TITLE: GCN CIRCULAR NUMBER: 39884 SUBJECT: GRB 250327A: SVOM/VT optical candidate DATE: 25/03/27 16:42:22 GMT FROM: SVOM_group svomgroup@bao.ac.cn

L.P. Xin (NAOC), J. T. Palmerio (CEA), L. Zhang (IHEP), Y.D. Hu (GXU), X.L. Chen (YNU), Y. L. Qiu, H.L. Li., C. Wu, Z.H. Yao, Y.N. Ma, X.H. Han, H.B. Cai, J.Y. Wei (NAOC), B. Cordier (CEA), report on behalf of the SVOM/VT team:

SVOM performed a Target of Opportunity observation of GRB 250327A (Fermi GBM team, GCN 39876; Parsotan et al., GCN 39877). SVOM/VT began observing the field at 2025-03-27T11:25:40.50 UT, ~3.9 hours after the Swift/BAT trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.

An uncatalogued candidate is detected inside the Swift/BAT error circle at ra=248.18018, dec=61.63347 (J2000), corresponding to:

RA (J2000) = 16:32:43.2 Dec (J2000) = +61:38:00.5 with an uncertainty of 1.0 arcsec.

This source is not present in the archival Legacy Survey. The source is detected in the VT_R stacked image with exposure time of 47x60 seconds with VT_R = 22.8 +/- 0.3 mag (AB). The 3 sigma upper limit in the VT_B is 23.4 mag (AB).

We thank D.B. Malesani for helpful discussion.

The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC),CAS.

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