TITLE: GCN CIRCULAR NUMBER: 39983 SUBJECT: GRB 250329B: CAHA 2.2m telescope optical limit DATE: 25/03/31 18:52:11 GMT FROM: Youdong HU at INAF-OAB huyoudong072@hotmail.com

A. J. Castro-Tirado, E. Fernandez-Garcia, I. Perez-Garcia, S.-Y. Wu, M. D. Caballero-Garcia, R. Sanchez-Ramirez, S. Guziy (IAA-CSIC), Y.-D. Hu (GXU), and A. Fernandez-Martin, J. F. Agui Fernandez (CAHA) on behalf of a larger collaboration, report:

Following the detection of GRB 250329B by SVOM/ECLAIRs (Xie et al. GCNC 39925), we triggered the 2.2m CAHA telescope (+ CAFOS) at the Calar Alto Observatory (Almeria, Spain). Images were gathered starting on Mar. 30 01:33:35 UT (i.e. ~13.4 hours after trigger) in Sloan-riz and clear bands for the error region. On the co-added z band image (90 x 10 s), no optical transient detected, includeing the afterglow detected by Swift/XRT (Beardmore et al. GCNC 39939, P. Evans GCNC 39971), which down to 22.5 mag. This non-detection is consistent with the reports from GWAC-F50A (Xin et al. GCNC 39926), Mephisto (Chen et al. GCNC 39929), SVOM/VT (Xin et al. GCNC 39931), SVOM/C-GFT (Wu et al. GCNC 39935), SVOM/F-GFT (Rakotondrainibe et al. GCNC 39945).

We thank the staff at Calar Alto observatory for their excellent support.

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