TITLE:   GCN CIRCULAR
NUMBER:  33559
SUBJECT: GRB 230328B: Multa observatory optical afterglow observation
DATE:    23/04/03 23:51:33 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

N. Pankov (HSE), L. Elenin (KIAM RAS), A. Krylov (KIAM RAS), A. 
Pozanenko (IKI), S. Belkin (IKI) report on behalf of GRB IKI FuN:

We observed  the field of GRB 230328B (Gropp et al. GCN 33527; Veres et 
al., GCN 33526; Dalessi et al., GCN 33531; Waratkar et al., GCN 33532; 
Dafcikova  et al., GCN 33543; Svinkin  et al. GCN  33544) with 
Santel-400 (0.4m) telescope of ISON-Multa observatory (Altay Republic) 
in  Clear filter on 2023-03-28 starting on (UT) 15:16:06. We detect the 
optical afterglow of GRB 230328B (Gropp et al. GCN 33527; Pankov et al. 
GCN 33528; Belkin et al. GCN 33530; Lu et al. GCN 33534; Catapano et al. 
GCN  33535; Suresh et al. GCN 33536; Adami  et al. GCN 33537; Gompertz 
et al. GCN 33538; Komesh  et al. GCN 33539; Lu et al. GCN 33540; Ror et 
al. GCN 33547; Kugel  et al. GCN 33550; Siegel et al. GCN 33556).

Preliminary photometry  of the afterglow source is following

Date        UT start  t-T0    Exp.  Filter   OT    Err.  UL(3sigma)
                    (mid, days) (s)

2023-03-28  15:16:06 0.04603  90*60 Clear    18.9  0.1   20.0

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