GCN Circular 9720
Subject
GRB 090715B: Late-time Lick 3m observations
Event
Date
2009-07-28T06:13:01Z (16 years ago)
From
Daniel Perley at U.C. Berkeley <dperley@astro.berkeley.edu>
D. A. Perley, N. R. Butler, and S. B. Cenko (UC Berkeley) report:
We obtained additional, late-time imaging of the field of GRB 090715B
(GCN 9668, Vetere et al.; GCN 9670, Smith et al.) with the Lick 3m
telescope (+PFCam) in the R-band filter under dark skies, good seeing
conditions and thin cloud cover. Observations were conducted on the
night of 2009-07-24 (UT) between 04:46 and 06:15 UT, and consisted of
seven 300-second exposures followed by four 600-second exposures.
The afterglow is faintly detected in the combined image. Photometry
relative to the reference star of Malesani et al. (GCN 9671) gives a
magnitude of R = 23.6 +/- 0.3 mag at this time (t = 8.35 days after the
GRB).
Relative to the NOT observation at 2.06 days (Malesani et al., GCN
9687), this corresponds to a decay index of alpha ~ 1.5, indicating that
the unusually long period of slow fading has ended and the optical
afterglow has resumed a "normal" power-law decay.