{
  "bibcode": "2009GCN..8771....1A",
  "body": "GRB 090102: GROND observations of the optical afterglow \n\n\nP. Afonso, T. Kruehler (both MPE Garching), S. Klose (TLS Tautenburg), and \nJ. Greiner (MPE Garching) report on 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),started observations of the field \nof GRB 090102 (Mangano et al. 2008, GCN #8762) in g'r'i'z'JHK at 05:25 UTC, \n2.50 h after the burst. \n\nPreliminary photometry yields the following r' band magnitudes of the \noptical afterglow (Klotz et al., GCN #8761, and also GCNs #8762, #8763, \n#8764, #8766 and #8770), calibrated against SDSS field stars. \n\nT_mid[s]  Exp[s] AB Mag  MagErr\n -------------------------------\n9042      66     20.58   0.05\n9158      66     20.59   0.04\n9265      66     20.58   0.03\n9373      66     20.59   0.06\n9515      115    20.59   0.04\n9711      115    20.65   0.02\n9903      115    20.67   0.02\n10091     115    20.66   0.03\n10423     375    20.70   0.02\n10868     375    20.78   0.02\n11320     375    20.79   0.02\n11780     375    20.86   0.02 \n\nThe quoted error is statistical only. There is an additional systematic \nerror in the absolute calibration using SDSS field stars which is expected \nto be in the 0.05 mag range. \n\nIn this time interval, the light curve is well described with a single power \nlaw of index 1.0 +/- 0.1, compatible with the value reported by Curran et \nal. (GCN #8770). Comparing against the early TAROT data (Klotz et al., GCN \n#8764), this indicates a flattening of the light curve. If the afterglow \ncontinues to decline with this power law, we predict r' band magnitudes of \n~23.1 at 1 day and ~24.3 at 3 days after the burst. \n\nAfter correcting for a Galactic foreground extinction corresponding to a \nreddening of E_(B-V)=0.05 (Schlegel et al. 1998), the g' to K band SED is \nwell described with a power law of spectral index beta = 1.0 +- 0.2.",
  "circularId": 8771,
  "createdOn": 1230940745000,
  "email": "pafonso@mpe.mpg.de",
  "subject": "GRB 090102: GROND observations of the optical afterglow",
  "submitter": "Paulo M. J. Afonso at MPE  <pafonso@mpe.mpg.de>",
  "eventId": "GRB 090102"
}