[vsnet-grb-info 17902] GRB 160425A: GROND observation

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  19349
SUBJECT: GRB 160425A: GROND observation
DATE:    16/04/26 09:20:09 GMT
FROM:    Jochen Greiner at MPI  <jcg at 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.