TITLE: GCN CIRCULAR NUMBER: 15373 SUBJECT: GRB 131024A: GROND upper limits DATE: 13/10/25 02:06:46 GMT FROM: Vladimir Sudilovsky at MPE 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 Observatory (Chile). 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 (JHK), and 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).