TITLE: GCN CIRCULAR NUMBER: 40264 SUBJECT: EP250427a: REM optical/NIR afterglow detection DATE: 25/04/27 13:23:16 GMT FROM: Riccardo Brivio at INAF-OAB riccardo.brivio@inaf.it
R. Brivio, M. Ferro, P. D’Avanzo, S. Covino, D. Fugazza (INAF-OAB) report on behalf of the REM team:
We observed the field of EP250427a detected by EP/WXT (Wang et al., GCN 40257), also seen by Fermi/GBM (Ravasio et al., GCN 40262) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the g, r, i, z, J, H, and K bands, started on 2025 April 27 at 07:20:13 UT (i.e. 3.7 h after the burst).
From preliminary photometry, we detect the optical/NIR counterpart (Perez-Garcia et al., GCN 40259; Liu et al., GCN 40260; Becerra et al., GCN 40261) with the following magnitudes:
r = 18.1 +/- 0.3 (AB; calibrated against the Pan-STARRS catalogue), at a mid-time of 3.7 h after the trigger,
H = 15.3 +/- 0.2 (Vega; calibrated against the 2MASS catalogue), at a mid-time of 3.7 h after the trigger,
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