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

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

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

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

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$\alpha$, O Ly$\alpha$, O Ly$\beta$, Fe XVII, Fe XVIII, Ne He$\alpha$ and Ne Ly$\alpha$ 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 $kT \sim 0.6$ keV and $2.7$ keV. The elemental abundances are obtained to be N $=$ $2.36_{-0.80}^{+0.88}$, O $=$ $0.20 \pm{0.05}$, Ne $=$ $0.47 \pm{0.12}$, Fe $=$ $0.15_{-0.02}^{+0.01}$ 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$_\odot$. Together with other peculiar properties of SN 1978K, i.e., a low expansion velocity of 500-1000 km s$^{-1}$ 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 ($\sim$10 M$_\odot$) or high-mass ($\sim$20-25 M$_\odot$) red supergiant star. However, these scenarios can not naturally explain the high mass-loss rate of the order of $\dot{M} \sim 10^{-3} \rm{M_{\odot}\ yr^{-1}}$ over $\gtrsim$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

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