6,072 research outputs found
Young Supernova Remnants in the Magellanic Clouds
There are a half-dozen or so young supernova remnants in the Magellanic
Clouds that display one or more of the following characteristics: high velocity
(>1000 km/s) emission, enhanced metallicity, or a rapidly rotating pulsar. I
summarize the current state of knowledge of these remnants and present some
recent results mostly from the new X-ray astronomy satellites.Comment: 10 pages, including 8 postscript figs, LaTeX. To appear in the
Proceedings of the 11th Annual October Maryland Astrophysics Conference
``Young Supernova Remnants'
Evidence for Resonance Line Scattering in the Suzaku X-ray Spectrum of the Cygnus Loop
We present an analysis of the Suzaku observation of the northeastern rim of
the Cygnus Loop supernova remnant. The high detection efficiency together with
the high spectral resolution of the Suzaku X-ray CCD camera enables us to
detect highly-ionized C and N emission lines from the Cygnus Loop. Given the
significant plasma structure within the Suzaku field of view, we selected the
softest region based on ROSAT observations. The Suzaku spectral data are well
characterized by a two-component non-equilibrium ionization model with
different best-fit values for both the electron temperature and ionization
timescale. Abundances of C to Fe are all depleted to typically 0.23 times solar
with the exception of O. The abundance of O is relatively depleted by an
additional factor of two compared with other heavy elements. We found that the
resonance-line-scattering optical depth for the intense resonance lines of O is
significant and, whereas the optical depth for other resonance lines is not as
significant, it still needs to be taken into account for accurate abundance
determination.Comment: 10 pages, 5 figures. accepted for Publications of the Astronomical
Society of Japa
On the Radio Polarization Signature of Efficient and Inefficient Particle Acceleration in Supernova Remnant SN 1006
We present a radio polarization study of SN 1006, based on combined VLA and
ATCA observations at 20 cm that resulted in sensitive images with an angular
resolution of 10 arcsec. The fractional polarization in the two bright radio
and X-ray lobes of the SNR is measured to be 0.17, while in the southeastern
sector, where the radio and non-thermal X-ray emission are much weaker, the
polarization fraction reaches a value of 0.6 +- 0.2, close to the theoretical
limit of 0.7. We interpret this result as evidence of a disordered, turbulent
magnetic field in the lobes, where particle acceleration is believed to be
efficient, and a highly ordered field in the southeast, where the acceleration
efficiency has been shown to be very low. Utilizing the frequency coverage of
our observations, an average rotation measure of ~12 rad/m2 is determined from
the combined data set, which is then used to obtain the intrinsic direction of
the magnetic field vectors. While the orientation of magnetic field vectors
across the SNR shell appear radial, a large fraction of the magnetic vectors
lie parallel to the Galactic Plane. Along the highly polarized southeastern
rim, the field is aligned tangent to the shock, and therefore also nearly
parallel to the Galactic Plane. These results strongly suggest that the ambient
field surrounding SN 1006 is aligned with this direction (i.e., from northeast
to southwest) and that the bright lobes are due to a polar cap geometry. Our
study establishes that the most efficient particle acceleration and generation
of magnetic turbulence in SN 1006 is attained for shocks in which the magnetic
field direction and shock normal are quasi-parallel, while inefficient
acceleration and little to no generation of magnetic turbulence obtains for the
quasi-perpendicular case.Comment: Accepted for publication in Astronomical Journa
ASCA Observations of the Twin Supernova Remnants in the Large Magellanic Cloud, DEM L316
We report results from an ASCA X-ray study of DEM L316, an emission nebula in
the Large Magellanic Cloud (LMC) consisting of two closely-spaced supernova
remnants (SNRs). The SIS image shows separate X-ray sources located at the
positions of the two radio- and optically-emitting SNR shells, 054769.7A and
054769.7B (hereafter, shell A and B). The individual X-ray spectrum of each
shell is well described by optically-thin thermal emission, although the
characteristics of the emission differ in important details between them. Shell
A exhibits strong iron L emission, which we attribute to the presence of
iron-rich ejecta leading to the suggestion that this SNR originates from a Type
Ia SN, an explosion of a moderate mass progenitor. Shell B, on the other hand,
has a chemical composition similar to that of the interstellar medium of the
LMC and so its X-ray emission is dominated by swept-up matter. The different
spectral features strongly disfavor the hypothesis that the two shells are due
to one supernova explosion into an interconnected bubble. We could not obtain
the evidence which positively supports the collision between two SNRs.Comment: 5 pages, 1 table, 7 figures Also available at
http://www-cr.scphys.kyoto-u.ac.jp/MC
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