TITLE: GCN CIRCULAR NUMBER: 40211 SUBJECT: IceCube-250421A: DDOTI Detection of the LAST Candidate DATE: 25/04/22 19:03:39 GMT FROM: sahil.atri@students.uniroma2.eu

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

We observe the field of the IceCube-250421A (bronze) event with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on the Sierra of San Pedro Martir (http://ddoti.astroscu.unam.mx) on the night of 2025-04-22 UTC.

DDOTI automatically pointed to the region centred in RA, Dec (J2000)= 16:03:46.49 +28:43:50.8, covering about 96% of the IceCube error region. DDOTI observed from 04:50 UTC to 11:47 UTC (from T+ 11.74 h to T+ 18.69 h after the trigger) with a total exposure of 3.5 hours, alternating with other scientific programs.

Comparing our observations to the USNO-B1 and PanSTARRS PS1 DR2 catalogues, we detect the candidate reported by SN 2025cbj at w=18.53+/0.04, consistent with the observations from the Large Array Survey Telescope (Garrappa et al., GCN Circ. 40208).

No other uncatalogued sources within the observed field to an average 10-sigma limiting AB magnitude of:

w > 20.7

This value is not corrected for the Galactic extinction.

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

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