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GCN Circular 9002

GRB 090313: MITSuME Okayama observation
2009-03-16T09:58:21Z (15 years ago)
Michitoshi Yoshida at Okayama Astrophysical Obs <>
M. Yoshida, D. Kuroda, K. Yanagisawa, Y. Shimizu, S. Nagayama,
H. Toda (OAO, NAOJ) and N. Kawai (Tokyo Tech) report on behalf
of the MITSuME collaboration:

We observed the field of GRB 090313 (Mao et al. GCN 8980) with
the optical three-color (g', Rc and Ic) CCD camera attached to
the MITSuME 50cm telescope of Okayama Astrophysical Observatory.
The observation started on 2009-03-14 14:27:51 UT (29.34 hours
after the alert). We detected a point source at the position of
the X-ray - optical - IR afterglow (Chornock and Filippenko GCN
8979; Mao et al. GCN 8991; Updike et al. GCN 8983; Vaalsta et al.
GCN 8996; de Ugarte Postigo et al. GCN 8992, GCN 8999; Perley
GCN 8997; Perley et al. GCN 9001) in Ic band. Photometric result
is listed below. We used GSC2.3 catalog for flux calibration.

Mid-UT                Td           Exp.Time      Ic
2009-03-14 16:30:24   31.3775 hr   60sec x 171   19.3 +/- 0.2

Our result and previous reports (Vaalsta et al. GCN 8996; Perley
GCN 8997; de Ugarte Postigo et al. GCN 8999) show that the
afterglow maintained its brightness from 10 hours to 30 hours
after the burst. de Ugarte Postigo et al. (GCN 8999) and Perley
et al. (GCN 9001) reported steep decline of the I band magnitude
of the object after our observation. Thus the break point of the
light curve may exist at around 31 hours after the burst.
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