{
  "bibcode": "2012GCN.13003....1E",
  "body": "J. Elliott, J. Greiner, F. Olivares E., A. Rau (all MPE Garching),\nT. Kruehler (DARK) report on behalf of the GROND team:\n\nWe observed the field of GRB 120302A (Sakamoto et al., GCN #13000)\nsimultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP,\n120, 405) mounted at the 2.2 m ESO/MPI telescope at La Silla\nObservatory (Chile). Observations centered on the BAT position started\non March 3, 2012, at 00:33 UT, 22.6 h after the GRB trigger. They were\nperformed at an average seeing of 1.4\", and average airmass of 2.\n\nA second epoch of GROND observations was taken starting March 4, 2012, at\n01:47 UT, only 15 deg from the Moon. The pointing had been slightly shifted \nto the south-west to cover the X-ray source in the Swift ToO observation\nalso in the optical channels. Our images reveal no source within the formal\n4.7\" XRT error circle centered at RA (2000.0) = 08 09 35.96, \nDecl. (2000.0) = 29 37 43.8. \n\nSlightly outside the XRT error circle, we find a source at\nRA (2000.0) = 08 09 35.58\nDecl. (2000.0) = 29 37 40.7\n(+-0.2 arcsec). This source has been constant between our two epochs in JHK. \nIn the second epoch, we measure for this object (all in the AB system)\n\ng' = 22.5 +/- 0.3\nr' = 21.9 +/- 0.2\ni' = 21.9 +/- 0.3\nz' = 21.4 +/- 0.1\nJ  = 20.9 +/- 0.4\nH  = 20.3 +/- 0.3\nK  = 19.7 +/- 0.4\n\nwhere the optical bands have been calibrated against SDSS, and the NIR bands\nagainst 2MASS. This object is not visible on SDSS images, suggesting a\ntransient nature. The above magnitudes, after correcting for the small reddening \nof E(B-V)=0.04 mag (Schlegel et al. 1998), are well fitted with a power law \nof slope 1.4, typical for GRB afterglows. We therefore propose this \nsource as the candidate afterglow of GRB 120302A. The constant flux during\nour two epochs might be the result of a plateau or re-brightening event.\n\nNote, that there is a nearby SDSS source, SDSS J080935.14+293739.8, which based \non our astrometry is definitely a different source, though it is not \ndetected in our images due to the high background of the nearby Moon. \nA finding chart will be placed at http://www.mpe.mpg.de/~jcg/grb120302A.html.\nWe note that the colors of SDSS J080935.14+293739.8 are not consistent with\nan AGN or star. If SDSS J080935.14+293739.8 is a galaxy, the large r'-i'\ncolor might indicate a redshift of about 0.7-0.8. This could potentially \nbe the host galaxy of GRB 120302A.\n\nA deep observation is suggested in a few days time, when the Moon does not \ndisturb so much anymore.",
  "circularId": 13003,
  "createdOn": 1330971992000,
  "email": "jcg@mpe.mpg.de",
  "subject": "GRB 120302A: GROND detection of an afterglow candidate",
  "submitter": "Jochen Greiner at MPI  <jcg@mpe.mpg.de>",
  "eventId": "GRB 120302A"
}