TITLE: GCN CIRCULAR NUMBER: 39836 SUBJECT: EP250321a: Mondy AZT-33IK Optical Observations DATE: 25/03/22 17:46:10 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 EP250321a (Hu et. al, GCN 39800; Page et. al, GCN 39811, Hu et. al, GCN 39833) at the redshift of z = 4.368 (Zhu 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) 2025-03-21 16:42:58, i.e. about 0.46 days since trigger. The optical afterglow (Fu et. al, GCN 39804; Perez-Garcia et. al, GCN 39805; Brivio et. al, GCN 39807; Zhu et. al, GCN 39809; Becerra et. al, GCN 39810; Pérez-Fournon et. al, GCN 39812; Lee et. al, GCN 39815; Han et. al, GCN 39817; Jin et. al, GCN 39822; Zhu et. al, GCN 39827; Gill et. al, GCN 39831; Zheng et. al, GCN ) is detected in the stacked image. The preliminary photometry is as follows:
Date UT start t-T0 Exp. Filter OT Err UL(3sigma) (mid, days) (s) 2025-03-21 16:42:58 0.46042 30*120 R 22.41 0.28 22.8
The photometry is based on nearby stars of SDSS-DR12 and has not been corrected for the Galactic extinction.
SDSS-DR12 RA Dec R(Lupton transformations, 2005) 179.2552 +17.3825 18.123 +/- 0.049 179.2436 +17.3713 18.846 +/- 0.012
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