GCN Circular 16089

GRB 140408A: GROND Detection of an Afterglow Candidate
  
K. Varela, C. Delvaux (both MPE Garching), D.A. Kann (TLS 
Tautenburg), and J. Greiner (MPE Garching) report on behalf of the
GROND team:
  
We observed the field of GRB 140408A (Swift trigger 595141; d'Elia et 
al., GCN #16082) 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 La
Silla Observatory (Chile).

Observations started at 06:16:31 UT on 8th April 2014, 0.709 days
after the  GRB trigger. They were performed at an average seeing of
0".9 and at an average airmass of 1.6.
  
We find a single point source within the 2".2 Swift-XRT error circle
reported by Evans et al. (GCN #16085) at 
  
RA (J2000.0) = 19h 22m 51.78s  
Dec. (J2000.0) = -12d 35' 40.9" 
  
with an uncertainty of 0".4 in each coordinate.
  
Based on a 7380 s exposure on g'r'i'z' , and a 6000 s exposure in
JHK, we estimate preliminary magnitudes (all in AB system) of
  
g' = 25.6 +- 0.3 mag,
r' = 23.7 +- 0.2 mag,
i' = 22.7 +- 0.2 mag,
z' = 22.8 +- 0.3 mag,
J > 22.0 mag,
H > 21.5 mag, and
K > 20.0 mag.

We propose this source to be a candidate afterglow for GRB 140408A.
At the moment, fading can not be established. If it is the afterglow,
the SED suggests a redshift of z ~ 4.

Given magnitudes are calibrated against GROND zeropoints as well as
2MASS field stars and are not corrected for the expected Galactic  
foreground extinction corresponding to a reddening of E_(B-V)=0.16 
mag in the direction of the burst (Schlafly & Finkbeiner 2011).

[GCN OPS NOTE(10apr14): The missing minus sign on the Declination value
in the 3rd paragraph was added. Acknowledgement to F.Marshall.]