TITLE:   GCN CIRCULAR
NUMBER:  45852
SUBJECT: EP261006a: Early Optical Observations by WFST
DATE:    26/10/08 07:49:09 GMT
FROM:    Mingxin Wu at USTC <wmx112611226@mail.ustc.edu.cn>

Mingxin Wu (USTC), Ning Jiang (USTC), Zelin Xu (USTC), Linna Xu (USTC), Chengyi Wang (USTC), Jiazheng Zhu (USTC), Tinggui Wang (USTC), Ji-an Jiang (USTC) on behalf of the Wide Field Survey Telescope (WFST) team:

We report optical observations of the X-ray transient EP261006a (Lao et al., GCN [45826](https://gcn.nasa.gov/circulars/45826)) obtained with the Wide Field Survey Telescope (WFST) as part of its Wide Field Survey program.

Difference imaging reveals a clear optical counterpart within the EP-FXT localization, with an angular separation of less than 0.1 arcsec from the position of the galaxy Gaia DR3 2587044864659595392. Forced photometry on 2026-10-04 at 20:45:24 UT (g band) and 21:40:49 UT (r band), approximately two days before the X-ray detection, yields a non-detection with 3sigma upper limits of ~ 23 and 22 mag, respectively, indicating that the brightening is temporally coincident  with EP2611006a. Our detections on 2026-10-06 at 20:43:33 UT (r band) and 21:31:00 UT (u band) precede those reported by LT and NOT (Eyles-Ferris et al., GSN [45831](https://gcn.nasa.gov/circulars/45831)). Combining the WFST photometry with the LT and NOT measurements indicates a rising r-band light curve. The blue u-r color and nuclear location are consistent with the tentative classification as a TDE. 

We summarise our difference photometry below, where t0 denotes the EP/WXT trigger time (2026-10-06 at 17:49:57 UT).


| t_mid-t0 (hrs) | Filter |  AB magnitude  | Exposure time (s) |
| -------------- | ------ | -------------- | ----------------- |
|     −45.08     |   g    | > 23.15 (3σ)   |        30         |
|     −44.15     |   r    | > 22.40 (3σ)   |        30         |
|      2.89      |   r    | 20.42 ± 0.05   |        30         |
|      3.68      |   u    | 19.76 ± 0.05   |        30         |