TITLE: GCN CIRCULAR NUMBER: 36323 SUBJECT: EP240426a: YAHPT optical upper limit DATE: 24/04/26 16:57:35 GMT FROM: Tianrui Sun at Purple Mountain Obs,CAS trsun@pmo.ac.cn

Tian-Rui Sun, Jin-Jun Geng, Jian Chen, Yan-Long Hua and Lei Hu report on behalf of the YAHPT team:

Following the detection of EP240426a by Einstein Probe (Sun et al., GCN 36313), we use the Yaoan High Precision Telescope at Yaoan Astronomy Observation Station (Yunnan province, China) to search and follow up.

We observed the target position in both Rc and Ic starting from 2024-04-26T12:47:25.100 with 300s exposure. We did not detect any possible new optical counterpart with an uncertainty of 10 arcsec in the coadded image.

UT (start) |5 sigma Upper Limit| Exposure Time | Filter 2024-04-26T12:47:25.100| 21.26 | 300*8s | Rc 2024-04-26T12:42:22.700| 21.12 | 300*8s | Ic

This non-detection result of the transient is in agreement with the previous circulars (Wang et al., 36315; Xiong et al.,36320). We used the USNO B1.0 catalogue (R2mag and Imag) as the magnitude reference for calibration.

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