TITLE:   GCN CIRCULAR
NUMBER:  14639
SUBJECT: GRB 130513A: GROND observations
DATE:    13/05/14 16:20:57 GMT
FROM:    Alexander Kann at TLS Tautenburg  <kann@tls-tautenburg.de>

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

We observed the field GRB 130513A (INTEGRAL trigger 6842; Mereghetti et
al., GCN 14630) simultaneously in g'r'i'z'JHKs with GROND (Greiner et al.
2008, PASP 120, 405) mounted at the 2.2 m MPG/ESO telescope at La Silla
Observatory (Chile).

Observations started in twilight at 22:54:57 UT on May 13th, 15.3 hours
after the IBAS trigger. They were performed at an average seeing of 1".0
and at an average airmass of 1.1.

Inside the 2".7 refined XRT error circle (Evans et al., GCN 14635), we do
not detect any sources. Based on an observation with 1500 s integration
time in g'r'i'z' and 1200 s integration time in JHK, centered at 0.6959
days after the trigger, we estimate preliminary 3-sigma upper limits (all
in AB system) of

g' > 25.4,
r' > 24.9,
i' > 24.2,
z' > 23.9,
J  > 21.4,
H  > 20.6 and
K  > 20.2.

We note that if the XRT source is indeed the afterglow, then it is very
faint optically. Galactic extinction is negligible.

Given magnitudes are calibrated against GROND zero points (g'r'i'z') as
well as 2MASS field stars (JHK) and are not corrected for the expected
Galactic foreground extinction corresponding to a reddening of
E_(B-V)=0.03 mag in the direction of the burst (Schlegel et al. 1998).