GCN Circular 40971
Subject
EP250704a / GRB 250704B: NOT observations of the optical afterglow
Event
Date
2025-07-05T11:11:01Z (3 months ago)
From
Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk>
Via
Web form
A. Martin-Carrillo (UCD), D. B. Malesani (DAWN/NBI and Radboud), X. Liu (NAOC), A. K. Haris-Kiss (Helsinki Univ.), M. Korpi-Lagg (Aalto Univ.), S. Wedemeyer (Univ. Oslo), A. Casasbuenas Corral (IAC), report on behalf of a larger collaboration:
We observed the field of the EP250704a (Li et al., GCN 40941) also detected by SVOM (GRB 250704B; Wang et al., GCN 40940), using the StanCam camera mounted on the Nordic Optical Telescope (NOT). We obtained 6x300 s exposures in the i band, starting at 2025-07-05 at 00:03:42.7 UT (15.78 hr after the EP trigger).
The optical afterglow detected by COLIBRÍ (Schneider et al., GCN 40942), BOOTES-5 (Perez-Garcia et al., GCN 40957), Pan-STARRS (Gillanders et al., GCN 40958), SVOM/VT (Xin et al., GCN 40960), GROWTH-India (Mohan et al., GCN 40962), SAO RAS (Moskvitin et al., GCN 40963), JinShan (Liu et al., GCN 40965), VLT/X-shooter (An et al., GCN 40966), and VLT/HAWK-I (Yang et al., GCN 40970) is well visible in all individual images with a magnitude
i = 19.78 +/- 0.05 (AB),
calibrated against nearby Pan-STARRS sources and not corrected for Galactic extinction.
Our i-band magnitude suggests a possible re-brightening when compared to the value reported by Liu et al. (GCN 40958), recorded about 10.29 hr after the trigger, and in general confirms the flat, and unusual, behavior of the early optical light curve.