TITLE: GCN CIRCULAR NUMBER: 38901 SUBJECT: GRB 250109A / EP250109a: Terskol (INASAN) and SAO RAS observations DATE: 25/01/10 22:51:16 GMT FROM: Moskvitin Alexander at SAO RAS mosk@sao.ru

A. Moskvitin, O. Spiridonova (SAO), A. Pozanenko (IKI), N. Kapitanov (INASAN), N. Pankov (IKI, HSE) report on behalf of larger GRB follow-up GRB IKI FuN collaboration.

We observed the field of the GRB 250109A / EP250109a (Li et al., GCN 38864; Fermi GBM team, GCN 38873) with two telescopes, 2-m Zeiss-2000 of Terskol observatory and 1-m Zeiss-1000 of SAO RAS on January 9. We obtained 100 x 60 sec. images R band on Jan. 09, 19:36:42--21:28:07 UT with 2-m telescope and 11 x 300 sec. images in Rc band on Jan. 09, 21:12:33--22:23:56 UT with 1-m telescope.

In the stacked image of Zeiss-2000 observation we marginally detect the afterglow candidate (Qiu et al., GCN 38872) within XRT error circle (Kennea et al., GCN 38899). Photometry of the staked images is the following:

Date UT start t-T0, h(mid) Filter Exp.,s OT, err, UL(3sigma) Telescope 25-01-09 19:36:42 14.254 R 100 x 60 22.5 0.4 22.4 Zeiss-2000 25-01-09 21:12:33 15.518 Rc 11 x 300 n/d n/d 22.2 Zeiss-1000

The photometry is based on nearby stars of the PS1 catalog (Lupton 2005 transformations) and not corrected for the Galactic extinction.

View this GCN Circular online at https://gcn.nasa.gov/circulars/38901. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...