TITLE:   GCN CIRCULAR
NUMBER:  37500
SUBJECT: EP240913a: JinShan optical upper limits
DATE:    24/09/14 11:31:29 GMT
FROM:    Dong Xu at NAOC/CAS <dxu@nao.cas.cn>

Z.P. Zhu, S.Y. Fu, S.Q. Jiang, J. An, X. Liu, D. Xu (NAOC), J.Z. Liu (XAO) report on behalf of a large collaboration:

We observed the field of EP240913a detected by Einstein Probe (EP, Li et al., GCN 37492), using the 100cm-C telescope (100C) of the JinShan project, located at Altay, Xinjiang, China. Observations started at 16:48:02 UT on 2024-09-13, i.e., 5.1 hr after the EP trigger, and a series of frames were obtained in the Sloan r- and z-bands.

No new optical source is detected within the error circle of the proposed X-ray counterpart (Jiang et al., GCN 37497), down to the following 5-sigma upper limits:

T_mid (UT) | T_mid (hr) | filter | Exposue|5-sigma U.L. (AB)
2024-09-13T17:59:25 | 6.331 | r | 13x200s +10x300s | 21.9
2024-09-13T17:29:08 | 5.827 | z | 9x200s           | 19.3

calibrated with nearby PanSTARRS stars and not corrected for Galactic extinction.

We acknowledge the excellent support from X. Yao, S.W. Luo, and Z.K. Feng for enabling these observations.