GCN Circular 9687
Subject
GRB 090715B: further NOT optical observations
Date
2009-07-18T15:31:46Z (15 years ago)
From
Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst <malesani@astro.ku.dk>
D. Malesani (DARK/NBI), G. C. Cox (NOT), C. Mackay, D. King, T. Staley
(IoA Cambridge), and P. Jakobsson (Univ. Iceland) report on behalf of a
larger collaboration:
We observed again the field of GRB 090715B (Vetere et al., GCN 9668)
using the NOT telescope equipped with the StanCam instrument. The
optical afterglow (Vetere et al., GCN 9668; Smith et al., GCN 9670) is
well detected in the V and R filters, and is still bright. Using the
same reference star as in GCN 9671, we measure R ~ 21.3 on mean time
July 17.94 UT (2.06 days after the GRB).
Assuming an unbroken power-law fading (Fnu propto t^-alpha), the
corresponding decay index is alpha ~ 0.44, which is unusually flat at
such late epoch (although not unprecedented). Our measurement is also
consistent within the uncertainties with the broken power-law fit
reported by Guidorzi et al. (GCN 9677).
DM thanks Carole G. Mundell and Cristiano Guidorzi for discussion.