{
  "bibcode": "2009GCN.10158....1A",
  "body": "P. Afonso, T. Kruehler, A. Rau, and J. Greiner (all MPE Garching) report \non behalf of the GROND team:\n\n\nGROND (Greiner et al. 2008, PASP 120, 405), mounted at the 2.2m ESO/MPI \ntelescope at La Silla Observatory (Chile), observed the field of GRB \n091109A (Oates et al., GCN #10138) simultaneously in the g'r'i'z'JHK bands.\n\nObservations were done under clear sky conditions, starting on Nov 10 at \n00:07 UTC, 19.1 h after the burst and lasted for 1.8 hours.\n\nIn stacked images corresponding to a total integration time of 60 min in \nJHK and 75 min in g'r'i'z', we detect the optical afterglow (Oates et \nal., GCN #10138, Guidorzi et. al, GCN #10142) in the g'r'i'z' bands and \nobtain the following preliminary magnitudes and upper limits (all in the \nAB system):\n\ng' = 24.5 +/- 0.1\nr' = 23.6 +/- 0.1\ni' = 23.4 +/- 0.1\nz' = 23.3 +/- 0.2\nJ > 22.2\nH > 21.8\nK > 21.2\n\nwhich were derived using the GROND zero points and 2MASS catalog field \nstars as reference. No correction has been made for the expected \nextinction corresponding to a reddening of E(B-V) = 0.03 mag in the \ndirection of the burst (Schlegel et al. 1998).\n\nAssociating the blue g'-r' color with Lyman-alpha absorption in the host \nof the GRB, we obtain a photometric redshift of z = 3.5 +/- 0.4 assuming \nno intrinsic dust.\n\nIn addition, we triggered VLT/FORS2 spectroscopy, that started Nov 10 at \n02:23 UTC, 21.5 h post-burst. Two integrations of 1800 s each at a mean \nairmass of 2.1 were obtained using the 600RI grism that covers the \nwavelength range from 5300 to 8700 A.  In the low S/N spectrum we find a \ntentative ~60A EW broad absorption feature around a wavelength of 5700A. \nIf associated with Lyman-alpha absorption, the corresponding redshift of \n~3.5 would be in agreement with the GROND photo-z.\n\nWe note, however, that all observations are also consistent with a host \ngalaxy at a redshift of z ~ 0.44. Given the absence of information about \na possible host galaxy contribution we cannot distinguish these two \npossibilities at this point.\n\nWe thank A. Smette and P. Lynam at Paranal for excellent support.",
  "circularId": 10158,
  "createdOn": 1257865153000,
  "email": "kruehler@mpe.mpg.de",
  "subject": "GRB 091109A: GROND and VLT observations",
  "submitter": "Thomas Kruehler at MPE/MPI  <kruehler@mpe.mpg.de>",
  "eventId": "GRB 091109A"
}