[vsnet-grb-info 9924] GRB 101024A: Zadko observatory - Gingin. Optical observations refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  11382
SUBJECT: GRB 101024A: Zadko observatory - Gingin. Optical observations refined analysis
DATE:    10/10/26 08:46:02 GMT
FROM:    Myrtille LAAS-BOUREZ at U.Western Australia  <myrtille.laas at oamp.fr>

GRB 101024A: Zadko observatory - Gingin. Optical observations refined
analysis
-------------------------------------------------------------------------------
M. Laas-Bourez (UWA/ICRAR), A. Klotz (CESR-UPS-CNRS), D. Coward (UWA),
D. Blair (UWA),
M. Boer (OHP-CNRS), P. Thierry (CESR-UPS-CNRS) report:

We analyzed carefully early images of GRB101024A
taken with the Zadko telescope, Gingin, Australia
(see Laas-Bourez et al. 2010 GCNC 11380). Images
are unfiltered. Magnitudes are converted into R
band using the star NOMAD1 0127-0023961 R=13.61
supposing (V-R)=0.6 for the optical counterpart
of the GRB. Magnitudes are not corrected for galactic
dust extinction.

-------------------------------
start end   Rmag
(s)   (s)
-------------------------------
215   222  16.55 +/-0.15
222   245  16.72 +/-0.15
259   289  16.86 +/-0.12
305   335  17.06 +/-0.12
349   379  17.24 +/-0.12
394   424  17.23 +/-0.12
-------------------------------

Considering a law decay in flux proportional to
t^-alpha, there is a consistent decrease with
alpha ~ 1.1 between 215 and ~ 360 seconds.
After 360 seconds, a plateau seems to be reached
lasting at least 60 seconds.

Compared to the UVOT data taken in the same range
of time (De Pasquale et al. 2010 GCNC 11375) the
optical afterglow is very red, consistent with a
redshift z>2.

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