TITLE: GCN CIRCULAR NUMBER: 40360 SUBJECT: GRB 250506A: TRT optical observations DATE: 25/05/06 09:28:48 GMT FROM: Dong Xu at NAOC/CAS <dxu@nao.cas.cn> X. Liu (NAOC), K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), S.Y. Fu (HUST), Z.P. Zhu, S.Q. Jiang, J. An, D. Xu (NAOC) report on behalf of a large collaboration: We observed the field of GRB 250506A detected by SVOM/ECLAIRs (Wang et al., GCN 40358) and probably by Fermi/GBM as well (Fermi GBM team, GCN 40355), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Cerro Tololo Inter-American Observatory, Chile. Within the Swift/XRT error circle (https://www.swift.ac.uk/SVOM/SVOM_FIELD00014/), a brightening, catalogued, and seemingly round source is detected at coordinates R.A. (J2000) = 14:38:34.03 Dec. (J2000) = +29:13:02.10 which has r = 18.41+/- 0.01 in the TRT image (calibrated with PanSTARRS) at a median time of 4.48 hrs after the SVOM trigger, while it has has r = 19.00 +/- 0.01 mag in PanSTARRS. This source is also covered by SDSS, Legacy Survey, and GAIA. In GAIA, it is classified as a QSO. The source has a photometric redshift of z ~ 0.46+/-0.10 from SDSS and z ~ 0.49+/-0.26 from Legacy Survey. No new source is detected within the Swift/XRT error circle, down to a limiting magnitude of r ~ 21.8 mag. View this GCN Circular online at https://gcn.nasa.gov/circulars/40360. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...