[vsnet-grb-info 7939] GRB090529: Further NOT optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9482
SUBJECT: GRB090529: Further NOT optical observations
DATE:    09/06/02 21:57:20 GMT
FROM:    Dong Xu at DARK,NBI  <dong at astro.ku.dk>

D. Xu, G. Leloudas, D. Malesani, J. P. U. Fynbo, J. Maund (DARK/NBI), P. 
Jakobsson (Univ. Iceland), and T. Liimets (NOT & Tartu Obs.) report on 
behalf of a larger collaboration:

We continued to observe the field of GRB 090529 (Sakamoto et al., GCN 
9430) with the Nordic Optical Telescope equipped with ALFOSC.  We 
obtained 3x600 s R-band frames staring on June 01, 21:26:31 UT and 
ending on June 01, 22:00:52 UT. The mid-exposure time is 3.31 days after 
the burst.

The optical afterglow (Xin et al., GCN 9431; Schady et al., GCN 9435) is 
still detected in the stacked frame. Using the same reference star as in 
  Kann et al. (GCN 9436) and in Leloudas et al. (GCN 9453), we obtain 
R=22.8+/-0.1 for the afterglow.

Measurements by Kann et al. (0.3 day after the burst) and Leloudas et 
al. (1.29 days after the burst) indicate an optical power-law decay 
index of alpha1=0.72. Our new observation indicates that the optical 
decay became even slower, with an index of alpha2=0.3 between our two 
obs epochs. In contrast, during the whole period of 0.3 - 3.31 days the 
X-ray afterglow decays with the index of ~1.0 (ref, Evans et al. 2009). 
The slow optical decay may be also due to the presence of a fairly 
bright host galaxy.

Further optical observations are encouraged.