TITLE: GCN CIRCULAR NUMBER: 40293 SUBJECT: EP 250427A: Optical counterpart detection by LCO. DATE: 25/04/30 18:45:08 GMT FROM: ankur ghosh at CAPP, University of Johannesburg ghosh.ankur1994@gmail.com

Ankur Ghosh, Soebur Razzaque (CAPP, University of Johannesburg), Alexander Moskvitin, Yulia Sotnikova (SAO RAS), Naveen Dukiya (ARIES), Rahul Gupta (NASA GSFC) on behalf of a larger collaboration.

We observed the field of the EP 250427A triggered by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission and Fermi (Wang et al. GCN 40257, Ravasio et al. GCN 40262) in the r filter of the 0.4 m SCICAM QHY600 at the Las Cumbres Observatory Global Telescope (LCOGT) node located at South African Astronomical Observatory (SAAO). The 0.4 m SCICAM QHY600 is equipped with 9576 x 6388 pixel CCD (FOV: 1.9 x 1.2 degrees, scale: 0.74 arcsec/pixel) but we only used the FOV of 30 x 30 arcmin for our observation.

Observations began on April 27, 2025, starting 19.90 hours after the GRB trigger.

We clearly detect the optical transient (OT) reported by GCNs (Perez-Garcia et al., GCN #40259), TRT (Liu et al., GCN #40260), COLIBRÍ (Becerra et al., GCN #40261), REM (Brivio et al., GCN #40264), LCO (Pérez-Fournon et al., GCN #40267), LT (Qiang Xi et al., GCN #40269), GIT (Swain et al., GCN #40270), COLIBRÍ (Magnani et al., GCN #40271), Lesedi (S. de Wet et al., GCN #40272), FTW (Busmann et al., GCN #40273), OHP/T193 (Amram et al., GCN #40275, Amram et al., GCN #40288, Eappachen et al., GCN #40289) in our r band image.

------------------------------------------------------------------------------------------------------ |Date| |JD start| |t-T0 (hours)| |Exp (sec)| |Filter| |Magnitude| ------------------------------------------------------------------------------------------------------ 2025-04-27 2460793.48177 19.91 2 x 600 r r = 19.05 +/- 0.07 ------------------------------------------------------------------------------------------------------

The field was calibrated against nearby APASS stars, with magnitudes converted using Lupton (2005) equations, and has not been corrected for Galactic extinction.

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