TITLE: GCN CIRCULAR NUMBER: 39595 SUBJECT: GRB 250219A: SVOM/C-GFT optical upper limit at early phase DATE: 25/03/05 12:41:57 GMT FROM: SVOM_group svomgroup@bao.ac.cn

Zhe Kang (CHO), F. Daigne (IAP), M. Gnaoui (IAP), Liping Xin(NAOC), Xuhui Han(NAOC), Chao WU (NAOC), Pinpin Zhang (NAOC), Xiaomeng Lu (NAOC), Zhenwei Li (CHO), You Lv (CHO), Ruosong Zhang (NAOC), Yujie Xiao(NAOC), Yulei, Qiu(NAOC), Jing Wang(NAOC), Jianyan Wei (NAOC) report on behalf of the SVOM/C-GFT team:

We observed the field of GRB 250219A (SVOM/ECLAIRs burst-id:sb25021904, Daigne et al. GCN 39376) starting at 2025-02-19T16:03:29 UT, ~10.68 mins after the burst trigger with C-GFT. A series of g, r and i band images were obtained with exposure time of 10s for each frame. No source consistent with the XRT (Kennea et al., GCN 39379; Turpin et al., GCN 39456) was detected. The optical counterpart (Xin et al., GCN 39380; Magnani et al., GCN 39382; Fu et al., GCN 39383; ) was not detected in our images. The upper limit at early phase are,

(T-T0)_mid(sec) exptime(s) limiting_mag(3sigma) band ------------------------------------------------------ 678 6x10s >19.57 (6x10s) i 1013 6x10s >20.11 (6x10s) g 1102 6x10s >20.03 (6x10s) r

The photometry was calibrated with nearby stars in UCAC4 catalog. It is consistent with those results reported by Lagioia et al. (GCN 39381), Adami et al. (GCN 39384), Breeveld et al (GCN 39385), Turpin et al. (GCN 39407) and Komesh et al. (GCN 39419).

We thank the observation assistant Guangsheng Zhang and Chunlei Guo at Jilin observatory for their excellent support.

Chinese Ground Follow-up Telescope of SVOM mission is located at Jilin, Changchun Observatory, National Astronomical Observatories, CAS. It has FOV of 1.28 deg x 1.28 deg with a 4k*4k CMOS detector mounted on the primary focus of 1.2-meter-aperure telescope.

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