We present three-dimensional kinematic reconstructions of optically emitting material in the young Galactic supernova remnant Cassiopeia A (Cas A). These Doppler maps have the highest spectral and spatial resolutions of any previous survey of Cas A and represent the most complete catalog of its optically emitting material to date. We confirm that the bulk of Cas A's optically bright ejecta populate a torus-like geometry tilted approximately 30 degrees with respect to the plane of the sky with a -4000 to +6000 km/s radial velocity asymmetry. Near-tangent viewing angle effects and an inhomogeneous surrounding CSM/ISM environment suggest that this geometry and velocity asymmetry may not be faithfully representative of the remnant's true 3D structure or the kinematic properties of the original explosion. The majority of the optical ejecta are arranged in several well-defined and nearly circular ring-like structures with diameters between approximately 30 arcsec (0.5 pc) and 2 arcmin (2 pc). These ejecta rings appear to be a common phenomenon of young core-collapse remnants and may be associated with post-explosion input of energy from plumes of radioactive 56Ni-rich ejecta that rise, expand, and compress non-radioactive material. Our optical survey also encompassed Cas A's faint outlying ejecta knots and exceptionally high-velocity NE and SW streams of S-rich debris often referred to as `jets'. These outer knots, which exhibit a chemical make-up suggestive of an origin deep within the progenitor star, appear to be arranged in opposing and wide-angle outflows with opening half-angles of approximately 40 degrees.
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 …
Fermi observations of Cassiopeia and Cepheus: gamma-ray diffuse emission in the outer Galaxy
我们利用费米大天区望远镜（LAT）的测量研究了银河系第二象限（100度< l < 145度和-15度< b < 30度）区域的星际伽马射线发射。这一区域包括仙后座、仙王座和北极星耀斑的黄金带云，以及几个旋臂中距离较远的大型原子和分子复合物。本地臂、英仙座臂和外臂之间的运动学速度分离良好，并且每个臂中都存在大质量的复合物，使得这个区域非常适合探测太阳圈以外的星际介质的伽马射线发射。LAT前所未有的灵敏度和角分辨率提供了更好的约束宇宙射线密度的梯度和增加的CO到H2的转换因子，Xco，在外星系。
Cassiopeia A is one of the best-studied supernova remnants. Its shocked ejecta emits brightly in radio and X-rays. Its unshocked ejecta can be studied through infrared emission, the radio-active decay of $^{44}$Ti, and low frequency free-free absorption due to cold gas internal to the shell. Free-free absorption is affected by the mass, geometry, temperature, and ionisation conditions in the absorbing gas. Observations at the lowest radio frequencies constrain a combination of these properties. We use LOFAR LBA observations at 30-77 MHz and L-band VLA observations to compare $u-v$-matched imag…
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…
We present a long-exposure (~10 hr) image of the supernova (SN) remnant Cassiopeia A (Cas A) obtained with the UKIRT 3.8-m telescope using a narrow band filter centered at 1.644 um emission. The passband contains [Fe II] 1.644 um and [Si I] 1.645 um lines, and our `deep [Fe II]+[Si I] image' provides an unprecedented panoramic view of Cas A, showing both shocked and unshocked SN ejecta together with shocked circumstellar medium at subarcsec (~0.7 arcsec or 0.012 pc) resolution. The diffuse emission from the unshocked SN ejecta has a form of clumps, filaments, and arcs, and their spatial distri…
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）
Mixing above the proto-neutron star is believed to play an important role in the supernova engine, and this mixing results in a supernova explosion with asymmetries. Elements produced in the innermost ejecta, e.g., ${}^{56}$Ni and ${}^{44}$Ti, provide a clean probe of this engine. The production of ${}^{44}$Ti is particularly sensitive to the exact production pathway and, by understanding the available pathways, we can use ${}^{44}$Ti to probe the supernova engine. Using thermodynamic trajectories from a three-dimensional supernova explosion model, we review the production of these elements an…
Fermi observations of Cassiopeia and Cepheus: diffuse gamma-ray emission in the outer Galaxy
本文分析了费米大天区望远镜在银河系第二象限100度< l < 145度和-15度< b < +30度区域测量到的星际伽马射线辐射。这一区域包括仙后座、仙王座和北极星耀斑的显著的古尔德带云，以及更远距离的原子和分子复合体，如英仙座臂中与NGC 7538相关的复合体。而且每个星系中都存在大质量的复合体，这使得这个区域非常适合探测宇宙射线和太阳圈以外的星际介质。古尔德带中气体的伽马射线发射率光谱与基于当地测量的宇宙射线光谱的预期一致。伽马射线发射率从古尔德带到英仙座臂逐渐降低，但测量到的梯度比宇宙射线源在银河系内部达到峰值的预期要平坦，这一点由天文学家提出。我们发现Xco=N（H2）/W（CO）的转换因子从古尔德带的（0.87 +- 0.05）10^20 cm^-2（K km s^-1）^-1增加到英仙座臂的（1.9 +- 0.2）10^20 cm^-2（K km s^-1）^-1。在古尔德带中，通过相关的过量尘埃和伽马射线发射，发现了没有被无线电和微波探测正确追踪的暗气体：其质量约为CO追踪质量的50%。
Cassiopeia A (Cas A) is one of the best studied young Galactic supernova remnants. While providing a rare opportunity to study in detail the remnant of a Type IIb supernova, questions remain regarding the nature of its progenitor, its mass-loss history, and its pre-SN evolution. Here we present an optical investigation of the circumstellar environment around Cas A and find clumpy and filamentary Halpha emission nebulosities concentrated 10-15 pc (10-15 arcminutes) to the north and east. First reported by Minkowski as a faint H II region, these nebulosities exhibit distinct morphological and sp…
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）
Supernova remnants (SNRs) offer the means to study supernovae (SNe) long after the original explosion and can provide a unique insight into the mechanism that governs these energetic events. In this work, we examine the morphologies of X-ray emission from different elements found in the youngest known core-collapse (CC) SNR in the Milky Way, Cassiopeia A. The heaviest elements exhibit the highest levels of asymmetry, which we relate to the burning process that created the elements and their proximity to the center of explosion. Our findings support recent model predictions that the material cl…
我们重新审视长期存在的问题的仙后座A超新星（SN）的日期，鉴于最近的索赔，它可能是1630年的“正午星”看到在国王查尔斯二世的诞生。我们不支持这种鉴定，基于IIb型超新星的预期亮度（太暗而无法在白天看到），喷出物的外推运动（与1650年之前的日期不一致），缺乏任何科学的后续观测，亚洲档案中没有任何提及它。1630年正午星事件的起源（如果是真的）仍然是一个谜; 1630年6月有一颗明亮的彗星，但没有证据确定它是否在白天可见。相反，我们目前法国的报告，卡西尼号在仙后座发现了一颗4等星在1671年或之前不久，这是没有看到之前或之后。亮度与我们对Cas A SN的预期一致;日期与喷出物的外推运动一致。我们认为，这个来源可能是长期寻找的SN。
Supernovae (SNe) with photospheric spectra devoid of Hydrogen and Helium features are generally classified as Type Ic SNe (SNe Ic). However, there is ongoing debate as to whether Helium can be hidden in the ejecta of SNe Ic (that is, Helium is present in the ejecta, but produces no obvious features in the spectra). We present the first application of the fast, 1-D radiative transfer code TARDIS to a SN Ic, and we investigate the question of how much Helium can be hidden in the outer layers of the SN Ic ejecta. We generate TARDIS models for the nearby, well-observed, and extensively modeled SN …
An excess of flux (i.e. a bump) in the early light curves of type Ia supernovae has been observed in a handful of cases. Multiple scenarios have been proposed to explain this. It has been shown that for at least one object (SN~2018oh) the excess emission observed could be the result of a large amount of $^{56}$Ni in the outer ejecta ($\sim$0.03~$M_{\rm{\odot}}$). We present a series of model light curves and spectra for ejecta profiles containing $^{56}$Ni shells of varying masses (0.01, 0.02, 0.03, and 0.04~$M_{\rm{\odot}}$) and widths. We find that even for our lowest mass $^{56}$Ni shell, a…
We present a three-dimensional kinematic reconstruction of the optically-emitting, oxygen-rich ejecta of supernova remnant N132D in the Large Magellanic Cloud. Data were obtained with the 6.5 m Magellan telescope in combination with the IMACS+GISMO instrument and survey [O III] $λλ$4959,5007 line emission in a ${\sim}$3$^{\prime}~\times$ 3$^{\prime}$ region centered on N132D. The spatial and spectral resolution of our data enable detailed examination of the optical ejecta structure. The majority of N132D's optically bright oxygen ejecta are arranged in a torus-like geometry tilted approximatel…
