TITLE: GCN CIRCULAR NUMBER: 39226 SUBJECT: LIGO/Virgo/KAGRA S250206dm: COLIBRÍ/DDRAGO Observations of the DDOTI optical candidates DATE: 25/02/08 06:55:31 GMT FROM: F. Fortin at IRAP ffortin.sci.edu@gmail.com

Francis Fortin (IRAP), Alan M. Watson (UNAM), Sarah Antier (OCA), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Jean-Luc Atteia (IRAP), Rosa L. Becerra (Università degli Studi di Roma Tor Vergata), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Noémie Globus (UNAM), Francesco Magnani (CPPM), Margarita Pereyra (UNAM), and Benjamin Schneider (LAM) report:

We imaged the fields of the two candidates reported by the DDOTI team (Becerra et al., GCN Circ. 39208) as a possible optical counterpart of the GW transient S250206dm (LVK Collaboration, GCN Circ. 39175, GCN Circ. 39184) with the DDRAGO wide-field imager on the COLIBRÍ telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico.

We observed source 1 from 2025-02-08 04:48 to 05:20, obtaining 480 seconds of exposure in each of the g and r filters. At the position of the source reported by Becerra et al., we do not detect a source to 3-sigma limiting magnitudes of:

g > 22.0 r > 22.1

We observed source 2 from 2025-02-08 05:39 to 06:09, again obtaining 480 seconds of exposure in each of the g and r filters. At the position of the source reported by Becerra et al., we do not detect a source to 3-sigma limiting magnitudes of:

g > 22.5 r > 22.6

The data were reduced and stacked using custom software and then calibrated against the PS1 catalog and analysed using STDPipe (Karpov 2021).

Our magnitude limits are not corrected for Galactic extinction.

Our limits at about 32 hours after the GW event are significantly fainter than the detections reported by the DDOTI team.

We warmly thank the COLIBRÍ and DDRAGO engineering teams and the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir.

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