TITLE: GCN CIRCULAR NUMBER: 39911 SUBJECT: GRB 250328A: GWAC-F50A optical upper limit DATE: 25/03/28 17:58:43 GMT FROM: Liping Xin at NAOC, SVOM xlp@nao.cas.cn

L. P. Xin(NAOC), Y. G. Yang(HNU), X. H. Han, C. WU, Y. L. Qiu, J. Wang, H. L. Li, X .M. Lu, R. S. Zhang, Y. Xu, L. Huang, H. B. Cai, Y. J. Xiao, P. P. Zhang, L. Lan, W. J. Xie, Z. H. Yao, J. Y. Wei(NAOC), X. G. Wang, E. W. Liang(GXU) report on behalf of the SVOM/F50A team:

We began to observe GRB 250328A (Brunet et al., GCN 39910) with 50cm telescope (GWAC-F50A) at Xinglong station, China, at 2025-03-28T16:59:19 (UT), about 145s after the burst.

With the first observations with exposure time of 6*100 sec, no any uncatalogued source was detected in our stacked image down to a 3 sigma limit magnitude of 19.0 mag in R band, at the mid time of 7.5 min after the burst, comparing to several nearby USNO B1.0 stars.

We acknowledge the excellent support from observation assistant Yangtong Zheng and Winlong Dong.

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