TITLE:   GCN CIRCULAR
NUMBER:  39444
SUBJECT: LIGO/Virgo/KAGRA S250223dk: DDOTI Upper Limits on the Optical Counterpart
DATE:    25/02/24 04:53:21 GMT
FROM:    Alan Watson at UNAM <alan@astro.unam.mx>

Alan M. Watson (UNAM), William H. Lee (UNAM), Océlotl López (UNAM), Camila Angulo Valdez (UNAM), Rosa L. Becerra (U Roma), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), and Margarita Pereyra (UNAM), and Eleonora Troja (U Roma) report:

We imaged the field of the Swift/BAT-GUANO trigger possibly associated with LIGO/Virgo/KAGRA S250223dk (GCN Circ. 39443) with the DDOTI wide-field imager at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico (http://ddoti.astroscu.unam.mx).

We observed the whole BAT error region from 2025-02-24 03:56 UTC to 04:24 UTC (15.9 to 16.4 hours after the GW event) at extremely high airmass. We obtained a total exposure of 24 minutes.

Comparing our observations to the USNO-B1 and PanSTARRS PS1 DR2 catalogues, we detect no uncatalogued sources within the observed BAT error region to a 5-sigma AB limiting magnitude of 

w > 20.0.

Our photometry is in the AB system and is not corrected for Galactic extinction.

We thank the staff of the Observatorio Astronómico Nacional in San Pedro Mártir.