TITLE: GCN CIRCULAR NUMBER: 41158 SUBJECT: GRB 250725A: SVOM/VT optical candidate DATE: 25/07/25 09:38:16 GMT FROM: Huali Li at at NAOC, SVOM <lhl@nao.cas.cn> H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu, Z. H. Yao, Y. N. Ma, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. Palmerio (CEA), J. S. Deng, J. Y. Wei (NAOC), R. Z. Li (YNAO), X. L. Chen (YNU) report on behalf of the SVOM/VT team. SVOM performed a Target of Opportunity observation of GRB 250725A detected by Fermi/GBM (Fermi GBM Team, GCN 41150) and Swift/BAT (Evans et al., GCN 41152). SVOM/VT began observing the field at 2025-07-25 02:27:11 UTC, 36.1 min after the Swfit trigger time, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. An uncatalogued source compared to DESI catalogue, is found using VT X-band data, within the error box of Swift/XRT (Osborne et al., GCN 41153) at R.A., Dec 35.480401, -82.791125 degrees: RA (J2000) = 02:21:55.30 Dec (J2000) = -82:47:28.05 with an uncertainty of 0.5 arcsec. The source is detected in both VT_R and VT_B. It was fading in VT_R by 0.3 mag within about one hour during our observation. The AB magnitudes are: Mid time | exposure time | band | mag (AB) | mag err --------------------|-------------------|------|----------|-------- 0.93 hour | 70×13 sec | VT_B | 22.30 | 0.10 0.93 hour | 70×10 sec | VT_R | 19.33 | 0.02 Our measurements are not corrected for Galactic extinction. This source is proposed to be the optical candidate of the burst. Considerring the red color of VT_B-VT_R of about 2.9, the burst is supposed to be probable at medium/high redshift (Wang et al. 2020). The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/41158. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...