{
  "abstract": "Collisionless shocks confine the particles they accelerate with the upstream wave field they themselves drive. Streaming particles resonantly amplify Alfvén waves, and the waves then confine the same particles by pitch-angle scattering. The rigidity a shock precursor can hold is therefore capped by how fast those waves grow, and that coupling has not previously been constrained in situ at any interplanetary shock. Here, we report Parker Solar Probe measurements of a fast, near-parallel coronal mass ejection-driven shock at 0.24 au on 2023 March 13 that constrain this wave–particle coupling through the energetic-particle population it accelerates. We measure the spectral folding energy, the boundary between the confined and the upstream-escaping protons, and find that it falls from ∼6 to ∼1.5 MeV as E fold ∝ Δ t α with α ≃ 0.34, where Δ t is the time remaining before the shock arrival. One precursor convective time before the shock arrival, this boundary is at E c ≃ 2.46 MeV, defining a characteristic confinement energy for the precursor of scale L EP . Read through the quasi-linear marginal-stability condition; the same evolution implies a resonant wave-growth timescale τ growth ( E ) ∝ E 1/ α ≃ E 2.92 that exceeds the precursor convective time above E c . The postshock pitch-angle anisotropy reverses its sign across the same confinement–escape transition at 2–5 MeV. The rigidity to which a shock precursor can confine particles is therefore set, in situ, by how quickly the streaming population builds its own confining waves.",
  "abstract_shown": true,
  "affiliations": [
    "The Johns Hopkins University Applied Physics Laboratory",
    "University of Turku",
    "University of California",
    "Eureka Scientific",
    "Ben Gurion University of the Negev",
    "Centre for mathematical Plasma Astrophysics",
    "California Institute of Technology",
    "Princeton University"
  ],
  "article_type": null,
  "arxiv": null,
  "author_total": 14,
  "authors": [
    {
      "affs": [
        0
      ],
      "name": "A. Kouloumvakos",
      "orcid": "0000-0001-6589-4509"
    },
    {
      "affs": [
        1
      ],
      "name": "I. C. Jebaraj",
      "orcid": "0000-0002-0606-7172"
    },
    {
      "affs": [
        2,
        3
      ],
      "name": "M. A. Malkov",
      "orcid": "0000-0001-6360-1987"
    },
    {
      "affs": [
        0
      ],
      "name": "G. D. Berland",
      "orcid": "0000-0001-6010-6374"
    },
    {
      "affs": [
        4
      ],
      "name": "M. Gedalin",
      "orcid": "0000-0003-1236-4787"
    },
    {
      "affs": [
        5
      ],
      "name": "N. Wijsen",
      "orcid": "0000-0001-6344-6956"
    },
    {
      "affs": [
        6
      ],
      "name": "C. M. S. Cohen",
      "orcid": "0000-0002-0978-8127"
    },
    {
      "affs": [
        2
      ],
      "name": "O. V. Agapitov",
      "orcid": "0000-0001-6427-1596"
    },
    {
      "affs": [
        7
      ],
      "name": "D. J. McComas",
      "orcid": "0000-0001-6160-1158"
    },
    {
      "affs": [
        0
      ],
      "name": "D. G. Mitchell",
      "orcid": "0000-0003-1960-2119"
    },
    {
      "affs": [
        1
      ],
      "name": "E. Husidic",
      "orcid": "0000-0002-1349-3663"
    },
    {
      "affs": [
        1
      ],
      "name": "S. Yadav",
      "orcid": "0009-0003-9858-5720"
    },
    {
      "affs": [
        0
      ],
      "name": "M. E. Hill",
      "orcid": "0000-0002-5674-4936"
    },
    {
      "affs": [
        0
      ],
      "name": "R. McNutt",
      "orcid": "0000-0002-4722-9166"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/907dz1twqfdx0.bib",
  "cited_by": 0,
  "doi": "10.3847/2041-8213/aeaf56",
  "fulltext_url": null,
  "id": "907dz1twqfdx0",
  "issns": [
    "2041-8205",
    "2041-8213"
  ],
  "landing_url": "https://iopscience.iop.org/article/10.3847/2041-8213/aeaf56",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "https://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "openalex",
      "3103|Solar and Space Plasma Dynamics"
    ]
  ],
  "openalex": "W7220923776",
  "pdf_url": "https://iopscience.iop.org/article/10.3847/2041-8213/aeaf56/pdf",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-21",
  "publisher": "American Astronomical Society",
  "ris": "https://research.draconitic.com/paper/907dz1twqfdx0.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:18:13Z",
      "native_id": "10.3847/2041-8213/aeaf56",
      "source": "crossref",
      "url": "https://iopscience.iop.org/article/10.3847/2041-8213/aeaf56"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "openalex:3103|Solar and Space Plasma Dynamics",
      "subfield": "stellar"
    }
  ],
  "title": "Wave-growth-limited Particle Confinement in a Near-parallel Interplanetary Shock Observed by Parker Solar Probe",
  "title_text": "Wave-growth-limited Particle Confinement in a Near-parallel Interplanetary Shock Observed by Parker Solar Probe",
  "type": "peer-reviewed",
  "updated_at": "2026-10-30T12:18:13Z",
  "url": "https://research.draconitic.com/paper/907dz1twqfdx0",
  "venue": "The Astrophysical Journal Letters",
  "versions": []
}