TITLE:   GCN CIRCULAR
NUMBER:  14364
SUBJECT: GRB 130408A: GROND detection of the afterglow
DATE:    13/04/09 00:38:53 GMT
FROM:    Alexander Kann at TLS Tautenburg  <kann@tls-tautenburg.de>

V. Sudilovsky (MPE Garching), A. Nicuesa Guelbenzu (TLS Tautenburg) and
J.Greiner (MPE Garching) report on behalf of the GROND team:

We observed the field of GRB 130408A (Swift trigger 553132; Lien et al.,
GCN 14361) simultaneously in g'r'i'z'JHK 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 23:22 UT on April 8th, 1.5 hrs after the GRB
trigger. They were performed at an average seeing of 1.0 and at an average
airmass of 1.0.

Based integrations of 260s in the optical and 240s in the NIR taken at a
mid-time of UT 23:34, we detect the variable source reported by Melandri
et al. (GCN 14362) and Siegel & Lien (GCN 14363), with preliminary
magnitudes (all AB):

g' = 21.0 +- 0.1,
r' = 19.7 +- 0.1,
i' = 19.1 +- 0.1,
z' = 18.8 +- 0.1,
J = 18.0 +- 0.1,
H = 17.8 +- 0.1, and
K > 17.0.

The large r-g color implies a redshift of z>3. Observations are ongoing.

Given magnitudes are calibrated against GROND zeropoints in g'r'i'z' and
2MASS field stars in JHK. They are not corrected for the Galactic
foreground extinction corresponding to a reddening of E_(B-V)= 0.26 mag in
the direction of the burst (Schlegel et al. 1998).