WFST Follow-up of S251112cm: Searching for an Optical Counterpart to a Subsolar-mass Compact-binary Merger Candidate

@article{liu2026wfst,
  title = {{WFST Follow-up of S251112cm: Searching for an Optical Counterpart to a Subsolar-mass Compact-binary Merger Candidate}},
  author = {Zhengyan Liu and Zelin Xu and Ji-an Jiang and Wen Zhao and Zhiping Jin and Zigao Dai and Dezheng Meng and Yefei Yuan and Xuefeng Wu and Lulu Fan and Xu Kong and Xander J. Hall and Antonella Palmese and Feng Li and Ming Liang and Binyang Liu and Zhen Wan and Hairen Wang and Jian Wang and Tinggui Wang and Hongfei Zhang and Xianzhong Zheng and Qingfeng Zhu},
  journal = {The Astrophysical Journal Letters},
  year = {2026},
  month = nov,
  doi = {10.3847/2041-8213/aeb6bf},
  url = {https://iopscience.iop.org/article/10.3847/2041-8213/aeb6bf},
  note = {CC BY 4.0},
}

TY  - JOUR
TI  - WFST Follow-up of S251112cm: Searching for an Optical Counterpart to a Subsolar-mass Compact-binary Merger Candidate
AU  - Zhengyan Liu
AU  - Zelin Xu
AU  - Ji-an Jiang
AU  - Wen Zhao
AU  - Zhiping Jin
AU  - Zigao Dai
AU  - Dezheng Meng
AU  - Yefei Yuan
AU  - Xuefeng Wu
AU  - Lulu Fan
AU  - Xu Kong
AU  - Xander J. Hall
AU  - Antonella Palmese
AU  - Feng Li
AU  - Ming Liang
AU  - Binyang Liu
AU  - Zhen Wan
AU  - Hairen Wang
AU  - Jian Wang
AU  - Tinggui Wang
AU  - Hongfei Zhang
AU  - Xianzhong Zheng
AU  - Qingfeng Zhu
PY  - 2026
DA  - 2026/11/05
JO  - The Astrophysical Journal Letters
DO  - 10.3847/2041-8213/aeb6bf
UR  - https://iopscience.iop.org/article/10.3847/2041-8213/aeb6bf
AB  - Electromagnetic counterparts to gravitational-wave (GW) sources probe the properties, environments, and evolution of compact-object mergers. S251112cm belongs to an emerging class of GW candidates with possible subsolar-mass components. We present an optical counterpart search for S251112cm with the Wide Field Survey Telescope (WFST). The observations began 20.2 hr after the GW trigger and continued for 3 nights, covering approximately 780 deg ² and 51% of the localization probability in the updated skymap. We searched for newly emerging, rapidly evolving, off-nuclear optical transients and identified four candidates whose host-galaxy distances are broadly consistent with the GW distance estimate. However, all four evolve substantially more slowly than AT 2017gfo, ruling out an AT 2017gfo-like origin and disfavoring their association with S251112cm as rapidly evolving kilonova counterparts. Combining WFST and DECam observations increases the covered localization probability to approximately 67%. Conditional on the counterpart lying within this footprint, we constrain a grid of binary-neutron-star kilonova models. For viewing angles θ obs < 60 ∘ , with the other parameters fixed to the best-fitting values for AT 2017gfo, models with dynamical ejecta mass M dyn ≳ 0.01 M ⊙ or wind ejecta mass M wind ≳ 0.05 M ⊙ are disfavored over most of the covered GW probability. Beyond kilonova models, our phenomenological analysis constrains rapidly evolving optical transients with T rise,1/2 ≤ 2 days to peak absolute magnitudes fainter than approximately −13 mag. To our knowledge, WFST provides the strongest optical constraints to date in the northern sky on possible rapidly evolving counterparts to this new class of GW candidates involving subsolar-mass compact objects. The comparable depths and complementary sky coverage of WFST and DECam extend these constraints across a larger fraction of the localization region at similar sensitivity.
SN  - 2041-8213
SN  - 2041-8205
ER  -