538 research outputs found
The Plasma Structure of the Cygnus Loop from the Northeastern Rim to the Southwestern Rim
The Cygnus Loop was observed from the northeast to the southwest with
XMM-Newton. We divided the observed region into two parts, the north path and
the south path, and studied the X-ray spectra along two paths. The spectra can
be well fitted either by a one-component non-equilibrium ionization (NEI) model
or by a two-component NEI model. The rim regions can be well fitted by a
one-component model with relatively low \kTe whose metal abundances are
sub-solar (0.1--0.2). The major part of the paths requires a two-component
model. Due to projection effects, we concluded that the low kTe (about 0.2 keV)
component surrounds the high kTe (about 0.6 keV) component, with the latter
having relatively high metal abundances (about 5 times solar). Since the Cygnus
Loop is thought to originate in a cavity explosion, the low-kTe component
originates from the cavity wall while the high-kTe component originates from
the ejecta. The flux of the cavity wall component shows a large variation along
our path. We found it to be very thin in the south-west region, suggesting a
blowout along our line of sight. The metal distribution inside the ejecta shows
non-uniformity, depending on the element. O, Ne and Mg are relatively more
abundant in the outer region while Si, S and Fe are concentrated in the inner
region, with all metals showing strong asymmetry. This observational evidence
implies an asymmetric explosion of the progenitor star. The abundance of the
ejecta also indicates the progenitor star to be about 15 M_sun.Comment: 24 pages, 9 figures, Astrophysical Journal in pres
First Detection of X-Ray Line Emission from Type IIn Supernova 1978K with XMM-Newton's RGS
We report on robust measurements of elemental abundances of the Type IIn
supernova SN 1978K, based on the high-resolution X-ray spectrum obtained with
the Reflection Grating Spectrometer (RGS) onboard XMM-Newton. The RGS clearly
resolves a number of emission lines, including N Ly, O Ly, O
Ly, Fe XVII, Fe XVIII, Ne He and Ne Ly for the first
time from SN 1978K. The X-ray spectrum can be represented by an absorbed,
two-temperature thermal emission model, with temperatures of keV
and keV. The elemental abundances are obtained to be N
, O , Ne , Fe
times the solar values. The low metal abundances except
for N show that the X-ray emitting plasma originates from the circumstellar
medium blown by the progenitor star. The abundances of N and O are far from
CNO-equilibrium abundances expected for the surface composition of a luminous
blue variable, and resemble the H-rich envelope of less-massive stars with
masses of 10-25 M. Together with other peculiar properties of SN 1978K,
i.e., a low expansion velocity of 500-1000 km s and SN IIn-like optical
spectra, we propose that SN 1978K is a result of either an electron-capture SN
from a super asymptotic giant branch star, or a weak Fe core-collapse explosion
of a relatively low-mass (10 M) or high-mass (20-25
M) red supergiant star. However, these scenarios can not naturally
explain the high mass-loss rate of the order of over 1000 yr before the explosion, which is
inferred by this work as well as many other earlier studies. Further
theoretical studies are required to explain the high mass-loss rates at the
final evolutionary stages of massive stars.Comment: 10 pages, 6 figures, accepted for publication in PAS
The Slow X-Ray Expansion of the Northwestern Rim of the Supernova Remnant RX J0852.0-4622
The detection of radioactive decay line of 44Ti provides a unique evidence
that the gamma-ray source is a young (< 1,000 yr) supernova remnant because of
its short lifetime of about 90 yr. Only two Galactic remnants, Cassiopeia A and
RX J0852.0-4622, are hitherto reported to be the 44Ti line emitter, although
the detection from the latter has been debated. Here we report on an expansion
measurement of the northwestern rim of RX J0852.0-4622 obtained with X-ray
observations separated by 6.5 yr. The expansion rate is derived to be
0.023+/-0.006% that is about five times lower than those of young historical
remnants. Such a slow expansion suggests that RX J0852.0-4622 is not a young
remnant as has been expected. We estimate the age of 1,700-4,300 yr of this
remnant depending on its evolutionary stage. Assuming a high shock speed of
about 3000 km/sec, which is suggested by the detection of non-thermal X-ray
radiation, the distance of about 750 pc to this remnant is also derived.Comment: 12 pages, 3 figures, Accepted for publication in the Astrophysical
Journal Letter
Asymmetric Ejecta Distribution of the Cygnus Loop revealed with Suzaku
We observed a linearly sliced area of the Cygnus Loop from the north-east to
the south-west with Suzaku in seven pointings. After dividing the entire fields
of view (FOV) into 119 cells, we extracted spectra from all of the cells and
performed spectral analysis for them. We then applied both one- and
two-component non-equilibrium ionization (NEI) models for all of the spectra,
finding that almost all were significantly better fitted by the two-component
NEI model rather than the one-component NEI model. Judging from the abundances,
the high-kT_e component must be the ejecta component, while the low-kT_e
component comes from the swept-up matter. Therefore, the ejecta turn out to be
distributed inside a large area (at least our FOV) of the Cygnus Loop. We
divided the entire FOV into northern and southern parts, and found that the
ejecta distributions were asymmetric to the geometric center: the ejecta of Si,
S, and Fe seem to be distributed more in the south than in the north of the
Cygnus Loop by a factor of about 2. The degree of ejecta-asymmetry is
consistent with that expected by recent supernova explosion models.Comment: 14 pages, 4 figure
Discovery of Fast-Moving X-Ray--Emitting Ejecta Knots in the Oxygen-Rich Supernova Remnant Puppis A
We report on the discovery of fast-moving X-ray--emitting ejecta knots in the
Galactic Oxygen-rich supernova remnant Puppis A from XMM-Newton observations.
We find an X-ray knotty feature positionally coincident with an O-rich
fast-moving optical filament with blue-shifted line emission located in the
northeast of Puppis A. We extract spectra from northern and southern regions of
the feature. Applying a one-component non-equilibrium ionization model for the
two spectra, we find high metal abundances relative to the solar values in both
spectra. This fact clearly shows that the feature originates from metal-rich
ejecta. In addition, we find that line emission in the two regions is
blue-shifted. The Doppler velocities derived in the two regions are different
with each other, suggesting that the knotty feature consists of two knots that
are close to each other along the line of sight. Since fast-moving O-rich
optical knots/filaments are believed to be recoiled metal-rich ejecta, expelled
to the opposite direction against the high-velocity central compact object, we
propose that the ejecta knots disclosed here are also part of the recoiled
material.Comment: 16 pages, 3 figure
Performance of the Charge Injection Capability of Suzaku XIS
A charge injection technique is applied to the X-ray CCD camera, XIS (X-ray
Imaging Spectrometer) onboard Suzaku. The charge transfer inefficiency (CTI) in
each CCD column (vertical transfer channel) is measured by the injection of
charge packets into a transfer channel and subsequent readout. This paper
reports the performances of the charge injection capability based on the ground
experiments using a radiation damaged device, and in-orbit measurements of the
XIS. The ground experiments show that charges are stably injected with the
dispersion of 91eV in FWHM in a specific column for the charges equivalent to
the X-ray energy of 5.1keV. This dispersion width is significantly smaller than
that of the X-ray events of 113eV (FWHM) at approximately the same energy. The
amount of charge loss during transfer in a specific column, which is measured
with the charge injection capability, is consistent with that measured with the
calibration source. These results indicate that the charge injection technique
can accurately measure column-dependent charge losses rather than the
calibration sources. The column-to-column CTI correction to the calibration
source spectra significantly reduces the line widths compared to those with a
column-averaged CTI correction (from 193eV to 173eV in FWHM on an average at
the time of one year after the launch). In addition, this method significantly
reduces the low energy tail in the line profile of the calibration source
spectrum.Comment: Paper contains 18 figures and 15 tables. Accepted for publication in
PAS
Abundance Inhomogeneity in the Northeastern Rim of the Cygnus Loop Revealed by Suzaku Observatory
We present the results of a spatially resolved spectral analysis from four
Suzaku observations covering the northeastern rim of the Cygnus Loop. A
two-kT_e non-ionization equilibrium (NEI) model fairly well represents our
data, which confirms the NEI condition of the plasma there. The metal
abundances are depleted relative to the solar values almost everywhere in our
field of view. We find abundance inhomogeneities across the field: the
northernmost region (Region A) has enhanced absolute abundances compared with
other regions. In addition, the relative abundances of Mg/O and Fe/O in Region
A are lower than the solar values, while those in the other regions are twice
higher than the solar values. As far as we are concerned, neither a
circumstellar medium, fragments of ejecta, nor abundance inhomogeneities of the
local interstellar medium around the Cygnus Loop can explain the relatively
enhanced abundance in Region A. This point is left as an open question for
future work.Comment: 13 pages, 6 figure
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