TITLE: GCN CIRCULAR NUMBER: 40789 SUBJECT: GRB 250617B: Nickel telescope optical observations DATE: 25/06/20 00:49:40 GMT FROM: Weikang Zheng at UC Berkeley weikang@berkeley.edu

Eli Gendreau-Distler, Gracelynn Jost, William Wu, WeiKang Zheng and

Alex Filippenko (UC Berkeley) report on behalf of the KAIT GRB team:

We observed the field of GRB 250617B (Page et. al, GCN 40760; The

Fermi GBM team, GCN 40763) with the 1-m Nickel telescope located at

Lick observatory, California. Observations were performed in R band

with 600s x 5 exposure time started at 09:46 UT on June 18. We

clearly detected the optical afterglow (Page et. al, GCN 40760,

Moskvitin et. al, GCN 40761, Jelinek et. al, GCN 40762; Kumar et. al,

GCN 40768; Lipunov et. al, GCN 40769; Grossan et. al, GCN 40771;

Ma et. al, GCN 40772; Schneider et. al, GCN 40774; Antier et. al,

GCN 40775; Corcoran et. al, GCN 40776; Turpin et. al, GCN 40777;

Siegel & Page, GCN 40778; Pankov et al., GCN 40783) in our coadd image

with 21.4 +/- 0.1 mag at a mid time of 13.10 hours after the burst.

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