TITLE: GCN CIRCULAR NUMBER: 41741 SUBJECT: LIGO/Virgo/KAGRA S250830bp: DECam/SOAR GW-MMADS updates DATE: 25/09/06 17:01:35 GMT FROM: Xander J Hall at Carnegie Mellon University <xjh@andrew.cmu.edu> Xander J. Hall (CMU), Lei Hu (CMU), Tomás Cabrera (CMU), James Freeburn (UNC), Antonella Palmese (CMU), Brendan O’Connor (CMU), Igor Andreoni (UNC), Keerthi Kunnumkai (CMU), on behalf of the Gravitational Wave MultiMessenger Astronomy DECam Survey (GW-MMADS) team report: DECam observed the high probability area of the LVK gravitational wave candidate S250830bp (GCN 41606) using the wide-field Dark Energy Camera (DECam) on the 4m Blanco telescope. Observations started at 2025-09-05T04:12:03 UTC (Prop ID: 2025B-485252; PI Soares-Santos) and covered the highest 90% probability region of the event (GCN 41607). We run the SFFT difference imaging (Hu et al. 2022) on the available images, filter out likely stars and moving objects, and then visually inspect the remaining transients. We report on TNS 13 newly identified transients within the LVK 99% CI area. We report the new transient AT 2025xab as a likely supernova and note that none of our nuclear transients show any compelling evolution. A crossmatch with Gaia reveals AT 2025wzv and AT 2025wzw (McMahon et al. GCN 41739) as galactic sources, thus we conclude these are not associated with S250830bp (GCN 41607). We also provide updates on previously announced candidates: We report that AT 2025wpk has shown little to no color evolution or brightness change since its last observation and that AT 2025wpv has shown a slow decline in brightness, dropping ~0.1 mag/day. Finally, we report on AT 2025wpq (GCN 41643), which was observed by SOAR at 2025-09-04T05:32:07 UTC (PI Andreoni). We clearly see broad Halpha and Hbeta securing its classification as a quasar at a z ~ 0.4, thus, we therefore conclude this candidate is far too distant to be associated with S250830bp (GCN 41607). Further analysis is underway. We thank the CTIO and NOIRLab staff for supporting these observations and the data calibration. View this GCN Circular online at https://gcn.nasa.gov/circulars/41741. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...