GCN Circular 39209
Subject
GRB 250207A: FRAM-Auger optical detection
Date
2025-02-07T17:00:05Z (15 days ago)
From
Martin Jelinek at Astro.Inst-AVCR,Ondrejov <martin.jelinek@asu.cas.cz>
Via
email
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.