[vsnet-grb-info 3808] GRB 060927: Early color

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  5642
SUBJECT: GRB 060927: Early color
DATE:    06/09/28 03:53:36 GMT
FROM:    Ken ichi Torii at Osaka U  <torii at ess.sci.osaka-u.ac.jp>

K. Torii (Osaka U.) reports on behalf of the ART collaboration:

 As we reported in GCN 5630, the error region of GRB 060927 (Barbier
et al. GCN 5627) was observed with the 14 inch ART-3a (from 53 s after
the burst in Ic band) and 0.35m ART-3b (from 112 s after the burst in
Rc band) simultaneously.

 The optical afterglow (Schaefer et al. GCN 5629) was detected in the
Ic band frames (Ic ~ 16.0 in the first 60 s exposure), but it was not
detected in single Rc band frames.

 Combining our measurements and those reported in the circulars
 (GCN 5629; Zhai et al. GCN 5638), we roughly estimate the early Rc-Ic
color redder (larger) than 1.5 and probably Rc-Ic ~ 2.0 at 100 s after
the trigger time. This early color is consistent with that derived
from later measurements at t ~ 300-1200 s (Guidorzi et al. GCN 5633;
Sarugaku et al. GCN 5634; GCN 5638). The non detection in the UVOT
white filter (GCN 5629) also suggests that the afterglow was red at t ~
100 s.

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