TITLE:   GCN CIRCULAR
NUMBER:  40245
SUBJECT: GRB 250419A: Mondy Optical Observations
DATE:    25/04/25 07:34:22 GMT
FROM:    Nicolai Pankov at HSE, IKI RAS <colinsergesen@gmail.com>

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

We continued observations of the field of GRB 250419A (Wang et al., GCN 40168; Page et al., GCN 40111; Page et al., GCN 40176) at the redshift of z = 0.845 (Thakur et al., GCN 40174) with the 1.5-meter AZT-33IK telescope of the Sayan Solar Observatory (Mondy). The R-band observations began on 2025-04-22 at 17:29:31 UT, i.e. ~3.65 days since trigger. The field of the optical counterpart was observed by (López et al., GCN 40169; Xin et al., GCN 40170; Zheng et al., GCN 40171; Kumar et al., GCN 40172; Thakur et al., GCN 40174; Lipunov et al., GCN 40179; Odeh et al., GCN 40180; Perley & Bochenek, GCN 40181; Pankov et al., GCN 40182; Pérez-Fournon et al., GCN 40183; Kuin, GCN 40185; Wu et al., GCN 40186; Xie et al., GCN 40187; Jiang et al., GCN 40188; Ghosh et al., GCN 40189; Bochenek & Perley, GCN 40190; Pankov et. al, GCN 40202; Masi, GCN GCN 40206; Calapai, GCN 40209; Lagioia et al., GCN 40210; Dimple & Gompertz, GCN 40238; Bochenek & Perley, GCN 40239). We detect the OT in the stacked image. The preliminary photometry is as follows:

Date       UTstart  Exptime     t-T0     Filter OT    Err     UL   
                      (s)   (mid, days)                    (3sigma)
2025-04-22 17:29:31 45*120     3.65625      R   21.83 0.15   22.5    

The photometry is based on nearby USNO-B1.0 stars (R2 magnitudes, provided in Pankov et al., GCN 40182) and has not been corrected for the Galactic extinction.