TITLE:   GCN CIRCULAR
NUMBER:  39667
SUBJECT: GRB 250311A/EP250311a: TRT optical upper limit
DATE:    25/03/11 12:48:25 GMT
FROM:    Wenxiong Li at NAOC <liwenxiong1992@gmail.com>


W.X. Li (NAOC), S. Tinyanont, R. Anutarawiramkul, P. Butpan (NARIT), N.C. Sun, D. Xu, Z. Fan, Y.N. Wang (NAOC), report on behalf of a large collaboration:

We observed the field of GRB 250311A/EP250311a detected by MAXI (Tatano et al. GCN 39660) and EP (Mao et al., GCN 39664), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Sierra Remote Observatories in California. Observations started at 12:00:05 UT on 2025-03-11, i.e., ~10 hours after the EP trigger, and 2 x 300s frames were obtained in the R band.

No uncatalogued optical source is detected in the stacked R-band image within the EP/WXT error circle, down to the 3-sigma limiting magnitude of R ~ 20.