[vsnet-grb-info 17236] GRB 151111A: GROND confirmation of the afterglow and photometric redshift estimate

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  18598
SUBJECT: GRB 151111A: GROND confirmation of the afterglow and photometric redshift estimate
DATE:    15/11/13 18:01:27 GMT
FROM:    Jan Bolmer at MPE/Garching  <jan at bolmer.de>

J. Bolmer, J. Graham, F. Knust and J. Greiner (all MPE Garching) report:

We reobserved the field of GRB 151111A (Swift trigger 663074; Page et al., GCN 18578) simultaneously in g’r’i’z’JHK
with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2m MPG telescope at ESO La Silla Observatory (Chile).

Observations started at 05:31:33 UT on November 13, about 1.9 days after the GRB trigger.
The initially reported source at the coordinates of RA, Dec = 56.84483, -44.16201 (+/- 0.2“) (Graham et al. GCN 18585)
has clearly faded (e.g. in the r’ band from 22.19 +/- 0.04 to 22.68 +/- 0.05 mag) and we thus conclude that this source is the optical afterglow of GRB 151111A.

Furthermore, after correcting for the galactic foregorund E(B-V)=0.01 mag, and
fitting a powerlaw model to the 7-cannel GROND SED from the first night,
we derive a photometric redshift of z = 3.5 +/- 0.3, according to the g'-band dropout
with g'-r’ =  1.3 mag.