TITLE: GCN CIRCULAR NUMBER: 38396 SUBJECT: LIGO/Virgo/KAGRA S241125n: GRANDMA Optical Upper Limits DATE: 24/11/30 17:57:41 GMT FROM: Dalya Akl at American Uni. SHJ <dalyaakl.d@gmail.com> D. Akl (AUS), C. Andrade (UMN), E. de Bruin (UMN), M. Tanasan (NARIT), N. Kochiashvili (AbAO), T. Hussenot-Desenonges (IJCLAB), M. Coughlin (UMN), M. Molham (NRIAG), S. Agayeva (Shamakhy Obs.), S. Antier (OCA), S. Karpov (FZU), D. Turpin (CEA-Saclay/Irfu), I. Tosta e Melo (UniCT-DFA), P. Hello (IJCLAB), P-A Duverne (APC), T. Pradier (Unistra/IPHC), N. Guessoum (AUS), M. Masek (FZU), K. Noysena (NARIT), M. Eldepsy (NRIAG), A. Shokry (NRIAG), E. Elhosseiny (NRIAG), A. Takey (NRIAG) on behalf of the GRANDMA collaboration: We observed the field of the Swift/BAT-GUANO candidate counterpart (DeLaunay et al., GCN 38308) of the GW compact binary merger candidate S241125n (LIGO/Virgo/KAGRA Collaborations, GCN 38305) with the GRANDMA network. Our observations were conducted with the FRAM-CTA-N, TRT-SRO, and KAO telescopes starting ~0.8 days post T0 in the R, I, and i' bands, respectively. No clear candidate is identified within the 5 arcmin uncertainty region around the BAT position (RA, Dec = 58.079, 69.689 deg), with the following 5-sigma upperlimits: +---------------------+-------------+--------+----------+------------+ | T-mid(UTC) | Exposure(s) | Filter | U.L.(AB) | Instrument | +=====================+=============+========+==========+============+ | 2024-11-25T20:32:50 | 20x120 | R | 16.38 | FRAM-CTA-N | | 2024-11-25T23:38:47 | 23x150 | i' | 21.87 | KAO | | 2024-11-27T07:30:28 | 6x300 | I | 19.83 | TRT-SRO | | 2024-11-28T02:35:43 | 8x300 | I | 20.22 | TRT-SRO | +---------------------+-------------+--------+----------+------------+ This non-detection is consistent with Chen et al., GCN 38314, Watson et al., GCN 38317, Swain et al., GCN 38322, Mohan et al., GCN 38325, Jiang et al., GCN 38328, Becerra et al., GCN 38329. Our FRAM-CTA-N observation includes the positions of all 5 Swift-XRT X-ray sources (Page et al., GCN 38324). The KAO and TRT-SRO observations include only the position of the S241125n_X3 XRT source. We do not detect any clear candidates within the localization regions of these sources. This non-detection is consistent with Becerra et al., GCN 38329 and Akl et al., GCN 38334. Further, the FRAM-CTA-N observation includes all of the X-ray sources detected by EP-FXT (Wang et al., GCN 38345), while the KAO and TRT-SRO images include only the X-ray source detected by both modules of the EP-FXT with an averaged position at RA, Dec = 58.1097, 69.6392 deg and an uncertainty of 10 arcsec. We do not detect any of the EP-FXT sources across all of our images. All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained in Johnson Cousin filters were calibrated using the Gaia DR3 Synphot catalog, while images taken with Sloan filters were calibrated using the Pan-STARRS DR1 catalog. We use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023). GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). View this GCN Circular online at https://gcn.nasa.gov/circulars/38396. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...