The Cassiopeia A supernova remnant has a complex structure, manifesting the multidimensional nature of core-collapse supernova explosions. To further understand this, we carried out near-infrared multi-object spectroscopy on the ejecta knots located in the "northeastern (NE) jet" and the "Fe K plume" regions, which are two distinct features in the outer eastern area of the remnant. Our study reveals that the knots exhibit varying ratios of [S II] 1.03 $μ$m, [P II] 1.189 $μ$m, and [Fe II] 1.257 $μ$m lines depending on their locations within the remnant, suggesting regional differences in elemental composition. Notably, the knots in the NE jet are mostly 'S-rich' with weak or no [P II] lines, implying that they originated below the explosive Ne burning layer, consistent with the results of previous studies. We detected no ejecta knots exhibiting only [Fe II] lines in the NE jet area that are expected in the jet-driven SN explosion model. Instead, we discovered a dozen 'Fe-rich' knots in the Fe K plume area. We propose that they are dense knots produced by a complete Si burning with $α$-rich freezeout in the innermost region of the progenitor and ejected with the diffuse X-ray emitting Fe ejecta but decoupled after crossing the reverse shock. In addition to these metal-rich ejecta knots, several knots emitting only He I 1.083 $μ$m lines were detected, and their origin remains unclear. We also detected three extended H emission features of circumstellar or interstellar origin in this area and discuss its association with the supernova remnant.
Recent multi-dimensional simulations suggest that high-entropy buoyant plumes help massive stars to explode. Outwardly protruding iron-rich fingers in the galactic supernova remnant Cassiopeia A are uniquely suggestive of this picture. Detecting signatures of specific elements synthesized in the high-entropy nuclear burning regime (i.e., $α$-rich freeze out) would be among the strongest substantiating evidence. Here we report the discovery of such elements, stable Ti and Cr, at a confidence level greater than 5$σ$ in the shocked high-velocity iron-rich ejecta of Cassiopeia A. We found the obse…
The central strong activities in core-collapse supernovae expect to produce the overturning of the Fe- and Si/O-rich ejecta during the supernova explosion based on multi-dimensional 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-…
We analyze and model the infrared spectrum of the Cassiopeia A supernova remnant, with the aim of determining the masses of various elements in the unshocked ejecta. In this way we complement the survey of the X-ray emitting ejecta of Hwang & Laming (2012) to provide a complete census of the elemental composition of the Cas A ejecta. We calculate photoionization-recombination equilibria to determine the ionization balance of various elements in the ejecta as a function of density, using the X-ray and UV emission from the forward and reverse shocks as the ionizing radiation. With the assumption…
The Circumstellar Medium of Cassiopeia A Inferred from the Outer Ejecta Knot Properties
利用1 Ms Chandra观测研究了仙后座A超新星遗迹中星周介质密度分布对外层喷射物结X射线辐射的影响。使用类似的技术，在以前的论文中设计的一些径向系列的喷出物结在不同的位置周围的残余物的光谱进行分析。对于与r^-2成比例的星周密度分布，我们可以得到与我们的数据相匹配的结果，这是由红超巨星的稳定致密风引起的，但是如果我们在模型中引入一个围绕着前身星的小的（0.2-0.3 pc）中心空腔，则可以改善这种匹配。如果在爆炸前的一小段时间内，母星会释放出快速稀薄的恒星风，那么就可能出现这样的轮廓。我们回顾了支持这一结论的其他证据。光谱还表明广泛存在的富铁等离子体，据推测是由完整的硅燃烧在爆炸过程中，可能通过富阿尔法冻结。该成分通常与比大部分富含O和Si的喷出物更热和更高度电离的气体相关联。
Recent simulations have shown that asymmetries in the ejecta distribution of supernova remnants (SNR) can still reflect asymmetries from the initial supernova explosion. Thus, their study provides a great means to test and constrain model predictions in relation to the distributions of heavy elements or the neutron star kicks, both of which are key to better understanding the explosion mechanisms in core-collapse supernovae. The use of a novel blind source separation method applied to the megasecond X-ray observations of the well-known Cassiopeia A SNR has revealed maps of the distribution of …
Abridged. We aim at exploring 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) during the first second after core bounce. We coupled a 3D HD model of a neutrino-driven SN explosion with 3D MHD/HD simulations of the remnant formation. The simulations cover 2000 years of expansion and include all physical processes relevant to describe the complexities in the SN evolution and the subsequent interaction of the stellar debri…
Mapping plasma properties of Cassiopeia A with XRISM/Resolve: a Bayesian analysis via UltraSPEX
University of Amsterdam（阿姆斯特丹大学）；SRON Netherlands Institute for Space Research（荷兰空间研究所）；The University of Tokyo（东京大学）；Harvard-Smithsonian Center for Astrophysics（哈佛-史密森天体物理中心）；Meiji University（明治大学）
Deciphering the "Green Monster" in Cassiopeia A: Puncturing and sculpting a heterogeneous circumstellar shell
INAF – Osservatorio Astronomico di Palermo（意大利国家天体物理研究所巴勒莫天文台）；Max-Planck-Institut für Astrophysik（马克斯·普朗克天体物理学研究所）；Purdue University（普渡大学）；Ghent University（根特大学）；Princeton University（普林斯顿大学）；Dartmouth College（达特茅斯学院）；Seoul National University（首尔国立大学）；Università degli Studi di Palermo（巴勒莫大学）
Observations of the SNR Cassiopeia A (Cas A) show asymmetries in the reverse shock that cannot be explained by models describing a remnant expanding through a spherically symmetric wind of the progenitor star. We investigate whether a past interaction of Cas A with an asymmetric circumstellar shell can account for the observed asymmetries. We performed 3D MHD simulations that describe the remnant evolution from the SN to its interaction with a circumstellar shell. The initial conditions are provided by a 3D neutrino-driven SN model whose morphology resembles Cas A. We explored the parameter sp…
We present X-ray analysis of the ejecta of supernova remnant G350.1$-$0.3 observed with Chandra and Suzaku, and clarify the ejecta's kinematics over a decade and obtain a new observational clue to understanding the origin of the asymmetric explosion. Two images of Chandra X-ray Observatory taken in 2009 and 2018 are analyzed in several methods, and enable us to measure the velocities in the plane of the sky. A maximum velocity is 4640$\pm$290 km s$^{-1}$ (0.218$\pm$0.014 arcsec yr$^{-1}$) in the eastern region in the remnant. These findings trigger us to scrutinize the Doppler effects in the s…
