TITLE: GCN CIRCULAR NUMBER: 37292 SUBJECT: GRB 240825A: SVOM/C-GFT optical observations DATE: 24/08/26 03:35:03 GMT FROM: Chao Wu at NAOC wuchao.lamost@gmail.com

SVOM/C-GFT team: 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)

SVOM JSWG: Jian-Yan Wei (NAOC, China), Bertrand Cordier (CEA, F), Shuang-Nan Zhang (IHEP, CN), Stephane Basa (LAM, F), Jean-Luc Attéia (IRAP, F), Arnaud Claret (CEA, F), Zi-Gao Dai (USTC, CN), Frederic Daigne (IAP, F), Jin-Song Deng (NAOC, CN), Andrea Goldwurm (APC, F), Diego Götz (CEA, F), Xu-Hui Han (NAOC, CN), Cyril Lachaud (APC, F), En-Wei Liang (GXU, CN), Yu-Lei Qiu (NAOC, CN), Susanna Vergani (Obs.Paris, F), Jing Wang (NAOC, CN), Chao Wu(NAOC, CN), Li-Ping Xin (NAOC,CN), Bing Zhang (UNLV, CN)

We observed the burst GRB 240525A (Swift trigger 1250617, Gupta et al., GCN 37274; Fermi/GBM trigger 746293985.085054 / 240825662, GCN 37273) on 15:54:05 UT, Aug. 25, 2024, about 65 seconds after the Swift trigger with C-GFT (Chinese Ground Follow-up Telescope in SVOM mission) in System Test Mode (STM). C-GFT is located at Jilin (long.=126.33 deg, lat.=43.8243778 deg), 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.

A series of g,r and i band images were obtained. The exposure time was 10 seconds for each frame. The optical optical afterglow reported (Jiang et al., GCN 37275; Dutton et al., GCN 37276; Odeh et al., GCN 37277; Zhang et al., GCN 37278; Li et al., GCN 37280; Izzo et al., GCN 37287, Lipunov GCN 37289, Leonini GCN 37291) are clearly detected in our images. The preliminary photometric results are listed as following, ----------------------------------------------------------- Filter (t-T0) sec mag +/- mag_error g 65 -> 2555 14.56 +/- 0.02 -> 19.18 +/- 0.20 r 206 -> 2088 14.56 +/- 0.02 -> 19.33 +/- 0.15 i 294 -> 2162 16.79 +/- 0.02 -> 19.33 +/- 0.15

The photometry was calibrated with nearby PS1 catalogs. More detailed analysis is continuing.

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

The SVOM/C-GFT point of contact for this burst is: Chao Wu (cwu@bao.ac.cn)

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