GCN Circular 41643
Xander J. Hall (CMU), Lei Hu (CMU), Tomás Cabrera (CMU), Brendan O’Connor (CMU), Antonella Palmese (CMU), Igor Andreoni (UNC), James Freeburn (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 2025-09-01T03:39 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 new transients within the LVK 99% CI area, and we report here select transients of high quality and interest:
First, one matched to a NED galaxy within the 90% volume (GCN 41608):
| id | AT name | ra | dec | discovery_date (UT) | mag_g | mag_g_err | mag_g-mag_i | NED separation |
|---|---|---|---|---|---|---|---|---|
| T202509012137497m775946 | AT 2025wpv | 324.457179 | -77.996131 | 2025-09-01 03:57:43.776 | 22.6 | 0.3 | 1.16 | 1.6” |
Next, a transient of a known Gaia quasar (Gavras et al. 2023):
| id | AT name | ra | dec | discovery_date (UT) | mag_g | mag_g_err | mag_g-mag_i | Gaia separation |
|---|---|---|---|---|---|---|---|---|
| A202509012159035m780432 | AT 2025wpq | 329.764660 | -78.075678 | 2025-09-01 03:41:20.544 | 20.3 | 0.3 | 0.6 | 0.165” |
Finally, we confirm the transient reported by McMahon et al. (GCN 41640):
| id | AT name | ra | dec | discovery_date (UT) | mag_g | mag_g_err | mag_g-mag_i |
|---|---|---|---|---|---|---|---|
| T202509012157542m772445 | AT 2025wpk | 329.475736 | -77.412522 | 2025-09-01 03:49:33.024 | 22.2 | 0.2 | 1.2 |
Further analysis is underway.
We thank the CTIO and NOIRLab staff for supporting these observations and the data calibration.