GCN Circular 23371

P. Schady (Univ. of Bath) and J. Bolmer (MPE, Garching) report:


We observed the field of GRB 181022A (Swift trigger 868312; Marshall et al., GCN #23364) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2 m MPG telescope at ESO La Silla Observatory (Chile).


Observations started at 01:53 UT on 2018-10-23, 8.4 hrs after the GRB trigger. They were performed at an average seeing of 1.4" and average airmass of 1.8.


Based on a total of 16 mins integration time, we do not detect a source within the Swift-XRT error circle reported by Marshall et al. (GCN #868312) down to the following 3 sigma AB magnitudes:


g' > 22.8 mag

r' > 22.9 mag

i' > 22.7 mag

z' > 22.5 mag

J > 21.3 mag

H > 20.8 mag

K > 18.9 mag


The given limits are derived based on calibrating the images against GROND zeropoints and 2MASS field stars and are not corrected for the Galactic foreground extinction corresponding to a reddening of E_(B-V)= 0.01 in the direction of the burst (Schlafly & Finkbeiner 2011).


We thank Markus Rabus for the excellend support from La Silla.