{
  "bibcode": "2009GCN..9773....1U",
  "body": "Adria Updike (Clemson University), Arne Rau, Thomas Kruehler, Felipe \nOlivares, and Jochen Greiner (all MPE Garching) report on behalf of the \nGROND team:\n\nWe observed the field of GRB 090812 (Swift trigger 359711; Stamatikos et \nal., GCN #9768) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. \n2008, PASP 120, 405) mounted at the 2.2 m ESO/MPI telescope at La Silla \nObservatory (Chile).\n\nDue to cloud coverage, observations started only at 08:13 UT on August 12, \n2 hours and 11 minutes after the GRB trigger. They were performed at an \naverage seeing of 1.1\" and at an average airmass of 1.2 with light cirrus, \nand continued until twilight.\n\nWe clearly detect the afterglow in stacked images (Stamatikos et al. GCN \n#9768, Cenko GCN #9769). Based on the first 4 min of total exposures, we \nestimate preliminary magnitudes and upper limits (all in AB system) of\n\ng' = 22.15 +- 0.15 mag,\nr' = 21.50 +- 0.08 mag,\ni' = 21.30 +- 0.13 mag,\nz' = 21.02 +- 0.12 mag,\nJ = 20.57 +- 0.15 mag,\nH > 19.8 mag,\nK > 18.9 mag\n\nThe given magnitudes are calibrated against SDSS as well as 2MASS field \nstars and are not corrected for the expected Galactic foreground extinction \ncorresponding to a reddening of E_(B-V)=0.02 mag in the direction of the \nburst (Schlegel et al. 1998).\n\nThe foreground extinction corrected spectral energy distribution is well \nfit with a pure power law and a spectral index of beta = 1.1+/-0.2 and no \nstrong evidence of excess extinction.\n\nThe flux difference between the g' band magnitude and the extrapolation of \nthe power law as defined by r'i'z'J is consistent with Lyman-alpha \nabsorption at a redshift of 2.45 as reported by de Ugarte Postigo et al. \n(GCN #9771).",
  "circularId": 9773,
  "createdOn": 1250078071000,
  "email": "kruehler@mpe.mpg.de",
  "subject": "GRB 090812: GROND Observations of the Optical/NIR Afterglow",
  "submitter": "Thomas Kruehler at MPE/MPI  <kruehler@mpe.mpg.de>",
  "eventId": "GRB 090812"
}