GCN Circular 41930
Subject
GRB 250917B: Mondy and Zeiss-1000 SAO RAS optical observations, optical observations, afterglow candidate
Event
Date
2025-09-21T13:38:53Z (6 months ago)
From
Alexei Pozanenko at IKI, Moscow <grb.alex@gmail.com>
Via
email
N. Pankov (HSE), A. Pozanenko (IKI), A. Moskvitin (SAO RAS), E. Klunko
(ISTP), O. Spiridonova (SAO RAS) report on behalf of GRB IKI FuN:
We observed the field of Swift XRT of GRB 250917B (Fermi GBM team GCN
41846; Caputo et al. GCN 41848 ) with AZT-33IK telescope of Mondy
observatory in R-filter on 2025-09-17 starting (UT) 13:36:18(epoch 1) and
Zeiss-1000 of SAO RAS starting on 2025-09-17 (UT) 16:24:04 (epoch 2).
We do not detect any new sources within S1, S5, S6 XRT localisation (Kennea
et al., GCN 41851). This is consistent with optical observations (Hu et al,
GCN 41854; Breeveld et al, GCN 41864; Yadav et al., GCN 41872; Zheng et
al., GCN 41927).
However, at the boundary of the S5 XRT circle, we found an object
(coordinates are (J2000) 19:25:33.74 +11:04:24.85) that was significantly
brighter in epoch 1 compared to epoch 2. The photometry of the object is
the following
Date UT start t-T0 Filter OT Err. UL(3sigma) Telescope
(mid, days) (s)
2025-09-17 13:36:18 0.31845 R 19.97 +/- 0.08 21.4 AZT-33IK
2025-09-17 16:24:04 0.42394 Rc 20.79 +/- 0.12 21.3 Zeiss-1000
We suggest the source is an afterglow candidate of GRB 250917B.
The object is a diffuse one and most likely is the galaxy.