TITLE:   GCN CIRCULAR
NUMBER:  40049
SUBJECT: GRB 250402A: Mondy optical observations
DATE:    25/04/04 14:24:06 GMT
FROM:    Alexei Pozanenko at IKI, Moscow <grb.alex@gmail.com>

E. Mazaeva (IKI), E. Klunko (ISTP), N. Pankov (HSE), A. Pozanenko (IKI)
report on behalf of IKI GRB-FuN:

We observed GRB 250402A (Chen et al. GCN 40014) with the AZT-33IK telescope
starting on 2025-04-03 (UT) 18:11:28. We found the optical counterpart (Xin
et al., GCN 40015; Pérez-Fournon et al., GCN 40020; Schneider et al., GCN
40022; Magnani et al., GCN 40023) at the position reported by Xin et al.,
GCN 40015.

Preliminary photometry of the optical counterpart is the following

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

2025-04-03 18:11:28 0.81567 R 29*120 21.9 0.2 22.3

The photometry is based on the nearby PS1 stars (R mag by Lupton
transformations).