[vsnet-grb-info 12103] GRB 120716A: GROND confirmation of the optical/NIR afterglow

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  13492
SUBJECT: GRB 120716A: GROND confirmation of the optical/NIR afterglow
DATE:    12/07/19 06:26:31 GMT
FROM:    Patricia Schady at MPE/Swift  <pschady at mpe.mpg.de>

P. Schady (MPE Garching), M. Nardini (Universita degli studi di
Milano-Bicocca ) and J. Greiner (MPE Garching) report on behalf of the
GROND team:

We observed the field of GRB 120716A (Hurley et al., GCN #13487) at the
position of the afterglow candidate (Cenko et al., GCN #13489)
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 05:07 UT on 2012-07-19, 2.5 days after the GRB
trigger. They were performed at an average seeing of 1.4" and at an
average airmass of 1.3.

We found a single point source at a position consistent the afterglow
candidate reported in Cenko et al. (GCN #13489) and Xu et al. (GCN
#13490). Based on the first 460s of total exposures in g'r'i'z' and 480 s
in JHK, we estimate preliminary magnitudes (all in AB system) of

g' = 21.8 +- 0.1 mag,

r' = 20.9 +- 0.1 mag,

i' = 20.5 +- 0.1 mag,

z' = 20.3 +- 0.1 mag,

J = 19.9 +- 0.2 mag,

H = 19.6 +- 0.2 mag and

K = 18.8 +- 0.5 mag

The optical/NIR SED is well fit by a power-law with a spectral slope of
~1.3, typical for GRB afterglows, confirming this to be the afterglow of
GRB120716A.

Given magnitudes are calibrated against SDSS zeropoints as well as 2MASS
field stars and are not corrected for the expected Galactic foreground
extinction corresponding to a reddening of E_(B-V)=0.07 mag in the
direction of the burst (Schlegel et al. 1998).