GCN Circular 19150

J. Bolmer, J. Greiner (both MPE Garching) and D.A. Kann (TLS Tautenburg) report on
behalf of the GROND team:

We re-observed the field of GRB 160303A (Swift trigger 677495; Beardmore et
al., GCN #19126) 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 03:58 UT on 2016-03-05, 41.1h after the GRB
trigger. They were performed at an average seeing of 1.0" and at an
average airmass of 1.6.

We still detect a faint source at the initially reported position (Graham et al. GCN#19144,
de Ugarte Postigo et al. (GCN #19136)).

Based on 96 min of exposure in g'r'i'z', at a mid-time
of 04:52 UT, we derive the following preliminary magnitudes and upper
limits (in AB system):

g' = 25.2 +/- 0.2 mag,
r' = 25.1 +/- 0.2 mag,
i' > 24.3 mag,
z' > 24.4 mag,

Given detections and upper limits are calibrated against SDSS field stars. 
No correction for the expected Galactic foreground extinction corresponding
to a reddening of E_(B-V)=0.014 mag in the direction of the burst
(Schlafly & Finkbeiner 2011) has been applied.

Combining our GROND measurements with those from 10.63 h after the GRB
(de Ugarte Postigo et al., GCN #19136), we obtain a decay slope of
alpha = - 1.1 +/- 0.2 in the r' band.