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. 

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|Date|		|JD start|	|t-T0 (hours)|	|Exp (sec)|	|Filter|	|Magnitude| 
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2025-04-27	2460793.48177	19.91		2 x 600 	r		r = 19.05 +/- 0.07
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The field was calibrated against nearby APASS stars, with magnitudes converted using Lupton (2005) equations, and has not been corrected for Galactic extinction.