GCN Circular 11774
Subject
GRB 110305A: GROND Detection of Optical Afterglow
Event
Date
2011-03-05T11:56:58Z (15 years ago)
From
Patricia Schady at MPE/Swift <pschady@mpe.mpg.de>
A. Nicuesa Guelbenzu (TLS Tautenburg), V. Sudilovsky, P. Schady and J.
Greiner (MPE Garching) report on behalf of the GROND team:
We observed the field of GRB 110305A (Swift trigger 448229; Grupe et
al., GCN #11773) simultaneously in g'r'i'z'JHK with GROND (Greiner et
al. 2008, PASP 120, 405) mounted at the 2.2m MPI/ESO telescope at La
Silla Observatory (Chile).
Observations started at 06:40 UT on March 5th, 2 minutes after the GRB
trigger. They were performed at an average seeing of 0.8" and at an
average airmass of 1.8.
We found a fading source within the 2.2" Swift/XRT error circle
reported by Grupe et al. (GCN #11773) at
RA (J2000.0) = 17h 23m 31.3s
DEC (J2000.0) = -15d 48' 08.8"
with an uncertainty of 0.3" in each coordinate.
The source decayed by 0.8mag in 60.5 minutes, suggesting that it is
the optical afterglow of GRB110305A. At T+116.9 minutes the source had
an r'-band magnitude of 23.7 +/- 0.1.
These measurements are not corrected for the considerable Galactic
foreground extinction corresponding to a reddening of E(B-V)=0.390 mag
in the direction of the burst (Schlegel et al. 1998).