{
  "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 $^{56}$Ni mixing in supernovae and r-process material in collapsars. Moving $^{56}$Ni 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 $f_{\\rm Ni}$, while $\\Mni$ remains stable. If opacity is free, the fully mixed case is recovered with $κ^{\\rm fit}/κ^{\\rm input}\\simeq0.24$. 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 $\\gtrsim 30^\\circ$ from the equatorial plane.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": "Journal reference: Mon Not R Astron Soc (2026)",
  "arxiv": "2606.23780",
  "author_total": 1,
  "authors": [
    {
      "name": "Nikhil Sarin"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/avaqbpwwgnvj0.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2606.23780",
  "fulltext_url": null,
  "id": "avaqbpwwgnvj0",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2606.23780",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "http://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "astro-ph.HE"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2606.23780",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-11",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/avaqbpwwgnvj0.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:25:31Z",
      "native_id": "2606.23780",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2606.23780"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.HE",
      "subfield": "high-energy-astrophysics"
    }
  ],
  "title": "Signatures of $^{56}$Ni Mixing and Neutron-rich Ejecta in Supernovae",
  "title_text": "Signatures of ^56Ni Mixing and Neutron-rich Ejecta in Supernovae",
  "type": "preprint",
  "updated_at": "2026-10-30T12:25:31Z",
  "url": "https://research.draconitic.com/paper/avaqbpwwgnvj0",
  "venue": "arXiv",
  "versions": [
    {
      "doi": "10.1093/mnras/stag1722",
      "pid": null,
      "relation": "published-as",
      "title": null,
      "venue": null
    }
  ]
}