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PreprintCC BY 4.0arXiv

Signatures of 56Ni Mixing and Neutron-rich Ejecta in Supernovae

  • Nikhil Sarin
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Abstract

Supernova lightcurves are often interpreted with one-zone radioactive-decay models that ignore a key variable that can affect interpretation and inferred parameters: the distribution of radioactive material. Using a multi-shell model, we explore the impact of 56Ni mixing in supernovae and r-process material in collapsars. Moving 56Ni outward reduces the overlying diffusion column, producing faster and brighter rises at fixed Mni, Mej, and Ek, and changes the tail through local gamma-ray leakage. A fast, bright rise is not, by itself, evidence for low ejecta mass or a requirement for engine power, with significant overlap between highly mixed and engine-powered lightcurves. One-zone fits to mixed bolometric light curves produce visually good fits but biased parameters. At fixed opacity, outward mixing is absorbed mainly by low inferred Mej and high inferred fNi, while Mni remains stable. If opacity is free, the fully mixed case is recovered with κfit/κinput≃0.24. These shifts affect inferred explosion energies and progenitor mappings, and amplified in photometric fits. Exploring collapsar r-process enrichment, we find that the signature is not always a NIR excess and depends sensitively on the nickel-powered background, radial placement, angular distribution, and viewing angle of neutron-rich ejecta. In our setup, spherical models often show optical suppression and delayed colour evolution. Our disk-wind models suggest that fast-rising on-axis GRB-SNe are poor r-process targets for equatorially confined neutron-rich winds, and become constraining only if the r-process material reaches latitudes ≳ 30∘ from the equatorial plane.

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Cite

BibTeXRIS
BibTeX
@misc{sarin2026signatures,
  title = {{Signatures of $^56$Ni Mixing and Neutron-rich Ejecta in Supernovae}},
  author = {Nikhil Sarin},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2606.23780},
  eprint = {2606.23780},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2606.23780},
  note = {CC BY 4.0},
}
RIS
TY  - UNPB
TI  - Signatures of ^56Ni Mixing and Neutron-rich Ejecta in Supernovae
AU  - Nikhil Sarin
PY  - 2026
DA  - 2026/09/11
PB  - arXiv
DO  - 10.48550/arxiv.2606.23780
UR  - https://arxiv.org/abs/2606.23780
AB  - Supernova lightcurves are often interpreted with one-zone radioactive-decay models that ignore a key variable that can affect interpretation and inferred parameters: the distribution of radioactive material. Using a multi-shell model, we explore the impact of ^56Ni mixing in supernovae and r-process material in collapsars. Moving ^56Ni outward reduces the overlying diffusion column, producing faster and brighter rises at fixed Mni, Mej, and Ek, and changes the tail through local gamma-ray leakage. A fast, bright rise is not, by itself, evidence for low ejecta mass or a requirement for engine power, with significant overlap between highly mixed and engine-powered lightcurves. One-zone fits to mixed bolometric light curves produce visually good fits but biased parameters. At fixed opacity, outward mixing is absorbed mainly by low inferred Mej and high inferred f_Ni, while Mni remains stable. If opacity is free, the fully mixed case is recovered with κ^fit/κ^input≃0.24. These shifts affect inferred explosion energies and progenitor mappings, and amplified in photometric fits. Exploring collapsar r-process enrichment, we find that the signature is not always a NIR excess and depends sensitively on the nickel-powered background, radial placement, angular distribution, and viewing angle of neutron-rich ejecta. In our setup, spherical models often show optical suppression and delayed colour evolution. Our disk-wind models suggest that fast-rising on-axis GRB-SNe are poor r-process targets for equatorially confined neutron-rich winds, and become constraining only if the r-process material reaches latitudes ≳ 30^∘ from the equatorial plane.
ER  -