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GCN Circular 9488

GRB 090530: Further NOT optical observations
2009-06-03T19:51:39Z (15 years ago)
Dong Xu at DARK,NBI <>
D. Xu, G. Leloudas, D. Malesani, J. P. U. Fynbo, J. Hjorth (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 090530 (Cannizzo et al., GCN 
9438) with the Nordic Optical Telescope equipped with ALFOSC.  We 
obtained 3x600 s R-band frames staring on June 01, 22:04:19 UT, 66.7669 
hr after the burst.

The optical afterglow (Cannizzo et al., GCN 9438) is still detected in 
the stacked frame. The magnitude is R=22.6+/-0.2 against the same 
reference star in Malesani et al. (GCN 9452).

Balman et al. (GCN 9487) found a 3sigma upper limit of R=21.1+/-0.5 mag 
at 15.2 hr after the burst. Our first observation shows R=21.6 mag at 
17.8 hr after the burst. Rossi et al. (GCN 9458) found R=22.2+/-0.2 mag 
at 21.3 hr after the burst, and a break in the light curve at around 22 
ksec post-burst with slopes of 0.5+-0.1 (pre-break) and 1.8+-0.4 
(post-break), using previous obs (Flewelling et al., GCN 9439; Schady et 
al., GCN 9450; Nissinen & Hentunen, GCN 9442). Our new observation 
indicates that the optical decay is becoming much slower. The slower 
optical decay may be due to the presence of a fairly bright host galaxy.

Further optical observations are encouraged.
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