The Three-Dimensional Structure of Interior Ejecta in Cassiopeia a at High Spectral Resolution

Abstract

We used the Spitzer Space Telescope's Infrared Spectrograph to create a high-resolution spectral map of the central region of the Cassiopeia A (Cas A) supernova remnant, allowing us to make a Doppler reconstruction of its threedimensional structure. The ejecta responsible for this emission have not yet encountered the remnant's reverse shock or the circumstellar medium, making it an ideal laboratory for exploring the dynamics of the supernova explosion itself. We observe that the O, Si, and S ejecta can form both sheet-like structures and filaments. Si and O, which come from different nucleosynthetic layers of the star, are observed to be coincident in velocity space in some regions, and separated by 500 km s −1 or more in others. Ejecta traveling toward us are, on average, ∼900 km s −1 slower than the material traveling away from us. We compare our observations to recent supernova explosion models and find that no single model can simultaneously reproduce all the observed features. However, models of different supernova explosions can collectively produce the observed geometries and structures of the interior emission. We use the results from the models to address the conditions during the supernova explosion, concentrating on asymmetries in the shock structure. We also predict that the back surface of Cas A will begin brightening in ∼30 years, and the front surface in ∼100 years.

The Density and Mass of Unshocked Ejecta in Cassiopeia a Through Low Frequency Radio Absorption

“…The high spectral resolution Spitzer mapping shows that the sheets are composed of thin filaments (1. 5 or 0.03 pc thick) with several filaments along any given line-ofsight (Isensee et al 2010). Therefore, we estimate the combined thickness of the front and back sheets to be of order 10 which translates to L = 0.16 pc at the distance to Cas A of 3.4 kpc Reed et al 1995).…”

“…DeLaney et al (2010) and Isensee et al (2010) showed that the unshocked ejecta, as traced by [O iv] and [Si ii] emission, are concentrated onto two thick sheets interior to the reverse shock-one front and one rear. The two sheets are separated by a much lower density region, where only a little emission is seen.…”

THE DISTRIBUTION OF RADIOACTIVE 44Ti IN CASSIOPEIA A

“…Such emission has not yet been observed (Isensee et al 2010;DeLaney et al 2014), implying either that the interior iron ejecta are so diffuse that they cannot be detected, or that they are in a higher ionization state due to photoionization from soft X-rays from the ejecta and thus cannot be observed by Spitzer, or that the ejecta are not present. Deeper observations to probe for a cold, diffuse source of iron are required to further constrain the Fe/Ti ratio in the interior of the remnant.…”

“…For the shocked ejecta, we can use the [Ar II] 6.99 μm 3D maps from Spitzer Isensee et al 2010). Seen in the plane of the sky, the ejecta forms the feature known as the "bright ring," while in 3D there are circular structures in the plane of the sky (labeled as the "north ring" and the "NE jet" structures, Figure 10).…”

Three-dimensional neutrino-driven supernovae: Neutron star kicks, spins, and asymmetric ejection of nucleosynthesis products

“…In particular, it might allow one to discriminate our gravitational tug-boat mechanism from scenarios like the neutrino-driven kicks discussed by Fryer & Kusenko (2006), who expect the stronger explosion (and thus enhanced explosive nucleosynthesis) in the direction of the NS motion. High-resolution spectral investigations of young SN remnants like Puppis A (Katsuda et al 2008(Katsuda et al , 2010, G11.2-0.3 (Moon et al 2009), and Cassiopeia A (Isensee et al 2010;DeLaney et al 2010;Rest et al 2011;Hwang & Laming 2012) in different wavebands may offer a promising perspective.…”