GCN Circular 20457
T. Kruehler (MPE Garching) reports: I observed the field of GRB 170113A (Swift trigger 732526; Evans et al. GCN #20446) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2m MPG telescope at the ESO La Silla Observatory (Chile). Observations started at 01:34 UT on 2017-01-14, 15.5 hr after the GRB trigger. Based on combined images with 22 min of total exposure time in g'r'i'z' and 18 min in JHK at a mid-time of 01:50 UT on 2017-01-14, I derive the following preliminary magnitudes and upper limits (all in the AB system) for the optical/NIR afterglow (Evans et al., GCN 20446, Guidorzi et al., GCN 20448, Siegel et al., GCN 20455): g' = 22.3 +- 0.1 mag r' = 22.0 +- 0.1 mag i' = 21.8 +- 0.1 mag z' = 21.6 +- 0.1 mag J = 20.9 +- 0.2 mag H = 20.8 +- 0.3 mag K > 19.0 mag Given magnitudes are calibrated against GROND zeropoints and 2MASS field stars and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V)=0.099 mag in the direction of the burst (Schlafly & Finkbeiner 2011). I acknowledge excellent help in obtaining these data from the supporting astronomer on La Silla, Regis Lachaume.