[vsnet-grb-info 7765] GRB 090427: GROND observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9319
SUBJECT: GRB 090427: GROND observations
DATE:    09/05/04 00:07:14 GMT
FROM:    Felipe Olivares Estay at MPE  <felipe at mpe.mpg.de>

F. Olivares, T. Kruehler, J. Greiner (all MPE Garching) report on behalf of
the GROND team: 

We observed the central area of the error box of GRB 090427 localized by the
IPN (Pal'shin et al., GCN #9277) simultaneously in g'r'i'z'JHK with GROND
mounted at the 2.2m ESO/MPI telescope at La Silla Observatory (Chile).
Three adjacent pointings centered at 

RA = 15,43,31.0  Decl. = -13,40,00
RA = 15,43,43.4  Decl. = -13,30,00 (center of IPN box)
RA = 15,43,55.0  Decl. = -13,20,00 

have been observed with our 10x10 arcmin (in JHK) and 5.4x5.4 arcmin
(g'r'i'z') field-of-view, thus covering about 27% and 8% of the full error
box respectively (see sketch at http://www.mpe.mpg.de/~jcg/grb090427.html). 

Observations started on 29 Apr. 2009 at 06:20 UT, 30.9 h after the burst,
and consisted, for each of the three fields, of a set of images with a
total integration time of 8 min in JHK and 7.7 min in g'r'i'z'. A second
epoch of all three fields was obtained on 30 Apr. 2009 starting at 05:18 UT. 

Image subtraction of the two epochs does not reveal a variable source
in any of the three fields, down to limiting magnitudes (all in AB system) 
of 

g' > 23.9
r' > 23.8
i' > 23.5
z' > 23.2
J > 22.2
H > 21.7
K > 20.6 

These magnitudes have been obtained using 2MASS field stars and the GROND
zeropoints as reference.