prospects for successful implementation of the Nixon Doctrine in Asiaâafter the withdrawal of large numbers of U.S. military forces from South Vietnamâin view of recent indicators emanating from Bangkok
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
Detection of OH absorption against PSR B1849+00
We have searched for OH absorption against seven pulsars using the Arecibo
telescope. In both OH mainlines (at 1665 and 1667 MHz), deep and narrow
absorption features were detected toward PSR B1849+00. In addition, we have
detected several absorption and emission features against B33.6+0.1, a nearby
supernova remnant (SNR). The most interesting result of this study is that a
pencil-sharp absorption sample against the PSR differs greatly from the
large-angle absorption sample observed against the SNR. If both the PSR and the
SNR probe the same molecular cloud then this finding has important implications
for absorption studies of the molecular medium, as it shows that the statistics
of absorbing OH depends on the size of the background source. We also show that
the OH absorption against the PSR most likely originates from a small (<30
arcsec) and dense (>10^5 cm^-3) molecular clump.Comment: 12 pages, 8 figures. Accepted for publication in Ap
The Galactic Distribution of Large HI Shells
We report the discovery of nineteen new HI shells in the Southern Galactic
Plane Survey (SGPS). These shells, which range in radius from 40 pc to 1 kpc,
were found in the low resolution Parkes portion of the SGPS dataset, covering
Galactic longitudes l=253 deg to l=358 deg. Here we give the properties of
individual shells, including positions, physical dimensions, energetics,
masses, and possible associations. We also examine the distribution of these
shells in the Milky Way and find that several of the shells are located between
the spiral arms of the Galaxy. We offer possible explanations for this effect,
in particular that the density gradient away from spiral arms, combined with
the many generations of sequential star formation required to create large
shells, could lead to a preferential placement of shells on the trailing edges
of spiral arms. Spiral density wave theory is used in order to derive the
magnitude of the density gradient behind spiral arms. We find that the density
gradient away from spiral arms is comparable to that out of the Galactic plane
and therefore suggest that this may lead to exaggerated shell expansion away
from spiral arms and into interarm regions.Comment: 25 pages, 20 embedded EPS figures, uses emulateapj.sty, to appear in
the Astrophysical Journa
The Southern Galactic Plane Survey: The Test Region
The Southern Galactic Plane Survey (SGPS) is a project to image the HI line
emission and 1.4 GHz continuum in the fourth quadrant of the Milky Way at high
resolution using the Australia Telescope Compact Array (ATCA) and the Parkes
Radio Telescope. In this paper we describe the survey details and goals,
present lambda 21-cm continuum data, and discuss HI absorption and emission
characteristics of the SGPS Test Region (325.5 deg < l < 333.5 deg; -0.5 deg <
b < +3.5 deg). We explore the effects of massive stars on the interstellar
medium (ISM) through a study of HI shells and the HI environments of HII
regions and supernova remnants. We find an HI shell surrounding the HII region
RCW 94 which indicates that the region is embedded in a molecular cloud. We
give lower limits for the kinematic distances to SNRs G327.4+0.4 and G330.2+1.0
of 4.3 kpc and 4.9 kpc, respectively. We find evidence of interaction with the
surrounding HI for both of these remnants. We also present images of a possible
new SNR G328.6-0.0. Additionally, we have discovered two small HI shells with
no counterparts in continuum emission.Comment: 17 pages, 7 embedded EPS figures, 10 low-res jpeg figures, uses
emulateapj5.sty. Accepted for publication in the Astrophysical Journal.
Version with all full resolution figures embedded is available at
http://www.astro.umn.edu/~naomi/sgps/papers/SGPS.ps.g
Discovery of a Candidate Central Compact Object in the Galactic Nonthermal SNR G330.2+1.0
We report on the discovery of a pointlike source (CXOU J160103.1513353) at
the center of a Galactic supernova remnant (SNR) G330.2+1.0 with {\it Chandra
X-Ray Observatory}. The X-ray spectrum fits a black-body (BB) model with
0.49 keV, implying a small emission region of 0.4 km at the
distance of 5 kpc. The estimated X-ray luminosity is 1
10 ergs s in the 1 10 keV band. A power law model may also
fit the observed spectrum, but the fit results in a very large photon index,
5. We find no counterparts at other wavelengths. The X-ray
emission was steady over the 13 hr observation period, showing no
variability. While we find marginal evidence for X-ray pulsations (
7.5 s), the presence of a pulsar at the position of this object is
not conclusive with the current data, requiring an independent confirmation.
These results are generally consistent with an interpretation of this object as
a Central Compact Object associated with SNR G330.2+1.0.Comment: 9 pages (AASTex preprint style) including 1 Table and 4 Figures.
Accepted by ApJ Letter
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