GCN Circular 13409

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

We observed the field of GRB 120701A (Swift trigger 525477; Barthelmy et 
al., GCN #13404) 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).

Observations started at 09:11 UT on 2012-07-01, 1.34 hr after the GRB 
trigger. They were performed at an average seeing of 1.6 arcsec and at an 
average airmass of 2.5. A second epoch observation was performed 25.3 hr 
after the the trigger.

Inside the 1.8 arcsec XRT error circle (Evans et al., GCN #13406) we 
detect a fading object in all bands at coordinates RA(J2000) = 
05:21:23.52, DEC(J2000) = -58:32:58.3 (+/- 0.3 arcsec).

During the first night we obtained exposures of 3120s in JHK and 2550s in 
g'r'i'z'. At a mid time of 2.08 hrs after the trigger we measure the 
following preliminary magnitudes (all in the AB system)

  g' = 21.7 +- 0.1,
  r' = 21.3 +- 0.1,
  i' = 20.8 +- 0.1,
  z' = 20.8 +- 0.1,
  J  = 20.3 +- 0.1,
  H  = 20.5 +- 0.2,
  K  = 20.1 +- 0.3.

The object faded in r' by about 1.0 mag between the first and the second 
epoch. We therefore propose this source to be the afterglow of GRB 
120701A.

All magnitudes are derived based on calibrating the images against GROND 
zeropoints and 2MASS field stars. The Galactic reddening along the line of 
sight is E(B-V) =0.02 mag (Schlegel et al. 1998).