TITLE: GCN CIRCULAR NUMBER: 38926 SUBJECT: GRB 250101A: Terskol Zeiss-2000 optical observations DATE: 25/01/14 06:25:40 GMT FROM: Nicolai Pankov at HSE, IKI RAS colinsergesen@gmail.com

E. Mazaeva (IKI), N. Pankov (HSE, IKI), A. Pozanenko (IKI), N. Kapitanov (INASAN), A. Moskvitin (SAO RAS) report on behalf of the IKI-GRB-FuN collaboration:

We performed optical observations of the field of GRB 250101A (Page et. al, GCN 38752; Li et. al, GCN 38753; Mohan et. al, GCN 38754; Zhu et. al, GCN 38755; Budnev et. al, GCN 38756; Wu et. al, GCN 38758; Zhu et. al, GCN 38759; Goad et. al, GCN 38761; Moskvitin et. al, GCN 38762; Odeh et. al, GCN 38763; Hu et. al, GCN 38764; Moskvitin et. al, GCN 38765; D'Avino et. al, GCN 38768; Escudero-Coca et. al, GCN 38769; Leonini et. al, GCN 38771; Dichiara et. al, GCN 38773; Zhang et. al, GCN 38774; Siegel, GCN 38775; Li et. al, GCN 38776; Komesh et. al, GCN 38777; Ghosh et. al, GCN 38779; Moskvitin et al., GCN 38780; Krimm et. al, GCN 38782; Komesh et. al, GCN 38790; Méndez-Lapido et. al, GCN 38810; Gupta et. al, GCN 38818; Ferro et. al, GCN 38831; Lin et. al, GCN 38837; Pankov et. al., GCN 38869; Pankov et. al, GCN 38890) in the R filter with the 2-meter Zeiss-2000 telescope of the Terskol observatory starting on 2025-01-01 17:27 UT, i.e. ~4.8 hours since trigger. The preliminary photometry of the optical afterglow is as follows:

Date UT start t-T0 Exp. Filter OT Err. UL(3sigma) (mid, days) (s) 2025-01-01 17:27:31 0.19926 38*120 R 20.11 0.04 22.4 2025-01-01 21:37:20 0.35498 30*60 R 19.40 0.05 21.5 2025-01-02 14:57:45 1.07870 57*30 R 22.13 0.33 22.1 2025-01-02 21:44:44 1.35811 39*30 R 21.93 0.28 22.1 2025-01-03 18:02:09 2.22881 90*60 R n/d n/d 22.7

The photometry is based on nearby stars from the PS1 catalog (Lupton 2005 transformations). No correction has been made for the Galactic extinction. The obtained results confirm the re-brightening visible in other observations (Moskvitin et. al, GCN 38765; Pankov et. al, GCN 38890).

View this GCN Circular online at https://gcn.nasa.gov/circulars/38926. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...