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Published April 22, 2021 | Supplemental Material
Journal Article Open

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

Abstract

Recent multi-dimensional simulations suggest that high-entropy buoyant plumes help massive stars to explode. Outwardly protruding iron (Fe)-rich fingers of gas in the galactic supernova remnant 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 ejecta. These results support the operation of the convective supernova engine via neutrino heating in the supernova that produced Cassiopeia A.

Additional Information

© 2021 Nature Publishing Group. Received 15 July 2020; Accepted 24 February 2021; Published 21 April 2021. T.S. was supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI grant number JP19K14739, the Special Postdoctoral Researchers Program, and FY 2019 Incentive Research Projects in RIKEN. K.M. was supported in part by Grants-in-Aid for the Scientific Research of JSPS (grant numbers JP18H05223 and JP20H00174). S.N. is partially supported by the Grants-in-Aid for the Scientific Research of JSPS (grant KAKENHI (A) 19H00693), the RIKEN programme for Evolution of Matter in the Universe (r-EMU), and the Theoretical and Mathematical Sciences Program of RIKEN (iTHEMS). J.PH. acknowledges support for X-ray studies of supernova remnants from NASA grant NNX15AK71G to Rutgers University. T.Y. is supported in part by a Grant-in-Aid for Scientific Research of Innovative Areas (JP20H05249). H.U. is supported in part by a Grant-in-Aid for Scientific Research (JP17H01130). Data availability: All the Chandra and NuSTAR data used in this research are available from the Chandra Data Archive (https://cxc.harvard.edu/cda/) and the NuSTAR Archive (https://heasarc.gsfc.nasa.gov/docs/nustar/nustar_archive.html) in raw and reduced formats. Code availability: To analyse X-ray data with Chandra, we used public software, Chandra Interactive Analysis of Observations: CIAO (https://cxc.cfa.harvard.edu/ciao/). We used public atomic data in atomDB (http://www.atomdb.org/) and SPEX (https://www.sron.nl/astrophysics-spex). We fitted the X-ray spectra with a public package, Xspec (https://heasarc.gsfc.nasa.gov/xanadu/xspec/). We have not made publicly available codes for the hydrodynamics and nucleosynthesis of supernova explosions because they are not prepared for open use. Instead, the simulated thermodynamic profiles of the supernova explosions and the composition distributions shown in this paper are available on request. Author Contributions: T.S. wrote the manuscript with comments from all the authors and analysed the Chandra data. K.M., S.N., H.U., J.P.H. and B.J.W. made important contributions to the overall science case and manuscript. B.G. analysed the NuSTAR data and made Fig. 1. T.Y., H.U. and M.O. calculated the nucleosynthesis models. The authors declare no competing interests. Peer review information: Nature thanks Patrick Young and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Peer reviewer reports are available.

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Additional details

Created:
August 22, 2023
Modified:
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