GCN Circular 9766
Subject
Title: GRB 090809: Further NOT optical observations
Date
2009-08-11T17:31:56Z (15 years ago)
From
Dong Xu at DARK,NBI <dong@astro.ku.dk>
D. Xu, G. Leloudas, J. P. U. Fynbo, D. Malesani (DARK/NBI), P. Jakobsson
(Univ. Iceland), and and G. Furesz (CfA/Harvard) report on behalf of a
larger collaboration:
We continued to observe the field of GRB 090809 (Markwardt et al., GCN
9754; Xu et al., GCN 9755; Landsman et al., GCN 9758) with the Nordic
Optical Telescope equipped with ALFOSC. We obtained 4x300 s i-band
frames staring on August 10th, 22:25:35 UT, 28.9 hr after the burst.
The optical afterglow is still detected in the stacked frame. The
magnitude is i=22.3+/-0.1 against several reference stars of the USNO B1
catalog in the field. The improved magnitude in our previous observation
is i=20.20+/-0.04, being consistent with the measurement in Wiersema et
al. (GCN 9762). Therefore, the optical afterglow is decaying with a
power-law slope of \alpha=1.0, similar to the general decaying of the
X-ray afterglow (Mao et al., GCN 9759).
We note that the rest-frame T90 (Barthelmy et al., GCN 9756) is less
than 2 s for this burst at z=2.737 (Malesani et al., GCN9761). But the
early energetic X-ray flares tend to make this burst more consistent
with the class of the conventional long bursts.