698 research outputs found
Chandra Observations of the Northeastern Rim of the Cygnus Loop
We present results from spatially resolved spectral analyses of the
northeastern (NE) rim of the Cygnus Loop supernova remnant (SNR) based on two
Chandra observations. One pointing includes northern outermost
abundance-enhanced regions discovered by recent Suzaku observations, while the
other pointing is located on regions with "normal" abundances in the NE rim of
the Cygnus Loop. The superior spatial resolving power of Chandra allows us to
reveal that the abundance-enhanced region is concentrated in an about
200"-thickness region behind the shock front. We confirm absolute metal
abundances (i.e., relative to H) as well as abundance ratios between metals are
consistent with those of the solar values within a factor of about 2. Also, we
find that the emission measure in the region gradually decreases toward the
shock front. These features are in contrast with those of the ejecta fragments
around the Vela SNR, which leads us to believe that the abundance enhancements
are not likely due to metal-rich ejecta. We suggest that the origin of the
plasma in this region is the interstellar medium (ISM). In the "normal"
abundance regions, we confirm that abundances are depleted to the solar values
by a factor of about 5 that is not expected in the ISM around the Cygnus Loop.
Introduction of non-thermal emission in our model fitting can not naturally
resolve the abundance-depletion problem. The origin of the depletion still
remains as an open question.Comment: 18 pages, 6 figure
The Plasma Structure of the Southwestern Region of the Cygnus Loop with the XMM-Newton Observatory
We observed the southwestern region of the Cygnus Loop in two pointings with
\textit{XMM-Newton}. The region observed is called the "blow-out" region that
is extended further in the south. The origin of the "blow-out" is not well
understood while it is suggested that there is another supernova remnant here
in radio observation. To investigate the detail structure of this region in
X-ray, we divided our fields of view into 33 box regions. The spectra are well
fitted by a two-component nonequilibrium ionization model. The emission measure
distributions of heavy elements decrease from the inner region to the outer
region of the Loop. Then, we also divided our fields of view into 26 annular
sectors to examine the radial plasma structure. Judging from metal abundances
obtained, it is consistent with that the X-ray emission is the Cygnus Loop
origin and we concluded that high- component (0.4 keV) originates
from the ejecta while low- component (0.2 keV) is derived from
the swept-up interstellar medium. The flux of low- component is much
less than that of high- component, suggesting the ISM component is very
thin. Also, the relative abundances in the ejecta component shows similar
values to those obtained from previous observations of the Cygnus Loop. We find
no evidence in X-ray that the nature of the "blow-out" region originated from
the extra supernova remnant. From the ejecta component, we calculated the
masses for various metals and estimated the origin of the Cygnus Loop as the
core-collapse explosion rather than the Type Ia supernova.Comment: 10 pages, 28 figures, accepted for publication in the Astrophysical
Journa
Vortical amplification of magnetic field at inward shock of supernova remnant Cassiopeia A
We present an interpretation of the time variability of the -ray flux
recently reported from a multi-epoch campaign of years observations of the
supernova remnant Cassiopeia A by {\it Chandra}. We show for the first time
quantitatively that the keV non-thermal flux increase up to
traces the growth of the magnetic field due to vortical amplification mechanism
at a reflection inward shock colliding with inner overdensities. The fast
synchrotron cooling as compared with shock-acceleration time scale
qualitatively supports the flux decrease.Comment: 5 pages, 2 figures, PRL in pres
Suzaku Spectroscopy of Vela Shrapnel B
We present the X-ray observation of Vela shrapnel B with the XIS on board the
Suzaku satellite. The shrapnel is one of several ejecta fragment-like features
protruding beyond the primary blast wave shock front of the Vela supernova
remnant. The spectrum of shrapnel B is well-represented by a single-temperature
thin-thermal plasma in a non-equilibrium ionization state. The elemental
abundances of O, Ne, and Mg are found to be significantly higher than the solar
values, supporting that shrapnel B originates from supernova ejecta. The
abundances of O, Ne, and Mg relative to Fe are enhanced above their solar
values, while that of Si relative to Fe are at their solar values. This
abundance pattern is similar to that in shrapnel D, except that the
enhancements of the lighter elements are less prominent, suggesting more
extensive mixing with the interstellar medium (ISM) in shrapnel B. The
contribution of the ISM is considered to be larger at the trailing region,
because the absolute abundances of some elements there are depleted relative to
those at the shrapnel's head.Comment: accepted for publication in ApJ, 7 pages, 5 figure
First Detection of Ar-K Line Emission from the Cygnus Loop
We observed the Cygnus Loop with XMM-Newton (9 pointings) and Suzaku (32
pointings) between 2002 and 2008. The total effective exposure time is 670.2
ks. By using all of the available data, we intended to improve a
signal-to-noise ratio of the spectrum. Accordingly, the accumulated spectra
obtained by the XIS and the EPIC show some line features around 3 keV that are
attributed to the S He and Ar He lines, respectively. Since the
Cygnus Loop is an evolved (10,000 yr) supernova remnant whose temperature
is relatively low (1 keV) compared with other young remnants, its spectrum
is generally faint above 3.0 keV, no emission lines, such as the Ar-K line have
ever been detected. The detection of the Ar-K line is the first time and we
found that its abundance is significantly higher than that of the solar value;
9.0 and 8.4 (in units of solar), estimated from
the XIS and the EPIC spectra, respectively. We conclude that the Ar-K line
originated from the ejecta of the Cygnus Loop. Follow-up X-ray observations to
tightly constrain the abundances of Ar-rich ejecta will be useful to accurately
estimate the progenitor's mass.Comment: 12 pages, 9 figures, accepted for publication in PAS
The First X-Ray Proper-Motion Measurements of the Forward Shock in the Northeastern Limb of SN 1006
We report on the first X-ray proper-motion measurements of the
nonthermally-dominated forward shock in the northeastern limb of SN 1006, based
on two Chandra observations taken in 2000 and 2008. We find that the proper
motion of the forward shock is about 0.48 arcsec/yr and does not vary around
the rim within the ~10% measurement uncertainties. The proper motion measured
is consistent with that determined by the previous radio observations. The mean
expansion index of the forward shock is calculated to be ~0.54 which matches
the value expected based on an evolutionary model of a Type Ia supernova with
either a power-law or an exponential ejecta density profile. Assuming pressure
equilibrium around the periphery from the thermally-dominated northwestern rim
to the nonthermally-dominated northeastern rim, we estimate the ambient density
to the northeast of SN 1006 to be about 0.085/cm^3.Comment: Accepted for publication in The Astrophysical Journal Letter
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