NEXUS: Discovery of a Luminous Young Transient at z=5

Abstract

We report the discovery of AT 2026abck, a young transient in a star-forming galaxy at z=5.017±0.001, identified from Year-2 observations of the NEXUS JWST treasury program. AT 2026abck was detected on 2026 Aug 7 in NIRCam F200W imaging, with contemporaneous detection from parallel NIRCam F150W+F277W imaging. It brightened by >1.4 mag in F200W over ≲ 12 rest-frame days, as inferred from the last non-detection. AT 2026abck has nearly identical magnitudes of ∼27.4 mag in F150W, F200W, and F277W, and is undetected in F444W (>27.9 mag, 3σ). It is the first robustly detected z≳ 5 transient in a non-lensing field. A blackbody fit yields a hot photosphere (∼1.7×10⁴ K) with a radius of ∼7×10¹⁴ cm (∼46 au) and a bolometric luminosity of ∼3×10⁴³ erg s⁻¹. Its off-nucleus location and hot, UV-bright SED favor a core-collapse supernova origin, while its temperature and luminosity exceed those of normal SNe II at comparable early phases. We estimate that AT 2026abck was detected ∼4-10 rest-frame days after explosion. The host is an intermediate-mass (M_*≈10^9.8 M_⊙), star-forming (SFR≈20 M_⊙ yr⁻¹) galaxy on the z≈5 main sequence, ∼3.3 dex more massive than the ultra-faint host of the lensed SN Eos at z=5.13. Together, the two events show that CCSNe at z>5 occur across a wide range of host environments, and AT 2026abck demonstrates that high-cadence blank-field JWST surveys can capture high-redshift SNe during their early, UV-bright phase.

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BibTeX RIS

BibTeX

@misc{zhuang2026nexus,
  title = {{NEXUS: Discovery of a Luminous Young Transient at $z=5$}},
  author = {Ming-Yang Zhuang and Yue Shen and Lei Hu and Justin D. R. Pierel and Zhiwei Pan and Zachary Stone and Adam J. Burgasser and Xiaohui Fan and Jenny E. Greene and Junyao Li and Feige Wang},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.38373},
  eprint = {2609.38373},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.38373},
  note = {CC BY 4.0},
}

RIS

TY  - UNPB
TI  - NEXUS: Discovery of a Luminous Young Transient at z=5
AU  - Ming-Yang Zhuang
AU  - Yue Shen
AU  - Lei Hu
AU  - Justin D. R. Pierel
AU  - Zhiwei Pan
AU  - Zachary Stone
AU  - Adam J. Burgasser
AU  - Xiaohui Fan
AU  - Jenny E. Greene
AU  - Junyao Li
AU  - Feige Wang
PY  - 2026
DA  - 2026/09/29
PB  - arXiv
DO  - 10.48550/arxiv.2609.38373
UR  - https://arxiv.org/abs/2609.38373
AB  - We report the discovery of AT 2026abck, a young transient in a star-forming galaxy at z=5.017±0.001, identified from Year-2 observations of the NEXUS JWST treasury program. AT 2026abck was detected on 2026 Aug 7 in NIRCam F200W imaging, with contemporaneous detection from parallel NIRCam F150W+F277W imaging. It brightened by >1.4 mag in F200W over ≲ 12 rest-frame days, as inferred from the last non-detection. AT 2026abck has nearly identical magnitudes of ∼27.4 mag in F150W, F200W, and F277W, and is undetected in F444W (>27.9 mag, 3σ). It is the first robustly detected z≳ 5 transient in a non-lensing field. A blackbody fit yields a hot photosphere (∼1.7×10^4 K) with a radius of ∼7×10^14 cm (∼46 au) and a bolometric luminosity of ∼3×10^43 erg s^−1. Its off-nucleus location and hot, UV-bright SED favor a core-collapse supernova origin, while its temperature and luminosity exceed those of normal SNe II at comparable early phases. We estimate that AT 2026abck was detected ∼4-10 rest-frame days after explosion. The host is an intermediate-mass (M_*≈10^9.8 M_⊙), star-forming (SFR≈20 M_⊙ yr^−1) galaxy on the z≈5 main sequence, ∼3.3 dex more massive than the ultra-faint host of the lensed SN Eos at z=5.13. Together, the two events show that CCSNe at z>5 occur across a wide range of host environments, and AT 2026abck demonstrates that high-cadence blank-field JWST surveys can capture high-redshift SNe during their early, UV-bright phase.
ER  -

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