[vsnet-grb-info 20408] GROND observations of GRB 180316A

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22504
SUBJECT: GROND observations of GRB 180316A
DATE:    18/03/16 10:40:27 GMT
FROM:    Patricia Schady at MPE/Swift  <pschady at mpe.mpg.de>

P. Schady and S. Steinmassl (both MPE) report:

We observed the field of GRB 180316A (Swift trigger 814677; Melandri et
al., GCN #22500) simultaneously in g'r'i'z'JHK with GROND (Greiner et al.
2008, PASP 120, 405) mounted at the 2.2 m MPG telescope at ESO La Silla
Observatory (Chile).

Observations started at 06:46 UT on March 16, 1.8 hours after the GRB
trigger. They were performed at an average seeing of 1.5" and at an
average airmass of 1.5.

We clearly detect the NIR/optical transient of GRB 180316A within the
enhanced XRT position (Evans et al., GCN #22501), in agreement with the
optical transient detected with MASTER (Lipunov et al., GCN #22502,
#22503). Based on the first 4 minutes of exposure, we measure the
following magnitudes (all in AB system):

g' = 19.4 +/- 0.1 mag
r' = 19.0 +/- 0.1 mag
i' = 18.9 +/- 0.1 mag
z' = 18.8 +/- 0.1 mag
J = 18.2 +/- 0.1 mag
H = 18.0 +/- 0.1 mag
K = 17.8 +/- 0.2 mag

Given magnitudes are calibrated against GROND zeropoints in g'r'i'z' and
2MASS field stars in JHK, and are not corrected for the Galactic
foreground extinction corresponding to a reddening of E_(B-V)= 0.24 in the
direction of the burst (Schlafly & Finkbeiner 2011).

We acknowledge the excellent support from the TiO and the current observer
at the 2.2m in La Silla, Sam Kim and Charlotte Brand.