TITLE:   GCN CIRCULAR
NUMBER:  14386
SUBJECT: GRB 130418A: GROND detection of the optical-NIR afterglow 
DATE:    13/04/19 02:58:43 GMT
FROM:    Mohit Tanga at MPE/GROND  <mohit@mpe.mpg.de>

GRB 130418A: GROND detection of the optical-NIR afterglow

M. Nardini (UNIMIB), M. Tanga (MPE Garching), D. A. Kann (TLS Tautenburg)
and J. Greiner (MPE Garching) report on behalf of the GROND team:

We observed the field GRB 130418A (Swift trigger 553847; M. De Pasquale et
al., GCN 14377) simultaneously in g'r'i'z'JHKs with GROND (Greiner et al.
2008, PASP 120, 405) mounted at the 2.2 m MPG/ESO telescope at La Silla
Observatory (Chile).

Observations started at 01:20:33 UT on April 19th, 6.3 hrs after the SWIFT
BAT trigger. They were performed at an average seeing of 1" and at an
average airmass of 1.38.

We detect the optical afterglow inside the 0.7" Swift/UVOT error circle
reported by De Pasquale et al., (GCN 14377) in all 7 bands. Based on the
first 4 min of total exposure we estimate preliminary magnitudes (all in
AB system) of

g' = 18.79 +- 0.03,
r'  = 18.46 +-0.03,
i'  = 18.22 +- 0.03,
z' = 17.95 +- 0.03,
J  = 17.62 +- 0.05,
H = 17.17 +- 0.05 and
K = 16.81 +- 0.11

Given magnitudes are calibrated against SDSS as well as 2MASS field stars
and are not corrected for the expected Galactic foreground extinction
corresponding to a reddening of E_(B-V)=0.03 mag in the direction of the
burst (Schlegel et al. 1998).