GCN Circular 7857
Subject
GRB 080605: optical observations
Event
Date
2008-06-07T19:42:52Z (18 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
V. Rumyantsev (CrAO), A. Pozanenko (IKI) report on behalf of larger GRB
follow-up collaboration:
We observed the optical afterglow of Swift GRB 080605 (Sbarufatti et al.,
GCN 7828) in second epoch on June 06 with Zeiss-1000 (Simeiz) telescope of
CrAO observatory with favorable weather conditions and seeing about 2". Our
first epoch astrometry of the source (Rumyantsev et al., GCN 7833) is in
agreement with refined UVOT position of GRB080605 (Kuin et al., GCN 7844).
The observation of the first epoch started 8 minute after burst onset
(Rumyantsev et al., GCN 7833) was performed under descending weather
conditions with seeing about 3". Improved photometry of the first epoch
observation as well as observation on June 6 is based on USNO-B1.0 star RA
(J2000) = 17 28 29.92, Dec.(J2000) = +04 00 36.5, assuming R=15.90, I=14.54:
T0+ Exposure, Filter, mag,
(d,mid time)
0.006251 120 R 18.04 +/- 0.08
0.007698 120 R 18.43 +/- 0.06
0.009457 120 R 18.62 +/- 0.06
0.010985 120 R 18.63 +/- 0.23
0.015163 120 R 18.93 +/- 0.23
0.018068 120 R >19.04
0.019504 120 R 18.86 +/- 0.20
0.026031 120 I 18.12 +/- 0.28
0.033219 120 V >17.50
0.034654 120 V >18.20
0.904028 34x120 R 21.13 +/- 0.06
The photometry is still preliminary and not corrected for Galaxy extinction
and might be affected by the bright, nearby star.
It is evident that the source is faded between June 5 and June 6. Power law
index of early afterglow decay ~0.8 is compatible with index obtained in
I-band (Kann et al., GCN 7845). However our absolute photometry in R-band
have a significant offset in comparison with early observations by Kann et
al. (GCN 7845) and compatible with photometry of Gomboc et al. (GCN 7831).
Our early observation suggests R-I ~ 1.2, however we caution the color of
the afterglow is also depending on photometry which is affected by bright,
nearby star.
The message may be cited.