TITLE: GCN CIRCULAR NUMBER: 41236 SUBJECT: GRB 250805A: TRT optical upper limits DATE: 25/08/05 08:56:31 GMT FROM: liuxing@nao.cas.cn

X. Liu (NAOC), K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), L.B. He, Z.P. Zhu, S.Q. Jiang, J. An, D. Xu (NAOC), S.Y. Fu (HUST) report on behalf of a large collaboration:

We observed the field of GRB 250805A (Ambrosi et al, GCN 41233), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Cerro Tololo Inter-American Observatory, Chile. Observations started at 06:27:50.5 UTC on 2025-08-05, i.e., ~ 0.3 hr after the Swift/BAT trigger, and 10 x 200 s frames were obtained in the Sloan r- and i- bands.

No new optical source is detected in the co-added r- and i-band images within the Swift/XRT error circle (Kennea et al, GCN 41234). The limiting magnitudes are as follow:

| Tmid(s) | band | upper limit(3sigma) | | :-----: | :--: | :-----------------: | | 2746.99 | i | 20.7 | | 3545.62 | r | 20.8 |

The magnitudes are calibrated against Legacy Survey DR10 and are not corrected for Galactic extinction.

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