TITLE:   GCN CIRCULAR
NUMBER:  39654
SUBJECT: GRB 250309B / AT2025dws: KMTNet-CTIO optical observations
DATE:    25/03/10 16:46:17 GMT
FROM:    Min-Su Shin at Korea Astronomy and Space Science Institute <msshin@kasi.re.kr>

Min-Su Shin (Korea Astronomy and Space Science Institute; KASI),                 
Jae-Woo Kim (KASI), and Seo-Won Chang (Seoul National University)                
report on behalf of the KMTNet neutrino ToO program:                             
                                                                                 
We observed the area corresponding to the neutrino event IceCube-250309A         
with the KMTNet-CTIO for the initial coordinates of Zegarelli et. al, GCN 39631.  
                                                                                 
The KMTNet-CTIO observation started at 2025-03-09 09:44 (UTC), and               
we acquired I-band images for four pointings covering the entire                 
90% uncertainty area for the alert. The source AT2025dws 
(Stein et al., GCN 39639, Pérez-Fournon et al. GCN 39643,  
Moskvitin et al. GCN 39645, Perley et al. GCN 39646) 
is clearly found in the images with the following photometric measurements:

MJD          mag      err                                                                                                                       
60743.40574  17.88    0.02                                                                                                                      
60743.40723  17.87    0.02                                                                                                                      
                                                                                                                                                
We thank the KMTNet operators for their support.