GCN Circular 26176

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


We observed the field of GRB 161019A (Swift trigger 929744; Gropp et al., GCN #26008) 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 04:19 UT on 2019-10-16, 10 min after the GRB trigger. They were performed at an average seeing of 1.7" and at an average airmass of 1.7.


We detect a bright point source in all optical and near-infrared filters consistent with the reported optical afterglow position (Watson et al., GCN #26010; Siegel et al., GCN #26024). Based on the first 3.3 min of total exposures in g'r'i'z'JHK, we estimate preliminary AB magnitudes of


g' = 16.81 +/- 0.03
r' = 16.33 +/- 0.03
i' = 15.84 +/- 0.04
z' = 15.51 +/- 0.04
J = 15.28 +/- 0.05
H = 14.80 +/- 0.05
K = 14.83 +/- 0.08


Given magnitudes are calibrated against SDSS and 2MASS field stars and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V)=0.09 in the direction of the burst (Schlafly & Finkbeiner 2011).

We acknowledge the excellent support provided by the telescope operator at La Silla.