EP241021a as An Off-nuclear Month-duration Transient in a Dwarf Starburst Galaxy
Abstract
EP241021a is a peculiar fast X-ray transient exhibiting a long X-ray plateau and an optical rebrightening, both challenging the traditional jet afterglow model. Whether its nature is a stellar explosion or a tidal disruption event (TDE) remains debated. Here we present late-time HST/WFC3 and Gemini-N/GMOS observations of its host galaxy at z=0.748. After ∼300 days post-trigger, the transient emission had faded below detection, revealing a dwarf disk galaxy with an effective radius Re=1.7 kpc, a stellar mass M⋆∼3×108M⊙, and a high star formation rate of ∼5 M⊙ yr−1. Combined with previous very long baseline interferometry measurements, the transient can be located in the galactic disk with a projected physical offset of 0.95±0.13 kpc from the galaxy center. Host-subtracted optical light curves show that the rebrightening ceased at ∼47 days, followed by a sudden drop with a power-law index steeper than −3.3, coincident with a similar drop in the X-ray light curve. This synchronous drop in both bands is consistent with jet shut-off, and the required month-long jet activity suggests a persistently accreting compact object fed by a TDE. Among the TDE scenarios, the off-nuclear location and the starburst host galaxy slightly favor the post-supernova micro-TDE scenario in a binary system, in which a natal kick drives the newborn compact object into a tidal disruption of its companion. Nevertheless, an off-nuclear intermediate-mass black hole TDE or a stellar-mass black hole TDE induced by dynamical scattering in a dense stellar cluster cannot yet be excluded.
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BibTeX
@misc{sun2026ep241021a,
title = {{EP241021a as An Off-nuclear Month-duration Transient in a Dwarf Starburst Galaxy}},
author = {Luming Sun and Xinwen Shu and Jiazheng Zhu and Ning Jiang and Bing Zhang and Jin-Hong Chen and Lixin Dai and Hucheng Ding and Chichuan Jin and Wenbin Lu and Rong-Feng Shen and Fan Xu and Lei Yang and Yunwei Yu and Weimin Yuan and Dongyue Li and Dong Xu and Tinggui Wang and Haonan Yang and Wenda Zhang},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.34217},
eprint = {2610.34217},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.34217},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - EP241021a as An Off-nuclear Month-duration Transient in a Dwarf Starburst Galaxy
AU - Luming Sun
AU - Xinwen Shu
AU - Jiazheng Zhu
AU - Ning Jiang
AU - Bing Zhang
AU - Jin-Hong Chen
AU - Lixin Dai
AU - Hucheng Ding
AU - Chichuan Jin
AU - Wenbin Lu
AU - Rong-Feng Shen
AU - Fan Xu
AU - Lei Yang
AU - Yunwei Yu
AU - Weimin Yuan
AU - Dongyue Li
AU - Dong Xu
AU - Tinggui Wang
AU - Haonan Yang
AU - Wenda Zhang
PY - 2026
DA - 2026/10/25
PB - arXiv
DO - 10.48550/arxiv.2610.34217
UR - https://arxiv.org/abs/2610.34217
AB - EP241021a is a peculiar fast X-ray transient exhibiting a long X-ray plateau and an optical rebrightening, both challenging the traditional jet afterglow model. Whether its nature is a stellar explosion or a tidal disruption event (TDE) remains debated. Here we present late-time HST/WFC3 and Gemini-N/GMOS observations of its host galaxy at z=0.748. After ∼300 days post-trigger, the transient emission had faded below detection, revealing a dwarf disk galaxy with an effective radius R_e=1.7 kpc, a stellar mass M_⋆∼3×10^8M_⊙, and a high star formation rate of ∼5 M_⊙ yr^−1. Combined with previous very long baseline interferometry measurements, the transient can be located in the galactic disk with a projected physical offset of 0.95±0.13 kpc from the galaxy center. Host-subtracted optical light curves show that the rebrightening ceased at ∼47 days, followed by a sudden drop with a power-law index steeper than −3.3, coincident with a similar drop in the X-ray light curve. This synchronous drop in both bands is consistent with jet shut-off, and the required month-long jet activity suggests a persistently accreting compact object fed by a TDE. Among the TDE scenarios, the off-nuclear location and the starburst host galaxy slightly favor the post-supernova micro-TDE scenario in a binary system, in which a natal kick drives the newborn compact object into a tidal disruption of its companion. Nevertheless, an off-nuclear intermediate-mass black hole TDE or a stellar-mass black hole TDE induced by dynamical scattering in a dense stellar cluster cannot yet be excluded.
ER -