TITLE: GCN CIRCULAR NUMBER: 39827 SUBJECT: EP250321a: WFST optical observations DATE: 25/03/22 02:51:05 GMT FROM: Jin-Jun Geng at PMO jjgeng@pmo.ac.cn

Jia-Zheng Zhu, Jin-Jun Geng, Ze-Lin Xu, Ning Jiang, Yan-Long Hua, Yi-Fang Liang, Ding-Fang Hu, Ji-An Jiang, Xue-Feng Wu, and Tian-Rui Sun report on behalf of the WFST team:

Following the detection of EP250321a by Einstein Probe (Hu et al., GCN 39800), we use the Wide Field Survey Telescope (WFST Collaboration; arXiv:2306.07590) at Lenghu Astronomical Observation Base (Qinghai province, China) to search and follow up its afterglow. We observed the target position with 3x120s exposure in r-band starting from 2025-03-21T14:17:14.

We clearly detect the optical transient (OT) reported by GCNs (Fu et al., GCN 39804; Perez-Garcia et al al., GCN 39805; Brivio et al., GCN 39807; Zhu et al., GCN 39809; Becerra et al., GCN 39810; Pérez-Fournon et al., GCN 39812; Lee et al., GCN 39815; Ghosh et al., GCN 39816; Han et al., GCN 39817; Jin et al., GCN 39822) in our image. Our preliminary results are as follows:

|Date| |UTstart| |t-T0 (hours)| |Exp (sec)| |Filter| |Magnitude| ---------------------------------------------------------------------------------------------- 2025-03-21 14:17:14 8.12 3 x 120 r 22.57 +/- 0.12

We thank the WFST staff for supporting these observations.

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