TITLE: GCN CIRCULAR NUMBER: 37612 SUBJECT: GRB 240529A: FRAM-ORM early optical afterglow observations reveal plateau and rebrightening DATE: 24/09/26 15:18:39 GMT FROM: Martin Jelinek at Astro.Inst-AVCR,Ondrejov martin.jelinek@asu.cas.cz
Martin Jelinek, Alzbeta Malenakova, Jan Strobl (ASU CAS Ondrejov, CZ), Sergey Karpov, Martin Masek, Petr Janecek, Jakub Jurysek, Jan Ebr, Ronan Cunniffe, Petr Travnicek and Michael Prouza (Institute of Physics, Prague, CZ)
report:
The 25cm robotic telescope FRAM-ORM at La Palma (Spain) responded automatically to the Swift alert of GRB 240529A (Eyles-Ferris et al., GCN 36556; Osborne et al., GCN 36557; Dichiara et al., GCN 36564; Markwardt et al., GCN 36566). We obtained a series of unfiltered 20s and 60s exposures starting at 02:59:07.8 UT, (37s post-trigger) and covering two hours of the afterglow evolution.
Due to an ongoing focusing run at the time of the alert, initial frames were out of focus. Nevertheless, the optical afterglow was clearly detected in all focused and defocused images, allowing for a comprehensive early-time light curve from an early plateau through initial decay to the start of a substantial rebrightening.
Combining our data with published measurements (Dutton et al., GCN 36568; Mo et al., GCN 36569), we reconstruct the overall light curve behavior:
a) Initial plateau: The afterglow maintained a nearly constant brightness, declining marginally from r~15.2 to 15.5 during the first 2ks post-trigger.
b) Gradual decay: The initial plateau gradually transitioned to a decay with the decay index consistent with the later decay.
c) Rebrightening: The trend reverses suddenly at ~4.2ks and the afterglow nearly reaches its initial brightness at a second peak of r~15.8 at t~10ks.
d) Final decay: after 10ks, the afterglow decays with a power-law index alpha ~ 1.85, consistent with multiple team reports (Kumar et al., GCN 36559; Fu et al., GCN 36561; Shilling et al., GCN 36562; Perez-Garcia et al., GCN 36563; Dutton et al., GCN 36568; Mo et al., GCN 36569)
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