[vsnet-grb-info 15650] GRB 141022A: GROND Detection of a possible Optical Afterglow Candidate

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  16939
SUBJECT: GRB 141022A: GROND Detection of a possible Optical Afterglow Candidate
DATE:    14/10/22 06:18:29 GMT
FROM:    Jochen Greiner at MPI  <jcg at mpe.mpg.de>

D.A. Kann (TLS Tautenburg), T. Schweyer, J. F. Graham, J. Greiner 
(all MPE Garching) report on behalf of the GROND team:

We observed the field of GRB 141022A (Swift trigger 616061; Vargas et
al., GCN #16938) 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 01:39 UT on October 22nd, approximately 20 min
after the GRB trigger. They were performed on a setting target at high
airmass (~2.7) until reaching the pointing limit.

Despite a crowed field we find only a single object in the 2.2"
Swift-XRT enhanced error circle reported by Vargas et al., GCN #16938) at

RA (J2000.0) = 16h 07m 28.82s
DEC (J2000.0) = -72d 07' 29.6"  

(error of 0".5) but cannot ascertain variability in images centered 
875 sec  and 2095 sec after the trigger, and note the possibility 
of a chance coincidence given the density of objects in the field.  
We intended subsequent observations to determine variability.

Based on a 16.5 min sequence of exposures, we estimate preliminary
magnitudes and limits (all in AB system) of:

g' = 23.6 +/- 0.2 mag
r' = 22.2 +/- 0.1 mag
i' = 21.6 +/- 0.1 mag
z' = 22.0 +/- 0.2 mag
J > 20.9 mag
H > 20.3 mag
K > 19.8 mag

Given magnitudes are calibrated against GROND zeropoints and 2MASS field
stars and are not corrected for the expected Galactic foreground
extinction corresponding to a reddening of E_(B-V)=0.1 mag in the
direction of the burst (Schlegel et al. 1998).