{
  "abstract": "Shock breakout (SBO) occurs when a radiation-mediated shock wave, formed during a core-collapse supernova (SN) explosion, breaks out from the stellar surface of the progenitor or from the circumstellar material (CSM), if the CSM is optically thick. The X-ray outburst XRO 080109, associated with a Type Ib/c SN 2008D, has been suggested to be an SBO event from a regular supernova. The recent detection of EP260321a, associated with a broad-lined Type Ic SN 2026gzf, by the Einstein Probe adds a new SBO event. However, the two SBO events differ markedly in their spectra, energetics, late-time radio emission and early optical emission within the first day. We show that the non-detections in radio follow-up observations of EP260321a imply a shock velocity $\\lesssim0.1c$, whereas the radio data of XRO 080109 suggest a shock velocity of $\\simeq0.2c$. These velocities are consistent with those inferred from the properties of the X-ray outbursts and explain the difference in their X-ray spectra. The X-ray energy and duration of EP260321a indicate that the shock breaks out from the CSM at a radius of $\\sim2\\times10^{13}\\ {\\rm cm}$. Its bright optical emission at $t\\lesssim1\\ {\\rm d}$ can be explained by cooling emission from a dense, extended CSM shell heated by the radiation-mediated shock, requiring a total CSM mass of $\\sim0.06M_\\odot$, substantially larger than that inferred for XRO 080109. Finally, the lower shock velocity and larger CSM mass can be unified in a picture in which a more massive CSM decelerates the radiation-mediated shock more significantly before it breaks out.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": "Journal reference: ApJL 1008, L63 (2026)",
  "arxiv": "2610.30973",
  "author_total": 3,
  "authors": [
    {
      "name": "Cui-Yuan Dai"
    },
    {
      "name": "Xiang-Yu Wang"
    },
    {
      "name": "Jian-He Zheng"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/3yqr8ahqfhjh4.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2610.30973",
  "fulltext_url": null,
  "id": "3yqr8ahqfhjh4",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2610.30973",
  "language": null,
  "licence": "LicenseRef-arXiv-nonexclusive-1.0",
  "licence_label": "arXiv licence",
  "licence_source": "article",
  "licence_url": "http://arxiv.org/licenses/nonexclusive-distrib/1.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "astro-ph.HE"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2610.30973",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-22",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/3yqr8ahqfhjh4.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:34:34Z",
      "native_id": "2610.30973",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2610.30973"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.HE",
      "subfield": "high-energy-astrophysics"
    }
  ],
  "title": "Weak Radio and Bright Early Optical Emission in EP260321a: A Comparative Study with XRO 080109 Reveals the Role of Circumstellar Material Mass",
  "title_text": "Weak Radio and Bright Early Optical Emission in EP260321a: A Comparative Study with XRO 080109 Reveals the Role of Circumstellar Material Mass",
  "type": "preprint",
  "updated_at": "2026-10-30T12:34:34Z",
  "url": "https://research.draconitic.com/paper/3yqr8ahqfhjh4",
  "venue": "arXiv",
  "versions": [
    {
      "doi": "10.3847/2041-8213/ae9eba",
      "pid": null,
      "relation": "published-as",
      "title": null,
      "venue": null
    }
  ]
}