Element Stratification in the Middle-aged SN Ia Remnant G344.7–0.1

Abstract

Despite their importance, a detailed understanding of Type Ia supernovae (SNe Ia) remains elusive. X-ray measurements of the element distributions in supernova remnants (SNRs) offer important clues for understanding the explosion and nucleosynthesis mechanisms for SNe Ia. However, it is challenging to observe the entire ejecta mass in X-rays for young SNRs, because the central ejecta may not have been heated by the reverse shock yet. Here we present over 200 kilosecond Chandra observations of the Type Ia SNR G344.7–0.1, whose age is old enough for the reverse shock to have reached the SNR center, providing an opportunity to investigate the distribution of the entire ejecta mass. We reveal a clear stratification of heavy elements with a centrally peaked distribution of the Fe ejecta surrounded by intermediate-mass elements (IMEs: Si, S, Ar Ca) with an arc-like structure. The centroid energy of the Fe K emission is marginally lower in the central Fe-rich region than in the outer IME-rich regions, suggesting that the Fe ejecta were shock-heated more recently. These results are consistent with the prediction for standard SN Ia models, where the heavier elements are synthesized in the interior of an exploding white dwarf. We find, however, that the peak location of the Fe K emission is slightly offset to the west with respect to the geometric center of the SNR. This apparent asymmetry is likely due to the inhomogeneous density distribution of the ambient medium, consistent with our radio observations of the ambient molecular and neutral gas.

Can the Fe K-alpha Line Reliably Predict Supernova Remnant Progenitors?

“…Prior studies, including Y14, extracted the spectrum from the entire remnant, but the centroid energies extracted from different regions may not agree with the centroid from the entire remnant. Our spatially resolved fits in 3C 397 reveal statistically significant variations in the Fe Kα centroid energy up to 100 eV, spanning both the Type Ia and CC regions designated by Y14; for G344.7-0.1 the variations reached 130 eV (Fukushima et al 2020).…”

“…We find statistically significant variation in the Fe Kα centroid across various regions; the energy of the centroid varies by about 100 eV over the remnant surface. While this variation is large, we note that Fukushima et al (2020) report a variation of ∼ 130 eV for various Fe Kα centroid energies in Figure 3. A comparison of the Fe Kα centroid energies for each remnant, with the results of Y14 shown as magenta lines.…”

An Expanding Shell of Neutral Hydrogen Associated with SN 1006: Hints for the Single-Degenerate Origin and Faint Hadronic Gamma-Rays

“…Interestingly, no dense Hi clouds are adjacent to the southeast shells, where the shock velocity shows the maximum value in SN 1006 (Winkler et al 2014). We also note that the Hi intensity of SN 1006 is about 3-10 times weaker than that of the typical Type Ia SNRs interacting with Hi clouds in the Galactic plane (e.g., Sano et al 2017;Fukushima et al 2020).…”

“…The presence of dense-gas wall and the SD scenario were also supported by the rapid shock deceleration during the last ∼15 yr (Tanaka et al 2021). Subsequent CO and Hi studies found similar expanding shells of atomic and/or molecular clouds in the Type Ia SNRs RCW 86 (Sano et al 2017), N103B (Sano et al 2018;Alsaberi et al 2019), and G344.7−0.1 (Fukushima et al 2020).…”

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

“…The ionization parameter of the Fe ejecta is found to be significantly lower than that of the IME ejecta in any regions (Table 1). This is a common characteristic of SNRs Ia (e.g., Badenes et al 2007;Sawada et al 2019;Fukushima et al 2020) and indicates the stratified elemental composition with Fe at the interior so that the Fe ejecta are heated by the reverse shock more recently than the IME ejecta. Such elemental stratification is indeed observed in the radial profile shown in Figure 2.…”