[vsnet-grb-info 1818] GRB050721A: optical decay

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3658
SUBJECT: GRB050721A: optical decay
DATE:    05/07/21 08:02:10 GMT
FROM:    Paolo D'Avanzo at INAF-OAB  <davanzo at merate.mi.astro.it>

P. D'Avanzo, S. Covino, (INAF/OABr), D. Malesani (SISSA), S. Bagnulo, T.
Szeifert (ESO), G. Tagliaferri (INAF/OABr), G. Chincarini (Univ. Milano-
Bicocca), S. Piranomonte, L.A. Antonelli, and L. Stella (INAF/OAR), on
behalf of the MISTICI collaboration, report:

We performed a preliminary analysis on our R-band images (Covino et al.,
GCN 3657) of the field of GRB050721 (Antonelli et al., GCN 3654).

The afterglow indicated by Torii (GCN 3655) and confirmed by Covino et
al. (GCN 3657) faded by ~ 0.9 mag in the R band between July 21.204 UT
and July 21.226 UT (25 and 56 minutes after the GRB respectively). This
implies a decay index of ~ 1.

At our last epoch, the afterglow magnitude was R ~ 18.6, with reference
to USNO star UO600_22128314 assumed to be R = 17.4

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