GCN Circular 41953
Subject
GRB 250920B: CrAO ZTSH optical observations
Event
Date
2025-09-23T12:38:45Z (5 months ago)
From
Nicolai Pankov at HSE, IKI RAS <colinsergesen@gmail.com>
Via
Web form
N. Pankov (HSE, IKI), A. Pozanenko (IKI), A. Moskvitin (SAO RAS), V. Rumyantsev (CrAO) report on behalf of GRB-IKI-FuN:
We observed the field of a long GRB 250920B detected by Fermi/GBM (The Fermi GBM team GCN 41897), Swift (Gupta et. al, GCN 41898), with the ZTSH telescope of CrAO. We obtained series of images in R,V bands starting on 2025-09-21 at 16:28:47.74 UT, i.e. 1.321 days since Fermi/GBM trigger. The optical afterglow initially detected by Swift/UVOT (Gupta et. al, GCN 41898) and further observed by (WU et. al, GCN 41908; Hall et. al, GCN 41914; Pankov et. al, GCN 41931; Reguitti et. al, GCN 41932; Moskvitin et. al, GCN 41948) is clearly visible in individual 120 s exposures taken in the R-band. Preliminary photometry of the OT in the R-band is as follows:
Date UTstart Exptime t-T0 Filter OT Err. UL
(s) (mid, days) (3sigma)
2025-09-21 17:21:58 120 1.35870 R 20.7 0.1 22
The photometry was calibrated against nearby USNO-B1.0 stars (R2 mags) and not corrected for the Galactic extinction.