GCN Circular 14325

S. Schmidl (TLS Tautenburg), J. Elliott (MPE Garching), A. Nicuesa
Guelbenzu (TLS Tautenburg), S. Klose (TLS Tautenburg), and J. Greiner
(MPE Garching) report on behalf of the GROND team:

We observed the field of GRB 130315A (Swift trigger 551126; Evans et
al., GCN 14311
Not found
 
 
) simultaneously in g'r'i'z'JHK with GROND (Greiner et al.
2008, PASP 120, 405) mounted at the 2.2 m MPG/ESO telescope at La Silla
Observatory (Chile).

First-epoch observations started on March 15, 2013, at 23:51 UT, 11.1
hrs after the GRB trigger. They were performed at an average seeing of
0."7 and at an average airmass of 1.18. No evidence for a fading
afterglow was found.

Second-epoch observations were executed the following night (38.4 hr
after the trigger) under slightly worse observing conditions. A
comparison with the first-epoch images reveales a fading source at the
south-east border of the Swift/XRT error circle (Page et al., GCN 14317
Not found
 
 
)
at coordinates

RA (J2000.0)  =  10:30:11.54
Dec (J2000.0) = -51:47:39.8

with an uncertainty of 0."5 in each coordinate.

Based on a total exposure time of 1500 s in r'i'z' at a midtime of
12.8 hrs after the burst, for this source we measure the following
preliminary AB magnitudes:

r' = 22.0 +/- 0.1,
i' = 21.5 +/- 0.1,
z' = 21.1 +/- 0.1.

Between both epochs this object faded by more than 1 magnitude, implying
a decay with alpha > 0.75.

The given magnitudes are calibrated against GROND zeropoints. The
Galactic reddening along the line of sight is E(B-V)= 0.36 mag (Schlegel
et al. 1998).