GCN Circular 13048
Subject
GROND observations of GRB 120311A
Event
Date
2012-03-12T15:19:16Z (15 years ago)
From
Vladimir Sudilovsky at MPE <vsudilov@mpe.mpg.de>
V. Sudilovsky, T. Prinz, and J. Greiner (all MPE Garching) report on behalf of the GROND team:
We observed the field of GRB 120311A (Markwardt et al., GCN #13032)
simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP, 120, 405)
mounted at the 2.2 m MPI/ESO telescope at La Silla Observatory (Chile).
Observations centered on the BAT position started on March 11, 2012, at
08:02 UT, 2.5h after the GRB trigger. They were performed at an average
seeing of 1.0", and average airmass of 1.8.
Based on a 20 minute exposure centered at 09:09 UT, the afterglow candidate
reported by Melandri et al. (GCN 13033) is measured as follows (all in the AB
system and calibrated against GROND zeropoints (g'r'i'z') and 2MASS (JHK)):
g' = 22.9 +/- 0.3
r' = 22.5 +/- 0.1
i' = 22.4 +/- 0.1
z' = 22.0 +/- 0.1
J > 20.5
H > 19.6
K > 18.0
These above magnitudes have not been corrected for the Galactic extinction of
E(B-V) = 0.13 towards the direction of the burst (Schlegel et al. 1998).
These magnitudes imply a fading of more than two magnitudes relative to the
observations reported by Melandri et al. (GCN 13033), and thus confirm
the afterglow nature of this object.