GCN Circular 19349
Subject
GRB 160425A: GROND observation
Event
Date
2016-04-26T09:20:09Z (10 years ago)
From
Jochen Greiner at MPI <jcg@mpe.mpg.de>
J. Bodensteiner (MPE Garching), S. Schmidl (TLS Tautenburg), and
J. Greiner (MPE Garching) report on behalf of the GROND team:
We observed the field of GRB 160425A (Swift trigger 684098; Krimm et al.
GCN Circ. 19343) 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 04:38 UT on April 26, 2016, 5.2 hrs after the GRB
trigger. They were performed at an average seeing of 3.1" and at an
average airmass of 1.2.
We detect an optical source at the position reported by Krimm et al.
(GCN 19343) and Lipunov et al. (GCN 19344).
Based on total exposures of 24 minutes in g'r'i'z' and 20 minutes in
JHK, at a midtime of 7.16 hrs after the burst, we measure the following
preliminary magnitudes and upper limits (AB magnitude system):
g' = 22.2 +/- 0.3 mag,
r' = 21.1 +/- 0.2 mag,
i' = 20.7 +/- 0.2 mag,
z' = 20.5 +/- 0.1 mag,
J = 19.7 +/- 0.2 mag,
H = 19.4 +/- 0.3 mag, and
K > 18.3 mag.
The magnitudes and upper limits are calibrated against GROND zeropoints
and 2MASS field stars and are not corrected for the Galactic foreground
extinction corresponding to a reddening of E_(B-V)= 0.06 mag in the
direction of the burst (Schlegel et al. 1998).
Relative to the UVOT and MASTER reports, the source has faded, though
we do not detect significant fading in our data so far (strongly mitigated
by the bad conditions). We therefore cannot distinguish between afterglow
or host flux.