GCN Circular 13891
Subject
GRB 121024A: GROND Detection of the Optical/NIR Afterglow
Date
2012-10-24T11:31:10Z (12 years ago)
From
Patricia Schady at MPE/Swift <pschady@mpe.mpg.de>
F. Knust, P. Schady and J. Greiner (all MPE Garching) report on behalf
of the GROND team
We observed the field of GRB 121024A (Pagani et al., GCN 13886)
simultaneously in g'r'i'z' with GROND (Greiner et al. 2008, PASP, 120,
405) mounted on the 2.2 m MPG/ESO telescope at La Silla Observatory
(Chile).
Due to clouds, observations only started at 05:53 UT no 24th October,
3 hours after the GRB trigger, and continued until the end of the
night, 3.8 hours later. They were performed at an average seeing of
1.4" and at an average airmass of 1.1.
We find a single point source within the 0.8 arcsec Swift/UVOT error
circle reported by Pagani et al. (GCN 13886) at
RA (J2000.0) = 04:41:53.30
Dec (J2000.0) = -12:17:26.5
with an uncertainty of 0.4" in each coordinate.
Based on the first 142 sec integration in g'r'i'z' and 240 sec
integration in JHK taken at a mid-time of 05:58 UT and 05:54 UT in the
optical and NIR respectively, we estimate preliminary magnitudes (all
in AB system) of
g' = 21.0 +/- 0.2 mag
r' = 20.1 +/- 0.2 mag
i' = 19.8 +/- 0.2 mag
z' = 19.5 +/- 0.2 mag
J = 18.7 +/- 0.1 mag
H = 18.4 +/- 0.1 mag
K = 17.9 +/- 0.1 mag
Given magnitudes are calibrated against GROND zeropoints in the
optical, and 2MASS field stars in the NIR, and are not corrected for
the expected Galactic foreground extinction corresponding to a
reddening of E(B-V) = 0.1 mag in the direction of the burst (Schlegel
et al. 1998).