TITLE: GCN CIRCULAR NUMBER: 38807 SUBJECT: GRB 250103A: TSHAO optical upper limit DATE: 25/01/03 22:04:21 GMT FROM: Alexei Pozanenko at IKI, Moscow grb.alex@gmail.com

I. Reva (FAI), A. Pozanenko (IKI), A. Volnova (IKI), N. Pankov (HSE, IKI) report on behalf of GRB IKI FuN:

We observed the field of GRB 250103A (Wang et al., GCN 38786) which also triggered GBM/Fermi (Trigg et al., GCN 38806) with Zeiss-1000 telescope of THSAO observatory in R-filter starting on 2025-01-03 (UT) 16:12:14.05. In a stacked image we do not detect the optical afterglow (Li et al., GCN 38795; SVOM/VT commissioning team, GCN 38802), and which is consistent with non detection of the afterglow (SVOM/C-GFT team, GCN 38791; Starling et al., GCN 38792). Preliminary photometry of the field is the following

Date UT start t-T0 Filter Exp. OT Err UL(3sigma) mid, days 2025-01-03 16:12:14 0.26231 R 11*120 n/d n/d 19.0

The photometry is based on nearby USNO-B1.0 (R2) stars.

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