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arXiv · 2512.11572

JWST and HST observations of the host galaxy and supernova, SN 2024aihh in EP240801a at z=1.67

Agnes P. C. van Hoof·Andrew J. Levan·Peter G. Jonker·Morgan Fraser·Luca Izzo·Andrew S. Fruchter·Joyce N. D. van Dalen·Nial R. Tanvir·Jens Hjorth·Antonio Martin-Carrillo·Nikhil Sarin·Laura C. Cotter·Jonathan A. Quirola-Vásquez·Maria E. Ravasio·Javi Sánchez-Sierras·Manuel A. P. Torres·Shuai-Qing Jiang·Dong Xu
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Abstract

We present James Webb Space Telescope (JWST) and Hubble Space Telescope (HST) observations of the counterpart of EP240801a, at z=1.67, the first fast X-ray transient (FXT) identified as an X-ray flash (XRF) by the Einstein Probe (EP) and Fermi-GBM. Our observations reveal strong photometric and spectroscopic evidence for an associated broad-lined Type Ic supernova (SN) SN 2024aihh, the most distant spectroscopically identified gamma ray-burst (GRB)-SN to date. The SN exhibits similar luminosity and light curve evolution to the proto-type GRB-SN 1998bw with an absolute magnitude of the SN at $\sim$23 days rest-frame of $M_{F140W} \approx$-19 mag. The SN is located in a host galaxy with complex morphology at a large ($\sim$6 kpc) offset in a region of relatively low surface brightness. The region around the SN has a modest star formation rate and is dominated by an intermediate mass-weighted age (1.4$\pm$0.3 Gyr) population, despite the apparent presence of a young, massive broad-lined Type Ic SN progenitor. These observations demonstrate that observations with HST and JWST can greatly extend the redshift range over which the GRB/FXT-SN connection can be studied, including in relatively low luminosity, X-ray rich events. They demonstrate little apparent evolution in the SN properties from local examples despite EP240801a originating from an epoch 10 Gyr ago.

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Agnes P. C. van Hoof, Andrew J. Levan, Peter G. Jonker, Morgan Fraser, Luca Izzo, Andrew S. Fruchter, Joyce N. D. van Dalen, Nial R. Tanvir, Jens Hjorth, Antonio Martin-Carrillo, Nikhil Sarin, Laura C. Cotter, Jonathan A. Quirola-Vásquez, Maria E. Ravasio, Javi Sánchez-Sierras, Manuel A. P. Torres, Shuai-Qing Jiang, Dong Xu. 2025-12-12. JWST and HST observations of the host galaxy and supernova, SN 2024aihh in EP240801a at z=1.67. https://arxiv.org/abs/2512.11572

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