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.