{
  "bibcode": "2009GCN..8850....1R",
  "body": "A. Rossi (Tautenburg Obs.), T. Kruehler, J. Greiner and F. Olivares \n(all MPE Garching), report on behalf of the GROND team:\n\nWe report on further analysis and new observations of the optical afterglow \ncandidate of GRB 090118 (Copete et al. 2009, GCN #8825).\n\nWe re-analyzed our first epoch images (Olivares et al. 2009, GCN Circ. 8826),\ntaken at about 11 hrs after the GRB. No source is seen in our NIR images at \nthe position of the X-ray afterglow (Rowlinson et al. 2008, GCN Circ. 8828),\ngiving upper limits (Vega system) of \n\nJ > 20.6 \nH > 19.6  \nK > 18.7  \n\ncalibrated against 2MASS field stars.\n\nThe XRT position (Rowlinson et al. 2009, GCN  Circ. 8828) is outside of the \nfield-of-view of the g'r'i'z' detectors, so no statement can be made on\nthe optical brightness during our first epoch.\n\nWe observed the field of GRB 090118 again with GROND on 2009-01-22 at a\nmid-time of 01:30 UTC, about 100 hours after the burst. We clearly detect \nthe candidate mentioned by Updike and Hartmann (2009, GCN Circ. 8829) in \nour optical filters, but not in the NIR:\n\ng'= 23.46 +- 0.11 (AB)\nr'= 23.27 +- 0.10 (AB)\ni'= 22.95 +- 0.12 (AB)\nz'= 22.25 +- 0.14 (AB)\nJ > 21.5 (Vega)\nH > 20.5 (Vega)\nK > 19.6 (Vega)\n\nNo correction for the foreground extinction of E(B-V)=0.135 mag\nhas been applied.\n\nComparing our g'r'i'z' values with the J and H detections of Updike & Hartmann \n(2009a; GCN Circ. 8829) and Minowa et al. (2009; GCN Circ. 8832) about two\ndays earlier, we find that the spectral energy distribution is smooth, thus \nsupporting the non-fading nature of this object as indicated already by the\nresults of Updike & Hartmann (2009b; GCN Circ. 8831) and Minowa et al. \n(2009; GCN Circ. 8832).\n\nThe detection in g'r'i'z' implies that the object, whatever its nature, \nis at a redshift smaller than 3.5.\n\nThis excludes the possibility that this object is at high redshift and\nexhibited a long plateau phase. The plateau phase would have to last more \nthan 3 days in the NIR range, while at X-rays a steady decline has been \nseen (Rowlinson & Page 2009, GCN Circ. 8840). We conclude that this object \nis very likely not the optical/NIR afterglow of GRB 090118. Instead, the\nobject's SED is consistent with a low-redshift galaxy.",
  "circularId": 8850,
  "createdOn": 1232824987000,
  "email": "jcg@mpe.mpg.de",
  "subject": "GRB 090118: no afterglow candidate",
  "submitter": "Jochen Greiner at MPI  <jcg@mpe.mpg.de>",
  "eventId": "GRB 090118"
}