GCN Circular 13881

D. A. Kann (MPE/Universe Cluster), M. Nardini (Milano-Bicocca), and J.
Greiner (MPE) report on behalf of the GROND team:

We observed the field of GRB 121017A (Swift trigger 536172, Grupe et al.,
GCN # 13875) 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 on October 17, 2012, at 23:50 UT, 4.45 hr after the
GRB trigger. They were performed at an average seeing of 1" (in r') and at
an average airmass of 1.3.

We do not detect any sources in the enhanced XRT error circle (Goad et
al., GCN # 13879), in agreement with earlier reports of optical
observations (Jelínek et al., GCN # 13876, Volnova et al., GCN # 13877,
Gorosabel & Mottola, GCN # 13878). There is a star at the eastern edge of
the error circle but this affects only a small part of it.

Based on 284 s of total exposures in g'r'i'z' (mean time 0.18978 days
after the trigger) and 480 s in JHK (mean time 0.19003 days after the
trigger) we estimate preliminary AB magnitudes (upper limits are 3 sigma)
of

g' > 23.2,

r' > 23.2,

i' > 22.4,

z' > 22.2,

J  > 19.8,

H  > 19.4 and

K  > 19.3.

Given magnitudes are calibrated against GROND zeropoints in the optical as
well as 2MASS field stars in the NIR and are not corrected for the high
Galactic foreground reddening of E_(B-V) = 0.44 mag (Schlegel et al.
1998).