TITLE: GCN CIRCULAR NUMBER: 39772 SUBJECT: GRB 250317B: Mondy AZT-33IK Optical Observations DATE: 25/03/18 15:19:56 GMT FROM: Nicolai Pankov at HSE, IKI RAS colinsergesen@gmail.com
N. Pankov (HSE, IKI), E. Klunko (ISTP), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN:
We performed optical observations of the field of GRB 250317B (Zhao et. al, GCN 39753; Götz et. al, GCN 39756; Melandri et. al, GCN 39763) at the redshift of z=3.44 (Thoene et. al, GCN 39769) in the R filter with the 1.5-meter AZT-33IK telescope of the Sayan Solar Observatory (Mondy). The observations started on (UT) 2025-03-17 15:41:49, i.e. about 0.58 days since trigger. The optical afterglow (Watson et. al, GCN 39754; Pérez-Fournon et. al, GCN 39757; Ghosh et. al, GCN 39759; Ferro et. al, GCN 39764; Schneider et. al, GCN 39767; Thoene et. al, GCN 39769; Zhu et. al, GCN 39770) is clearly visible in the stacked image. The preliminary photometry is as follows:
Date UT start t-T0 Exp. Filter OT Err UL(3sigma) (mid, days) (s) 2025-03-17 15:41:49 0.58173 28*120 R 20.88 0.13 22.8
Ref. stars from SDSS-DR12 RA Dec R R_err 211.6590 +40.0703 16.451 0.029 211.5997 +40.0619 18.859 0.055
The photometry is based on nearby stars (see the list above) from the SDSS-DR12 catalog (R magnitudes were obtained using Lupton 2005 transformations) and has not been corrected for the Galactic extinction. Using a simple power law fit to the observed data in the r and R filters, we estimate the light curve decay index to be about -1.5.
View this GCN Circular online at https://gcn.nasa.gov/circulars/39772. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...