TITLE: GCN CIRCULAR NUMBER: 41355 SUBJECT: GRB 250813B: Ondrejov D50 fast decay DATE: 25/08/14 00:46:58 GMT FROM: Martin Jelinek at Astro.Inst-AVCR,Ondrejov martin.jelinek@asu.cas.cz

M. Jelinek, J. Strobl, F. Novotny, R. Hudec (ASU CAS Ondrejov) report:

Further to our earlier report (GCN 41353), we provide refined photometric analysis of the optical afterglow of GRB 250813B (Xie et al., GCN 41352).

Our photometry reveals an extremely rapid decay with the afterglow fading from the initial magnitude of ~14.4 at ~100s post-trigger to near magnitude 20 at 0.03 days (43 minutes) after the trigger. This represents a fade of approximately 5.6 magnitudes in less than one hour and an average decay rate of ~1.8.

Potential observers should note the rapid evolution when planning follow-up observations.

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