Metal Rich Plasma at the Center Portion of the Cygnus Loop

We observed the center portion of the Cygnus Loop supernova remnant with the ASCA observatory. The X-ray spectrum of the center portion was significantly different from that obtained at the North-East (NE) limb. The emission lines from Si and S were quite strong while those of O and the continuum emission were similar to those obtained at the NE limb. Based on the spectral analysis, Si and S emission lines originated from a high-kTe and low ionization plasma whereas O and most of the continuum emission arose from a low-kTe and high ionization plasma. We suppose that Si and S emitting gas are present at the interior of the Loop while O lines and continuum emission mainly arise from the shell region. Therefore, we subtracted the spectrum of the NE limb from that of the center. Obtained abundances of Si, S, and Fe were 4 $\pm$ 1, 6 $\pm$ 2, and ${1.3}^{+0.6}_{-0.3}$ times higher than those of the cosmic abundances, respectively, and are $\sim$40 times richer than those obtained at the NE limb. These facts strongly support that some of the crude ejecta must be left at the center portion of the Cygnus Loop. The low abundance of Fe relative to Si and S suggests a type II SN with a massive progenitor star as the origin of the Cygnus Loop.Comment: Accepted for Publications of the Astronomical Society of Japan, 40 pages, 12 Postscript figures, uses PASJ95.sty, PASJadd.sty, and psbox.st

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

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$\beta$ and Ar He$\alpha$ lines, respectively. Since the Cygnus Loop is an evolved ($\sim$10,000 yr) supernova remnant whose temperature is relatively low ($<$1 keV) compared with other young remnants, its spectrum is generally faint above 3.0 keV, no emission lines, such as the Ar-K line have ever been detected. The detection of the Ar-K line is the first time and we found that its abundance is significantly higher than that of the solar value; 9.0$^{+4.0}_{-3.8}$ and 8.4$^{+2.5}_{-2.7}$ (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

Spatially Resolved X-ray Spectroscopy of Vela Shrapnel A

We present the detailed X-ray spectroscopy of Vela shrapnel A with the XMM-Newton satellite. Vela shrapnel A is one of several protrusions identified as bullets from Vela supernova explosion. The XMM-Newton image shows that shrapnel A consists of a bright knot and a faint trailing wake. We extracted spectra from various regions, finding a prominent Si Ly$_\alpha$ emission line in all the spectra. All the spectra are well represented by the non-equilibrium ionization (NEI) model. The abundances are estimated to be O$\sim$0.3, Ne$\sim$0.9, Mg$\sim$0.8, Si$\sim$3, Fe$\sim$0.8 times their solar values. The non-solar abundance ratio between O and Si indicates that shrapnel A originates from a deep layer of a progenitor star. We found that the relative abundances between heavy elements are almost uniform in shrapnel A, which suggests that the ejecta from supernova explosion are well mixed with swept-up interstellar medium.Comment: 11 pages, 10 figures, ApJ 10 May 2006, v642 2 issu

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

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

Discovery of a Featureless X-Ray Spectrum in the Supernova Remnant Shell of G330.2+1.0

We report here on the first pointed X-ray observation of the supernova remnant (SNR) G330.2+1.0. The X-ray morphology is characterized by an extended shell. Its X-ray spectrum is well represented by a single power-law function with a photon index of $\gamma\simeq 2.8$ and interstellar absorption of $n_{\rm H}\simeq2.6\times 10^{22}$[cm$^{-2}$]. We interpret this emission as synchrotron radiation from accelerated electrons at the SNR shock, as seen in SN 1006. The surface brightness of the X-ray emission is anti-correlated with the radio emission, and the power-law spectrum is dominated at the western shell where the radio emission is weak. The co-existence of two distinct (radio bright/X-ray faint and radio faint/X-ray bright) shells in a single supernova remnant challenges our understanding of the particle acceleration and radiation mechanisms in different interstellar environments. The object may be a good target for searching TeV gamma-rays and molecular gas surrounding the blast shock. We also report on the nature of a bright point-like source (AX J1601-5143) to the south of the SNR.Comment: PASJ, in pres