266 research outputs found
N49: the first robust discovery of a recombining plasma in an extra galactic supernova remnant
Recent discoveries of recombining plasmas (RPs) in supernova remnants (SNRs)
have dramatically changed our understanding of SNR evolution. To date, a dozen
of RP SNRs have been identified in the Galaxy. Here we present Suzaku deep
observations of four SNRs in the Large Magellanic Cloud (LMC), N49, N49B, N23,
and DEM L71, for accurate determination of their plasma state. Our uniform
analysis reveals that only N49 is in the recombining state among them, which is
the first robust discovery of a RP from an extra-galactic SNR. Given that RPs
have been identified only in core-collapse SNRs, our result strongly suggests a
massive star origin of this SNR. On the other hand, no clear evidence for a RP
is confirmed in N23, from which detection of recombination lines and continua
was previously claimed. Comparing the physical properties of the RP SNRs
identified so far, we find that all of them are categorized into the
"mixed-morphology" class and interacting with surrounding molecular clouds.
This might be a key to solve formation mechanisms of the RPs.Comment: 8 pages, 4 figures, Accepted for publication in Ap
Asymmetric Ejecta Distribution in SN 1006
We present the results from deep X-ray observations (~400 ks in total) of SN
1006 by the X-ray astronomy satellite Suzaku. The thermal spectrum from the
entire supernova remnant (SNR) exhibits prominent emission lines of O, Ne, Mg,
Si, S, Ar, Ca, and Fe. The observed abundance pattern in the ejecta components
is in good agreement with that predicted by a standard model of Type Ia
supernovae (SNe). The spatially resolved analysis reveals that the distribution
of the O-burning and incomplete Si-burning products (Si, S, and Ar) is
asymmetric, while that of the C-burning products (O, Ne, and Mg) is relatively
uniform in the SNR interior. The peak position of the former is clearly shifted
by 5' (~3.2 pc at a distance of 2.2 kpc) to the southeast from the SNR's
geometric center. Using the SNR age of ~1000 yr, we constrain the velocity
asymmetry (in projection) of ejecta to be ~3100 km/s. The abundance of Fe is
also significantly higher in the southeast region than in the northwest region.
Given that the non-uniformity is observed only among the heavier elements (Si
through Fe), we argue that SN 1006 originates from an asymmetric explosion, as
is expected from recent multi-dimensional simulations of Type Ia SNe, although
we cannot eliminate the possibility that an inhomogeneous ambient medium
induced the apparent non-uniformity. Possible evidence for the Cr K-shell line
and line broadening in the Fe K-shell emission is also found.Comment: 11 pages, 12 figures, 4 tables, formatted using emulateapj.cls.
Accepted for publication in Ap
Suzaku View of the Supernova Remnant RCW 86: X-Ray Studies of Newly-Discovered Fe-Rich Ejecta
We report on results of imaging and spectral analysis of the supernova
remnant (SNR) RCW 86 observed with Suzaku. The SNR is known to exhibit K-shell
emission of low ionized Fe, possibly originating from supernova ejecta. We
revealed the global distribution of the Fe-rich plasma in the entire remnant,
for the first time; the Fe-K emission was clearly detected from the west,
north, and south regions, in addition to the X-ray brighter shells of southwest
and northeast, where the presence of the Fe-rich ejecta has already been
reported. The spectrum of each region is well represented by a three-component
model consisting of low- and high-temperature thermal plasmas and a non-thermal
emission. The lower-temperature component, with elemental abundances of near
the solar values, likely originates from the forward shocked interstellar
medium, while the Fe-rich ejecta is described by the hotter plasma. From the
morphologies of the forward and reverse shocks in the west region, the total
ejecta mass is estimated to be 1-2M_sun for the typical explosion energy of ~ 1
x 10^{51} erg. The integrated flux of the Fe-K emission from the entire SNR
roughly corresponds to a total Fe mass of about 1M_sun. Both of these estimates
suggest a Type Ia supernova origin of this SNR. We also find possible evidence
of an Fe-rich clump located beyond the forward-shock front in the north rim,
which is reminiscent of ejecta knots observed in the Tycho and Vela SNRs.Comment: Published by PAS
A Suzaku Study of Ejecta Structure and Origin of Hard X-ray Emission in the Supernova Remnant G156.2+5.7
We report an X-ray study of the evolved Galactic supernova remnant (SNR)
G156.2+5.7 based on six pointing observations with Suzaku. The remnant's large
extent (100\arcmin in diameter) allows us to investigate its radial structure
in the northwestern and eastern directions from the apparent center. The X-ray
spectra were well fit with a two-component non-equilibrium ionization model
representing the swept-up interstellar medium (ISM) and the metal-rich ejecta.
We found prominent central concentrations of Si, S and Fe from the ejecta
component; the lighter elements of O, Ne and Mg were distributed more
uniformly. The temperature of the ISM component suggests a slow shock (610-960
km s), hence the remnant's age is estimated to be 7,000-15,000 yr,
assuming its distance to be 1.1 kpc. G156.2+5.7 has also been thought to
emit hard, non-thermal X-rays, despite being considerably older than any other
such remnant. In response to a recent discovery of a background cluster of
galaxies (2XMM J045637.2+522411), we carefully excluded its contribution, and
reexamined the origin of the hard X-ray emission. We found that the residual
hard X-ray emission is consistent with the expected level of the cosmic X-ray
background. Thus, no robust evidence for the non-thermal emission was obtained
from G156.2+5.7. These results are consistent with the picture of an evolved
SNR.Comment: 10 pages 8 figures, accepted for PAS
X-ray spectroscopy of galaxy clusters: beyond the CIE modeling
X-ray spectra of galaxy clusters are dominated by the thermal emission from
the hot intracluster medium. In some cases, besides the thermal component,
spectral models require additional components associated, e.g., with resonant
scattering and charge exchange. The latter produces mostly underluminous fine
spectral features. Detection of the extra components therefore requires high
spectral resolution. The upcoming X-ray missions will provide such high
resolution, and will allow spectroscopic diagnostics of clusters beyond the
current simple thermal modeling. A representative science case is resonant
scattering, which produces spectral distortions of the emission lines from the
dominant thermal component. Accounting for the resonant scattering is essential
for accurate abundance and gas motion measurements of the ICM. The high
resolution spectroscopy might also reveal/corroborate a number of new spectral
components, including the excitation by non-thermal electrons, the deviation
from ionization equilibrium, and charge exchange from surface of cold gas
clouds in clusters. Apart from detecting new features, future high resolution
spectroscopy will also enable a much better measurement of the thermal
component. Accurate atomic database and appropriate modeling of the thermal
spectrum are therefore needed for interpreting the data.Comment: published in Space Science Review
X-Ray Spectrum of a Peculiar Supernova Remnant G359.1-0.5
We present the Suzaku results of a supernova remnant (SNR), G359.1-0.5 in the
direction of the Galactic center region. From the SNR, we find prominent
K-shell lines of highly ionized Si and S ions, together with unusual structures
at 2.5-3.0 and 3.1-3.6 keV. No canonical SNR plasma model, in either ionization
equilibrium or under-ionization, can explain the structures. The energies and
shapes of the structures are similar to those of the radiative transitions of
free electrons to the K-shell of He-like Si and S ions (radiative recombination
continuum: RRC). The presence of the strong RRC structures indicates that the
plasma is in over-ionization. In fact, the observed spectrum is well fitted
with an over-ionized plasma model. The best-fit electron temperature of 0.29
keV is far smaller than the ionization temperature of 0.77 keV, which means
that G359.1-0.5 is in extreme condition of over-ionization. We report some
cautions on the physical parameters, and comment possible origins for the
over-ionized plasma.Comment: 7 pages, 5 figures, accepted for publication in PAS
Suzaku Observation of the RCW86 Northeastern Shell
This paper reports the Suzaku results on the northeast shell of RCW 86. With
the spatial and spectral analysis, we separated the X-rays into three distinct
components; low (kT_e~0.3keV) and high (kT_e~1.8keV) temperature plasmas and a
non-thermal component, and discovered their spatial distributions are different
from each other. The low temperature plasma is dominated at the east rim,
whereas the non-thermal emission is the brightest at the northeast rim which is
spatially connected from the east rim. The high temperature plasma, found to
contain the ~6.42keV line (K alpha of low-ionized iron), is enhanced at the
inward region with respect to the east rim and has no spatial correlation with
the non-thermal X-ray (the northeast). The Fe-Kalpha line, therefore, is not
related to the non-thermal emission but originates from Fe-rich ejecta heated
to the high temperatures by the reverse shock. Since the metal abundances of
the low temperature plasma are sub-solar, the most possible origin of this
component is interstellar medium heated by a blast wave. The non-thermal X-ray,
which has a power-law index of ~2.8, is likely to be synchrotron emission. A
possible scenario to explain these morphologies and spectra is: A fast moving
blast wave in a thin cavity of OB association collided with a dense
interstellar medium or cloud at the east region very recently. As the result,
the reverse shock in this interior decelerated, and arrived at the Fe-rich
region of the ejecta and heated it. In the northeast rim, on the other hand,
the blast wave is still moving fast, and accelerated high energy electrons to
emit synchrotron X-rays.Comment: 13 pages, 5 figures (9 figure files), accepted for publication in
PAS
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