TITLE: GCN CIRCULAR NUMBER: 40842 SUBJECT: GRB 250625A: SVOM/C-GFT upper limit in early phase DATE: 25/06/26 15:29:45 GMT FROM: SVOM_group svomgroup@bao.ac.cn
Chao WU (NAOC), Zhe Kang (CHO), Liping Xin(NAOC), Xuhui Han(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), Jinsong Deng(NAOC), Lei Huang(NAOC), Jianyan Wei (NAOC), report on behalf of the SVOM/C-GFT team:
We observed the field of GRB 250625A detected by Swift-BAT（Ferro et al., GCN 40825) and Fermi-GBM (GCN 40824) with LATIOS on SVOM/C-GFT. Observations started at 2025-06-25T16:06:18 UTC, ~82 seconds after the trigger.
A series of g, r, and i band images were obtained. The optical afterglow reported by Moskvitin et al. (GCN 40828), Xin et al. (GCN 40830), Zhu et al. (GCN 40834), Fortin et al. (GCN 40837), Adami et al. (GCN 40838) and Brosio et al. (GCN 40839) is not detected in the images after preliminary processing. The three sigma upper limits are:
| date-obs|mid-time | exposure time (s) | band | upper limit (AB) | |--------------------|-------------------|------|-------------------| |2025-06-25T16:08:18 | 170 | i | 20.00 | |2025-06-25T16:27:53 | 180 | g | 20.59 | |2025-06-25T16:31:28 | 180 | r | 20.52 |
The photometry was calibrated with nearby UCAC4 catalogue. This result is consistent with the report by Breeveld & Ferro (GCN 40840).
We thank the observation assistants Chunlei Guo and Shuai Liu at Jilin observatory for their excellent support.
The Chinese Ground Follow-up Telescope (C-GFT) for the SVOM mission is located at Jilin Station, Changchun Observatory, National Astronomical Observatories, CAS. It features two instruments: (1) CATCH at the Cassegrain focus with a 21 arcsec x 21 arcsec FOV for simultaneous g/r/i-band imaging, and (2) LATIOS, a 4k x 4k CMOS camera at the prime focus with a 1.28 deg x 1.28 deg FOV that images in g, r, and i bands via filter switching.
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