V. Sudilovsky, K. Varela, D. A. Kann and J. Greiner
(all MPE Garching) report on behalf of the GROND team:
We observed the field of the GRB 131024A (Racusin et al., GCN #15365)
simultaneously in g'r'i'z'JHKs with GROND (Greiner et
al. 2008, PASP 120, 405) mounted at the 2.2 m MPG telescope at La Silla
Observations started at 00:20 UT on 25 October 2013, 12 hours after the
GRB. They were performed at an average seeing of 1.6" and at an average
airmass of 1.4.
Based on two co-added observations with individual exposure times of 1500s
in g'r'i'z' and 1200s in JHK, we do not detect any source with the
enhanced XRT circle (Osborne et al., GCN #15367) down to preliminary
limiting magnitudes (all in the AB system):
g' > 25.1 mag,
r' > 24.7 mag,
i' > 23.9 mag,
z' > 23.8 mag,
J > 21.6 mag,
H > 21.0 mag,
K > 20.0 mag.
We do note there is a marginally detected source in r' at roughly 1.6"
north-east of the center of the error circle.
Magnitudes are calibrated against GROND zeropoints (griz) and 2MASS stars
are not corrected for the Galactic foreground extinction corresponding to
a reddening of E_(B-V)=0.04 mag in the direction of the burst (Schlegel
et al. 1998).