TITLE: GCN CIRCULAR NUMBER: 37363 SUBJECT: GRB 240828B: AbAO optical upper limit DATE: 24/08/31 16:13:21 GMT FROM: Alexei Pozanenko at IKI, Moscow grb.alex@gmail.com

S. Belkin (HSE, IKI), R. Ya. Inasaridze (AbAO), A. Pozanenko (IKI), N. Pankov (HSE, IKI) report on behalf of GRB-IKI-FuN:

We observed the field of GRB 240828B (Le Provost, GCN 37318; Page et al., GCN 37334) with the 70-cm AS-32 telescope of Abastumani Observatory (AbAO) in the R-filter, starting on 2024-08-29 at 23:38:46 (UT). We did not detect the optical counterpart in the stacked image within the Swift-XRT error circle (Page et al., GCN 37334; ). Preliminary photometry is as follows:

Date UT_start t-T0 Filter Exp. OT err UL(3σ) (mid, days) (s) 2024-08-29 23:38:46 1.46045 R 74×60 n/d n/d 22.0

The magnitudes were calibrated using nearby USNO-B1.0 stars. RA DEC R2 04:13:38.682 +16:40:58.242 17.00 04:13:51.313 +16:42:50.073 16.7

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