GCN Circular 25959

P. Schady (Univ. of Bath), J. Balmer (MPE Garching), and A. Nicuesa Guelbenzu (TLS Tautenburg) report:


We observed the field of GRB 191004A (Swift trigger 927825; Cenko et al., GCN #25945) 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 01:56 UT on 5th October, 7.8 hours after the GRB trigger. They were performed at an average seeing of 1.4" and at an average airmass of 1.5.


We do not detect a source at the position of the Swift-XRT and MASTER afterglow (Osborne et al., GCN #25950; Lipunov et al., GCN #25944) down to the following 3-sigma limits (all AB magnitude):


g' > 23.7 mag
r' > 24.2 mag
i' > 23.5 mag
z' > 23.3 mag
J > 21.4 mag
H > 20.4 mag
K > 19.9 mag


The given limits are derived based on calibrating the images against Sky-Mapper 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 acknowledge the excellent support from Regis Lachaume in La Silla in acquiring these observations.