Fe-rich Ejecta Research Articles

Reverse Shock Revisited in Cassiopeia A with Chandra

Using data from the Chandra X-ray Observatory, we revisit the reverse shock in the supernova remnant (SNR) Cassiopeia A. Based on spectroscopy of a series of annuli in the northwest (NW) and southeast (SE), we get the radial profiles of the S/Si Kα line flux ratio and Fe Kα line centroid energy. They both show monotonic increase, confirming that the Si- and Fe-rich ejecta are heated by the reverse shock. The abrupt change of the S and Si line flux ratio is clearly observed in Cassiopeia A, leading to the determination of the reverse-shock location (∼1.′71 ± 0.′16 and ∼1.′35 ± 0.′18 in the NW and SE, with respect to the central source). By comparing the radial profiles of the S and Si line flux, we find that the reverse shock is moving outward in the frame of the observer, and the velocities are ∼3950 ± 210 km s−1 and ∼2900 ± 260 km s−1 in the NW and SE, respectively. In contrast, the velocities become ∼1150 km s−1 (NW) and ∼1300 km s−1 (SE) in the ejecta frame. Our measured reverse-shock velocities are quite consistent with those obtained from the X-ray and/or optical images. They therefore supply a cross-check of the accuracy for the two available methods for measuring the reverse-shock velocity in SNRs. Both the location and the velocity of the reverse shock show apparent asymmetry, suggesting that the asymmetric explosion of the progenitor plays a key role in the interaction between the reverse shock and the ejecta, ultimately shaping the complex features observed in SNRs.

Examining Neutrino–Matter Interactions in the Cassiopeia A Supernova

Neutrino interactions with stellar material are widely believed to be fundamental to the explosion of massive stars. However, this important process has remained difficult to confirm observationally. We propose a new method to verify it using X-ray observations of the supernova remnant Cassiopeia A. The elemental composition in its Fe-rich ejecta that could have been produced at the innermost region of the supernova, where neutrinos are expected to interact, allows us to examine the presence of neutrino interactions. Here we demonstrate that the amount of Mn produced without neutrino nucleosynthesis processes (i.e., the ν- and νp-processes) is too small to explain the Mn/Fe mass ratio we measure (0.14%–0.67%). This result supports the operation of significant neutrino interactions in the Cassiopeia A supernova. If the observed Mn/Fe mass ratio purely reflects the production at the innermost region of the supernova, this would be the first robust confirmation of neutrino–matter interactions in an individual supernova. We further show that the Mn/Fe mass ratio has the potential to constrain supernova neutrino parameters (i.e., total neutrino luminosity, neutrino temperature). Future spatially resolved, high-resolution X-ray spectroscopy will allow us to investigate the details of neutrino–supernova astrophysics through its signatures in elemental composition not only in Cassiopeia A but also in other remnants.

X-Ray Studies of the Inverted Ejecta Layers in the Southeast Area of Cassiopeia A

The central strong activities in core-collapse supernovae are expected to produce the overturning of the Fe- and Si/O-rich ejecta during the supernova explosion based on multidimensional simulations. X-ray observations of the supernova remnant Cassiopeia A have indicated that the Fe-rich ejecta lies outside the Si-rich materials in the southeastern region, which is consistent with the hypothesis on the inversion of the ejecta. We investigate the kinematic and nucleosynthetic properties of the inverted ejecta layers in detail to understand its formation process using the data taken by the Chandra X-Ray Observatory. Three-dimensional velocities of Fe- and Si/O-rich ejecta are obtained as >4500 km s−1 and ∼2000–3000 km s−1, respectively, by combining proper motion and line-of-sight velocities, indicating that the velocity of the Si/O-rich ejecta is slower than that of the Fe-rich ejecta from the early stages of the explosion. To constrain their burning regime, the Cr/Fe mass ratios are evaluated as % in the outermost Fe-rich region and % in the inner Fe/Si-rich region, suggesting that the complete Si burning layer is invertedly located to the incomplete Si burning layer. All the results support the ejecta overturning at the early stages of the remnant’s evolution or during the supernova explosion of Cassiopeia A.

ALMA CO Observations of the Mixed-morphology Supernova Remnant W49B: Efficient Production of Recombining Plasma and Hadronic Gamma Rays via Shock–Cloud Interactions

Abstract We carried out new CO(J = 2–1) observations toward the mixed-morphology supernova remnant (SNR) W49B with the Atacama Large Millimeter/submillimeter Array. We found that CO clouds at ∼10 km s−1 show a good spatial correspondence to the synchrotron radio continuum as well as to an X-ray deformed shell. The bulk mass of molecular clouds accounts for the western part of the shell, not the eastern shell, where near-infrared H2 emission is detected. The molecular clouds at ∼10 km s−1 show higher kinetic temperatures of ∼20–60 K, suggesting that modest shock heating occurred. The expanding motion of the clouds with ΔV ∼ 6 km s−1 was formed by strong winds from the progenitor system. We argue that the barrel-like structure of Fe-rich ejecta was possibly formed not only by an asymmetric explosion, but also by interactions with dense molecular clouds. We also found a negative correlation between the CO intensity and the electron temperature of recombining plasma, implying that the origin of the high-temperature recombining plasma in W49B can be understood to be the thermal conduction model. The total energy of accelerated cosmic-ray protons W p is estimated to be ∼2 × 1049 erg by adopting an averaged gas density of ∼650 ± 200 cm−3. The SNR age–W p diagram indicates that W49B shows one of the highest in situ values of W p among gamma-ray-bright SNRs.

The Post-impact Evolution of the X-Ray-emitting Gas in SNR 1987A as Viewed by XMM-Newton

Abstract Since 1996 the blast wave driven by SN 1987A has been interacting with the dense circumstellar material, which provides us with a unique opportunity to study the early evolution of a newborn supernova remnant (SNR). Based on the XMM-Newton RGS and EPIC-pn X-ray observations from 2007 to 2019, we investigated the post-impact evolution of the X-ray-emitting gas in SNR 1987A. The hot plasma is represented by two nonequilibrium ionization components with temperatures of ∼0.6 keV and ∼2.5 keV. The low-temperature plasma has a density ∼2400 cm−3, which is likely dominated by the lower-density gas inside the equatorial ring (ER). The high-temperature plasma with a density ∼550 cm−3 could be dominated by the H ii region and the high-latitude material beyond the ring. In the last few years, the emission measure of the low-temperature plasma has been decreasing, indicating that the blast wave has left the main ER. But the blast wave is still propagating into the high-latitude gas, resulting in the steady increase of the high-temperature emission measure. Meanwhile, the average abundances of N, O, Ne, and Mg are found to be declining, which may reflect the different chemical compositions between the two plasma components. We also detected Fe K lines in most of the observations, showing increasing flux and centroid energy. We interpret the Fe K lines as originating from a third hot component, which may come from the reflected shock heated gas or originate from Fe-rich ejecta clumps shocked by the reverse shock.

High-entropy ejecta plumes in Cassiopeia A from neutrino-driven convection.

Recent multi-dimensional simulations suggest that high-entropy buoyant plumes help massive stars to explode1,2. Outwardly protruding iron (Fe)-rich fingers of gas in the galactic supernova remnant3,4 Cassiopeia A seem to match this picture. Detecting the signatures of specific elements synthesized in the high-entropy nuclear burning regime (that is, α-rich freeze out) would constitute strong substantiating evidence. Here we report observations of such elements-stable titanium (Ti) and chromium (Cr)-at a confidence level greater than 5 standard deviations in the shocked high-velocity Fe-rich ejecta of Cassiopeia A. We found that the observed Ti/Fe and Cr/Fe mass ratios require α-rich freeze out, providing evidence of the existence of the high-entropy ejecta plumes that boosted the shock wave at explosion. The metal composition of the plumes agrees well with predictions for strongly neutrino-processed proton-rich ejecta2,5,6. These results support the operation of the convective supernova engine via neutrino heating in the supernova that produced Cassiopeia A.

Discovery of Double-ring Structure in the Supernova Remnant N103B: Evidence for Bipolar Winds from a Type Ia Supernova Progenitor

Abstract The geometric structure of supernova remnants (SNR) provides a clue to unveiling the pre-explosion evolution of their progenitors. Here we present an X-ray study of N103B (0509–68.7), a Type Ia SNR in the Large Magellanic Cloud, that is known to be interacting with dense circumstellar matter (CSM). Applying our novel method for feature extraction to deep Chandra observations, we have successfully resolved the CSM, Fe-rich ejecta, and intermediate-mass element (IME) ejecta components, and revealed each of their spatial distributions. Remarkably, the IME ejecta component exhibits a double-ring structure, implying that the SNR expands into an hourglass-shape cavity and thus forms bipolar bubbles of the ejecta. This interpretation is supported by more quantitative spectroscopy that reveals a clear bimodality in the distribution of the ionization state of the IME ejecta. These observational results can be naturally explained if the progenitor binary system had formed a dense CSM torus on the orbital plane prior to the explosion, providing further evidence that the SNR N103B originates from a single-degenerate progenitor.

The fully developed remnant of a neutrino-driven supernova

Context. The remnants of core-collapse supernovae (SNe) are probes of the physical processes associated with their parent SNe. Aims. Here we aim to explore to which extent the remnant keeps memory of the asymmetries that develop stochastically in the neutrino-heating layer due to hydrodynamic instabilities (e.g., convective overturn and the standing accretion shock instability; SASI) during the first second after core bounce. Methods. We coupled a three-dimensional (3D) hydrodynamic model of a neutrino-driven SN explosion, which has the potential to reproduce the observed morphology of the Cassiopeia A (Cas A) remnant, with 3D (magneto)-hydrodynamic simulations of the remnant formation. The simulations cover ≈2000 yr of expansion and include all physical processes relevant to describe the complexities in the SN evolution and the subsequent interaction of the stellar debris with the wind of the progenitor star. Results. The interaction of large-scale asymmetries left from the earliest phases of the explosion with the reverse shock produces, at the age of ≈350 yr, an ejecta structure and a remnant morphology which are remarkably similar to those observed in Cas A. Small-scale structures in the large-scale Fe-rich plumes that were created during the initial stages of the SN, combined with hydrodynamic instabilities that develop after the passage of the reverse shock, naturally produce a pattern of ring- and crown-like structures of shocked ejecta. The consequence is a spatial inversion of the ejecta layers with Si-rich ejecta being physically interior to Fe-rich ejecta. The full-fledged remnant shows voids and cavities in the innermost unshocked ejecta, which are physically connected with ring-like features of shocked ejecta in the main shell in most cases, resulting from the expansion of Fe-rich plumes and their inflation due to the decay of radioactive species. The asymmetric distributions of 44Ti and 56Fe, which are mostly concentrated in the northern hemisphere, and pointing opposite to the kick velocity of the neutron star, as well as their abundance ratio are both compatible with those inferred from high-energy observations of Chandra and NuSTAR. Finally, the simulations show that the fingerprints of the SN can still be visible ≈2000 yr after the explosion. Conclusions. The main asymmetries and features observed in the ejecta distribution of Cas A can be explained by the interaction of the reverse shock with the initial large-scale asymmetries that developed from stochastic processes (e.g., convective overturn and SASI activity) that originate during the first seconds of the SN blast.

A Nucleosynthetic Origin for the Southwestern Fe-rich Structure in Kepler’s Supernova Remnant

Abstract Chandra X-ray observations of Kepler’s supernova remnant indicate the existence of a high-speed Fe-rich ejecta structure in the southwestern region. We report strong K-shell emission from Fe-peak elements (Cr, Mn, Fe, Ni), as well as Ca, in this Fe-rich structure, implying that those elements could be produced in the inner area of the exploding white dwarf. We found Ca/Fe, Cr/Fe, Mn/Fe, and Ni/Fe mass ratios of 1.0%–4.1%, 1.0%–4.6%, 1%–11%, and 2%–30%, respectively. In order to constrain the burning regime that could produce this structure, we compared these observed mass ratios with those in 18 one-dimensional Type Ia nucleosynthesis models (including both near-M Ch and sub-M Ch explosion models). The observed mass ratios agree well with those around the middle layer of incomplete Si burning in Type Ia nucleosynthesis models with a peak temperature of ∼(5.0–5.3) × 109 K and a high metallicity, Z > 0.0225. Based on our results, we infer the necessity for some mechanism to produce protruding Fe-rich clumps dominated by incomplete Si-burning products during the explosion. We also discuss the future perspectives of X-ray observations of Fe-rich structures in other Type Ia supernova remnants.

Detailed X-Ray Mapping of the Shocked Ejecta and Circumstellar Medium in the Galactic Core-collapse Supernova Remnant G292.0+1.8

Abstract G292.0+1.8 (G292) is a young (∼3000 yr), Galactic textbook-type core-collapse supernova remnant. It is characterized by X-ray, optical and infrared emission from ejecta and circumstellar medium (CSM) features, and contains a pulsar (PSR J1124-5916) and pulsar wind nebula that have been observed in X-rays and radio. Previous studies have revealed a complex, dynamically evolving, oxygen-rich remnant, a striking relic from the explosion of a massive star. Here, using our deep (530 ks) Chandra ACIS data, we present high spatial-resolution maps (based on a regional grid size of a few arcsecond) of the shocked CSM and metal-rich ejecta in G292. We make the first Chandra-detection of Fe-rich ejecta in G292. We identify the X-ray counterpart of the northern equatorial belt, a component of a ring-like CSM structure identified earlier in the infrared band. We show the detailed spatial distributions of ejecta enriched in O, Ne, Mg, Si, S, and Fe. We find that the bulk of the Si, S, and Fe-rich X-ray-emitting ejecta are located in the northwestern hemisphere of the remnant, opposite to the pulsar’s projected angular displacement to the southeast from the SNR’s center. This suggests that the pulsar’s kick may have originated from gravitational and hydrodynamic forces during an asymmetric explosion, rather than from anisotropic neutrino emission. Based on abundance ratios and our estimated CSM and ejecta masses, we constrain the progenitor mass to 13 M ⊙ ≲ M ≲ 30 M ⊙

Narrow transient absorptions in late-time optical spectra of type Ia supernovae: evidence for large clumps of iron-rich ejecta?

An examination of late-time, optical spectra of type Ia supernovae revealed surprisingly narrow absorption features which only become visible a few months after maximum light. These features, most clearly seen in the late-time spectra of the bright, recent type Ia supernovae ASASSN-14lp and SN 2017bzc, appear as narrow absorptions at ~4840 A, ~5000 A, and as a sharp inflection at ~4760 A on the red side of the prominent late-time 4700 A feature. A survey of on-line archival data revealed similar features present in the spectra of ten other normal and 91T-like SNe Ia, including SN 2011fe. Unlike blue spectral features which exhibit progressive red-ward shifts, these narrow absorptions remain at the same wavelength from epoch to epoch for an individual SN, but can appear at slightly different wavelengths for each object. These features are also transient, appearing and then fading in one to three months. After ruling out instrumental, data reduction, and atmospheric affects, we discuss possible explanations including progenitor mass-loss material, interaction with material from previous novae events, and absorption by large discrete clumps of high-velocity Fe-rich ejecta.

Using late-time optical and near-infrared spectra to constrain Type Ia supernova explosion properties

The late-time spectra of Type Ia supernovae (SNe Ia) are powerful probes of the underlying physics of their explosions. We investigate the late-time optical and near-infrared spectra of seven SNe Ia obtained at the VLT with XShooter at $>$200 d after explosion. At these epochs, the inner Fe-rich ejecta can be studied. We use a line-fitting analysis to determine the relative line fluxes, velocity shifts, and line widths of prominent features contributing to the spectra ([Fe II], [Ni II], and [Co III]). By focussing on [Fe II] and [Ni II] emission lines in the ~7000-7500 \AA\ region of the spectrum, we find that the ratio of stable [Ni II] to mainly radioactively-produced [Fe II] for most SNe Ia in the sample is consistent with Chandrasekhar-mass delayed-detonation explosion models, as well as sub-Chandrasekhar mass explosions that have metallicity values above solar. The mean measured Ni/Fe abundance of our sample is consistent with the solar value. The more highly ionised [Co III] emission lines are found to be more centrally located in the ejecta and have broader lines than the [Fe II] and [Ni II] features. Our analysis also strengthens previous results that SNe Ia with higher Si II velocities at maximum light preferentially display blueshifted [Fe II] 7155 \AA\ lines at late times. Our combined results lead us to speculate that the majority of normal SN Ia explosions produce ejecta distributions that deviate significantly from spherical symmetry.

Pure iron grains are rare in the universe.

The abundant forms in which the major elements in the universe exist have been determined from numerous astronomical observations and meteoritic analyses. Iron (Fe) is an exception, in that only depletion of gaseous Fe has been detected in the interstellar medium, suggesting that Fe is condensed into a solid, possibly the astronomically invisible metal. To determine the primary form of Fe, we replicated the formation of Fe grains in gaseous ejecta of evolved stars by means of microgravity experiments. We found that the sticking probability for the formation of Fe grains is extremely small; only a few atoms will stick per hundred thousand collisions so that homogeneous nucleation of metallic Fe grains is highly ineffective, even in the Fe-rich ejecta of type Ia supernovae. This implies that most Fe is locked up as grains of Fe compounds or as impurities accreted onto other grains in the interstellar medium.

XMM–Newtonlarge programme on SN1006 – II. Thermal emission

Based on the XMM-Newton large program on SN1006 and our newly developed spatially resolved spectroscopy tools (Paper~I), we study the thermal emission from ISM and ejecta of SN1006 by analyzing the spectra extracted from 583 tessellated regions dominated by thermal emission. With some key improvements in spectral analysis as compared to Paper~I, we obtain much better spectral fitting results with less residuals. The spatial distributions of the thermal and ionization states of the ISM and ejecta show different features, which are consistent with a scenario that the ISM (ejecta) is heated and ionized by the forward (reverse) shock propagating outward (inward). Different elements have different spatial distributions and origins, with Ne mostly from the ISM, Si and S from the ejecta, and O and Mg from both ISM and ejecta. Fe L-shell lines are only detected in a small shell-like region SE to the center of SN1006, indicating that most of the Fe-rich ejecta has not yet or just recently been reached by the reverse shock. The overall ejecta abundance patterns for most of the heavy elements, except for Fe and sometimes S, are consistent with typical Type~Ia SN products. The NW half of the SNR interior probably represents a region with turbulently mixed ISM and ejecta, so has enhanced emission from O, Mg, Si, S, lower ejecta temperature, and a large diversity of ionization age. In addition to the asymmetric ISM distribution, an asymmetric explosion of the progenitor star is also needed to explain the asymmetric ejecta distribution.

MODELING SNR CASSIOPEIA A FROM THE SUPERNOVA EXPLOSION TO ITS CURRENT AGE: THE ROLE OF POST-EXPLOSION ANISOTROPIES OF EJECTA

ABSTRACT The remnants of core-collapse supernovae (SNe) have complex morphologies that may reflect asymmetries and structures developed during the progenitor SN explosion. Here we investigate how the morphology of the supernova remnant Cassiopeia A (Cas A) reflects the characteristics of the progenitor SN with the aim of deriving the energies and masses of the post-explosion anisotropies responsible for the observed spatial distribution of Fe and Si/S. We model the evolution of Cas A from the immediate aftermath of the progenitor SN to the three-dimensional interaction of the remnant with the surrounding medium. The post-explosion structure of the ejecta is described by small-scale clumping of material and larger-scale anisotropies. The hydrodynamic multi-species simulations consider an appropriate post-explosion isotopic composition of the ejecta. The observed average expansion rate and shock velocities can be well reproduced by models with ejecta mass M ej ≈ 4M ⊙ and explosion energy E SN ≈ 2.3 × 1051 erg. The post-explosion anisotropies (pistons) reproduce the observed distributions of Fe and Si/S if they had a total mass of ≈0.25 M ⊙ and a total kinetic energy of ≈1.5 × 1050 erg. The pistons produce a spatial inversion of ejecta layers at the epoch of Cas A, leading to the Si/S-rich ejecta physically interior to the Fe-rich ejecta. The pistons are also responsible for the development of the bright rings of Si/S-rich material which form at the intersection between the reverse shock and the material accumulated around the pistons during their propagation. Our result supports the idea that the bulk of asymmetries observed in Cas A are intrinsic to the explosion.

Two evolved supernova remnants with newly identified Fe-rich cores in the Large Magellanic Cloud

Aims. We present a multi-wavelength analysis of the evolved supernova remnants MCSNR J0506-7025 and MCSNR J0527-7104 in the Large Magellanic Cloud. Methods. We used data from XMM-Newton, the Australian Telescope Compact Array, and the Magellanic Cloud Emission Line Survey to study their broadband emission and used Spitzer and HI data to gain a picture of their environments. We performed a multi-wavelength morphological study and detailed radio and X-ray spectral analyses to determine their physical characteristics. Results. Both remnants were found to have bright X-ray cores, dominated by Fe L-shell emission, consistent with reverse shock heated ejecta with determined Fe masses in agreement with Type Ia explosion yields. A soft X-ray shell, consistent with swept-up interstellar medium, was observed in MCSNR J0506-7025, suggestive of a remnant in the Sedov phase. Using the spectral fit results and the Sedov self-similar solution, we estimated the age of MCSNR J0506-7025 to be ~16-28 kyr, with an initial explosion energy of (0.07-0.84)x10^51 erg. A soft shell was absent in MCSNR J0527-7104, with only ejecta emission visible in an extremely elongated morphology extending beyond the optical shell. We suggest that the blast wave has broken out into a low density cavity, allowing the shock heated ejecta to escape. We found that the radio spectral index of MCSNR J0506-7025 is consistent with the standard ~0.5 for SNRs. Radio polarisation at 6 cm indicates a higher degree of polarisation along the western front and at the eastern knot, with a mean fractional polarisation across the remnant of P~(20 \pm 6)%. Conclusions. The detection of Fe-rich ejecta in the remnants suggests that both resulted from Type Ia explosions. The newly identified Fe-rich cores in MCSNR J0506-7025 and MCSNR J0527-7104 makes them members of the expanding class of evolved Fe-rich remnants in the Magellanic Clouds.

THE 2D DISTRIBUTION OF IRON-RICH EJECTA IN THE REMNANT OF SN 1885 IN M31

We present Hubble Space Telescope (HST) ultraviolet Fe I and Fe II images of the remnant of Supernova 1885 (S And) which is observed in absorption against the bulge of the Andromeda galaxy, M31. We compare these Fe I and Fe II absorption line images to previous HST absorption images of S And, of which the highest quality and theoretically cleanest is Ca II H & K. Because the remnant is still in free expansion, these images provide a 2D look at the distribution of iron synthesized in this probable Type Ia explosion, thus providing insights and constraints for theoretical SN Ia models. The Fe I images show extended absorption offset to the east from the remnant's center as defined by Ca II images and is likely an ionization effect due to self-shielding. More significant is the remnant's apparent Fe II distribution which consists of four streams or plumes of Fe-rich material seen in absorption that extend from remnant center out to about 10,000 km/s. This is in contrast to the remnant's Ca II absorption, which is concentrated in a clumpy, roughly spherical shell at 1000 to 5000 km/s but which extends out to 12,500 km/s. The observed distributions of Ca and Fe rich ejecta in the SN 1885 remnant are consistent with delayed detonation white dwarf models. The largely spherical symmetry of the Ca-rich layer argues against a highly anisotropic explosion as might result from a violent merger of two white dwarfs.

High spatial resolution spectroscopy of G292.0+1.8 with Chandra

We present high spatial resolution X-ray spectroscopy of supernova remnant G292.0+1.8 made with Chandra observations. The X-ray emitting region of this remnant was divided into 25×25 pixels with a scale of 20″ ×20″ each. Spectra of 328 pixels were created and fitted with an absorbed one component non-equilibrium ionization model. With the spectral analysis results, we obtained maps of absorbing column density, temperature, ionization age and abundances for O, Ne, Mg, Si, S and Fe. The abundances of O, Ne and Mg show tight correlations between each other in the range of about two orders of magnitude, suggesting that they are all from explosive C/Ne burning. Meanwhile, the abundances of Si and S are also well correlated, indicating that they are the ashes of explosive O-burning or incomplete Si-burning. The Fe emission lines are not prominent in the whole remnant, and their abundance is significantly reduced, indicating that the reverse shock may not have propagated to the Fe-rich ejecta. Based on relative abundances of O, Ne, Mg, Si and Fe to Si, we suggest a progenitor mass of 25 – 30 M⊙ for this remnant.

DISCRIMINATING THE PROGENITOR TYPE OF SUPERNOVA REMNANTS WITH IRON K-SHELL EMISSION

Supernova remnants (SNRs) retain crucial information about both their parent explosion and circumstellar material left behind by their progenitor. However, the complexity of the interaction between supernova ejecta and ambient medium often blurs this information, and it is not uncommon for the basic progenitor type (Ia or core-collapse) of well-studied remnants to remain uncertain. Here we present a powerful new observational diagnostic to discriminate between progenitor types and constrain the ambient medium density of SNRs solely using Fe K-shell X-ray emission. We analyze all extant Suzaku observations of SNRs and detect Fe K alpha emission from 23 young or middle-aged remnants, including five first detections (IC 443, G292.0+1.8, G337.2-0.7, N49, and N63A). The Fe K alpha centroids clearly separate progenitor types, with the Fe-rich ejecta in Type Ia remnants being significantly less ionized than in core-collapse SNRs. Within each progenitor group, the Fe K alpha luminosity and centroid are well correlated, with more luminous objects having more highly ionized Fe. Our results indicate that there is a strong connection between explosion type and ambient medium density, and suggest that Type Ia supernova progenitors do not substantially modify their surroundings at radii of up to several parsecs. We also detect a K-shell radiative recombination continuum of Fe in W49B and IC 443, implying a strong circumstellar interaction in the early evolutionary phases of these core-collapse remnants.

Suzaku View of the Supernova Remnant RCW 86: X-Ray Studies of Newly-Discovered Fe-Rich Ejecta

Abstract 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 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 1–2 $\ M_{\odot}$ for the typical explosion energy of $\sim\ $ 1 $\times$ 10 $^{51}\ $ erg. The integrated flux of the Fe-K emission from the entire SNR roughly corresponds to a total Fe mass of about 1 $\ M_{\odot}$ . 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.