GCN Circular 15585

S. Schmidl (TLS Tautenburg ), K. Varela and J. Greiner (both MPE Garching)
report on behalf of the GROND team:

We observed the field of the GRB 131205A (Ukwatta et al., GCN #15578
Not found
 
 
)
simultaneously in g'r'i'z'JHKs 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 05:07 UT on 06 December 2013, 19.5 hours after the
GRB. They were performed at an average seeing of 1.0" and at an average
airmass of 1.3.

Based on six co-added observations with individual exposure times of 1500s
in g'r'i'z' and 1200s in JHK, we do not detect any source inside the
enhanced XRT error circle (Beardmore et al., GCN #15580
Not found
 
 
) down to
preliminary 3 sigma limiting magnitudes (all in the AB system) :

g' > 25.8 mag,
r' > 25.6 mag,
i' > 24.9 mag,
z' > 24.5 mag,
J > 22.1 mag,
H > 21.5 mag,
K > 20.8 mag.

Magnitudes are calibrated against GROND zeropoints (griz) and 2MASS stars
(JHK), and are not corrected for the Galactic foreground extinction
corresponding to a reddening of E_(B-V)=0.25 mag in the direction of the
burst (Schlegel et al. 1998).

We note the marginal detection of a source, located 1.9" from the center
of the XRT circle, at

RA : 08:46:30.86
DEC : -60:09:20.6,

with an uncertainty of 0.2 arcsec and magnitudes of

r = 24.8 +/- 0.2
i = 24.7 +/- 0.3
z = 24.3 +/- 0.3.

This is consistent with a power law and thus could be the afterglow of
GRB131205A, but no statement can be made about fading at this time.
Follow-up observations are required to determine the nature of this
source.