TITLE: GCN CIRCULAR NUMBER: 41216 SUBJECT: LIGO/Virgo/KAGRA S250727dc: GRANDMA/OPD observations of AT2025smm DATE: 25/08/01 22:47:59 GMT FROM: Nelio Sasaki at NEPA-UEA nsasaki@uea.edu.br

Wagner Corradi (LNA), Nélio Sasaki (UEA-Parintins), Leandro de Almeida (LNA), Felipe Navarete (LNA), S. Antier (OCA/IJCLAB), Yodgor Rajabov (UBAI), Yusufjion Tillayev (UBAI), Eslam Elhosseiny (NRIAG), C. Andrade (UMN), D. Turpin (CEA), I. Tosta e Melo (IFN), M. Coughlin (UMN), P. Hello (IJCLAB), P-A. Duverne (APC), S. Karpov (FZU) and T. Pradier (IPHC) on behalf of Observatório do Pico dos Dias (OPD/LNA/Brazil) and the GRANDMA collaboration, we inspected the optical candidate AT2025smm (GCNs 41179) of the gravitational-wave event  S250727dc (GCNs 41179, 41487), reported by Swift/UVOT (GCN 41179,GCN 41187, GCN 41188, GCN 41196, GCN 41197, GCN 41201, GCN 41202, GCN 41205, GCN 41211 and GCN 41214). Observations were conducted with the 0.6 m telescope at OPD, obtaining six frames of 300s exposures in the Bessel-R band between 2025-07-31T08:18:35.268  and 2025-07-31T08:48:35.268 UTC. No source is detected at the reported position in the stacked image. The final stacked frame covers a field of view of 11.6′ × 11.6′ with a pixel scale of 0.34″ arcsecond per pixel. Here we report the following limiting magnitudes, uncorrected for Galactic extinction: Filter | Mag (AB) r | > 22.53 This result is in agreement with the analysis of DECam GW-MMADS (GCN 41197). We use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023). GRANDMA is a worldwide telescope network (http://grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518).

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