TITLE: GCN CIRCULAR NUMBER: 39209 SUBJECT: GRB 250207A: FRAM-Auger optical detection DATE: 25/02/07 17:00:05 GMT FROM: Martin Jelinek at Astro.Inst-AVCR,Ondrejov martin.jelinek@asu.cas.cz
Martin Jelinek (ASU CAS Ondrejov, CZ), Martin Masek, Petr Janecek, Sergey Karpov, Jakub Jurysek, Jan Ebr, Ronan Cunniffe, Petr Travnicek, Michael Prouza (Institute of Physics, Prague, CZ) and Jan Strobl (ASU CAS Ondrejov, CZ) report:
The 30cm robotic telescope FRAM-Auger in Malargue (Argentina) reacted robotically to the Swift/BAT and Fermi/GBM alert of GRB250207A (Fermi GBM Team, GCN 39181; Ferro et al., GCN 39182), starting with a series of 20s R-band images at 01:16:49 UT, i.e. 42s post trigger.
We detect the optical afterglow at the position reported by Brivio et al. (GCN 39202), Kuin & Ferro (GCN 39199), and Angulo et al. (GCN 39186) in our initial frames. The early light curve shows a relatively steep decay with a power-law index alpha ~ 1.6. Extrapolation of this decay rate appears inconsistent with later observations by COLIBRI (Angulo et al., GCN 39186), suggesting a possible transition in the light curve slope beyond ~600s post burst.
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