Two-component Non-equilibrium Ionization Model Research Articles

A Chandra X-ray study of the mixed-morphology supernova remnant 3C 400.2

We present an analysis of archival Chandra observations of the mixed-morphology remnant 3C 400.2. We analysed spectra of different parts of the remnant to observe if the plasma properties provide hints on the origin of the mixed-morphology class. These remnants often show overionization, which is a sign of rapid cooling of the thermal plasma, and supersolar abundances of elements which is a sign of ejecta emission. Our analysis shows that the thermal emission of 3C 400.2 can be well explained by a two-component non-equilibrium ionization model, of which one component is underionized, has a high temperature (kT ≈ 3.9 keV) and supersolar abundances, while the other component has a much lower temperature (kT ≈ 0.14 keV), solar abundances and shows signs of overionization. The temperature structure, abundance values and density contrast between the different model components suggest that the hot component comes from ejecta plasma, while the cooler component has an interstellar matter origin. This provides the first evidence of an overionized plasma found in the outer regions of a supernova remnant, whereas the ejecta component of the inner region is underionized. In addition, the non-equilibrium ionization plasma component associated with the ejecta is confined to the central, brighter parts of the remnant, whereas the cooler component is present mostly in the outer regions. Therefore, our data can most naturally be explained by an evolutionary scenario in which the outer parts of the remnant are cooling rapidly due to having swept-up high-density ambient medium, while the inner parts are very hot and cooling inefficiently due to low density of the plasma. This is also known as the relic X-ray scenario.

A Suzaku Study of Ejecta Structure and Origin of Hard X-Ray Emission in the Supernova Remnant G 156.2+5.7

Abstract We report on an X-ray study of the evolved Galactic supernova remnant (SNR) G 156.2$+$5.7 based on six pointing observations with Suzaku. The remnant’s large extent (100$'$ 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 ($\sim $610–960 km s$^{-1}$); hence, the remnant’s age is estimated to be $\sim $7000–15000 yr, assuming its distance to be $\sim $1.1 kpc. G 156.2$+$5.7 has also been thought to emit hard, non-thermal X-rays, despite being considerably older than any other such remnant. In response to a recent discovery of a background cluster of galaxies (2XMM J045637.2$+$522411), we carefully excluded its contribution, and reexamined the origin of the hard X-ray emission. We found that the residual hard X-ray emission is consistent with the expected level of the cosmic X-ray background. Thus, no robust evidence for non-thermal emission was obtained from G 156.2$+$5.7. These results are consistent with the picture of an evolved SNR.

The Plasma Structure of the Southwestern Region of the Cygnus Loop with theXMM‐Newton Observatory

We observed the southwestern region of the Cygnus Loop in two pointings with XMM-Newton. The region observed is called the blow-out region, which is extended further in the south. The origin of the blow out is not well understood, but it is suggested that there is another supernova remnant here in radio observation. To investigate in detail the 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 the metal abundances obtained, it is consistent that the X-ray emission is of Cygnus Loop origin, and we conclude that the high-kTe component (~0.4 keV) originates from the ejecta, while the low-kTe component (~0.2 keV) is derived from the swept-up interstellar medium. The flux of the low-kTe component is much less than that of high-kTe component, suggesting that the ISM component is very thin. Also, the relative abundances in the ejecta component show values similar 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 a core-collapse explosion rather than a Type Ia supernova.

Evidence for Resonance Line Scattering in the Suzaku X-Ray Spectrum of the Cygnus Loop

Abstract We present an analysis of the Suzaku observation of the northeastern rim of the Cygnus Loop supernova remnant. The high detection efficiency together with the high spectral resolution of the Suzaku X-ray CCD camera enables us to detect highly-ionized C and N emission lines from the Cygnus Loop. Given the significant plasma structure within the Suzaku field of view, we selected the softest region based on ROSAT observations. The Suzaku spectral data are well characterized by a two-component non-equilibrium ionization model with different best-fit values for both the electron temperature and ionization timescale. Abundances of C to Fe are all depleted to typically 0.23 times solar with the exception of O. The abundance of O is relatively depleted by an additional factor of two compared with other heavy elements. We found that the resonance-line-scattering optical depth for the intense resonance lines of O is significant and, whereas the optical depth for other resonance lines is not as significant, it still needs to be taken into account for accurate abundance determination.

Asymmetric Ejecta Distribution of the Cygnus Loop Revealed with Suzaku

Abstract 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-$kT_\mathrm{e}$ component must be the ejecta component, while the low-$kT_\mathrm{e}$ 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 $\sim$2. The degree of ejecta-asymmetry is consistent with that expected by recent supernova explosion models.

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 and the south path, and studied the X-ray spectra along the two. The spectra can be well fitted either by a one-component nonequilibrium 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 subsolar (0.1-0.2 Z☉). The major part of the paths requires a two-component model. Because of projection effects, we conclude that the low-kTe (~0.2 keV) component surrounds the high-kTe (~0.6 keV) component, with the latter having relatively high metal abundances (~5 times solar). Since the Cygnus Loop is thought to have originated in a cavity explosion, the low-kTe component thus 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 paths. We find it to be very thin in the southwest region, suggesting a blowout along our line of sight. The metal distribution inside the ejecta exhibits nonuniformity, 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 that the progenitor mass was about 15 M☉.

Detection of Highly-Ionized Carbon and Nitrogen Emission Lines from the Cygnus Loop Supernova Remnant with the Suzaku Observatory

Abstract We present the results of a Suzaku observation at the northeastern limb of the Cygnus Loop supernova remnant. The high detection efficiency together with the high spectral resolution of the Suzaku X-ray CCD cameras enables us to detect highly-ionized C and N emission lines from the Cygnus Loop for the first time. We performed an annular spectral analysis to our data set and investigated the plasma structure along the radial direction. Our data are well characterized by a two-component non-equilibrium ionization model with different values of electron temperature. Abundances of C to Fe are all depleted to typically 0.1 solar, even for Ne. Relative abundances to O are roughly consistent with solar values.

An Analysis of the X‐Ray Emission from the Supernova Remnant 3C 397

The ASCA SIS and ROSAT PSPC spectral data of the supernova remnant 3C 397 are analyzed with a two-component nonequilibrium ionization model. In addition, the ASCA SIS0 and SIS1 spectra are fitted simultaneously in an equilibrium case. The resulting values of the hydrogen column density yield a distance of ~8 kpc to 3C 397. It is found that the hard X-ray emission, containing S and Fe Kα lines, arises primarily from the hot component, while most of the soft emission, composed mainly of Mg, Si, and Fe L lines and continuum, is produced by the cool component. The emission measures suggest that the remnant evolves in a cloudy medium and imply that the supernova progenitor might not be a massive early-type star. The cool component is approaching ionization equilibrium. The ages estimated from the ionization parameters and dynamics are all much greater than the previous determination. We restore the X-ray maps using the ASCA SIS data and compare them with the ROSAT HRI and the NRAO VLA Sky Survey 20 cm maps. The morphology with two bright concentrations suggests a bipolar remnant encountering a denser medium in the west.