{
  "bibcode": "2006GCN..5597....1F",
  "body": "D.B. Fox (Penn State), A. Rau (Caltech), & E.O. Ofek (Caltech) report\non behalf of a larger collaboration:\n\n\"We have imaged the Swift XRT localization region for GRB060923A\n(Trigger 230662; Stamatikos et al., GCN 5583) with Keck-I + LRIS\n(I-band) and Gemini-North + NIRI (J- and K-band).  We identify the\ncandidate afterglow of Tanvir et al. (GCN 5587) in our K-band images\nas the only point source consistent with the XRT localization, with a\nbrightness estimated as follows:\n\n   K-band:  Ks~20.6 mag at 07:04 UT\n\nWe estimate its brightness (without correcting for Galactic\nextinction) by reference to the 2MASS star at R.A. 16:58:31.463,\nDec. +12:22:12.88 (J2000), which has J=15.175 mag, H=14.585 mag, and\nKs=14.457 mag in that catalog.\n\nThe position of the source by reference to NOMAD catalog sources in\nthe vicinity is:\n\n    R.A. 16:58:28.15, Dec. +12:21:38.9 (J2000)\n\nwith an estimated uncertainty of less than 0.5\" in each coordinate.\n\nThe source is undetected in our earlier J-band and I-band images.  Our\nupper limits on the brightness of the source in these bands are:\n\n   I-band:  I>23.5 mag at 06:11 UT\n   J-band:  J>23.7 mag at 06:42 UT\n\nThe I-band photometry is referenced to the SDSS imaging of this field\n(Cool et al., GCN 5585) while the J-band zero-point is derived from\nthe 2MASS star referenced above.  Magnitudes have not been corrected\nfor Galactic extinction.\n\nIf this source is the afterglow of GRB060923A, the red colors are\nsuggestive of a highly extinguished or high-redshift burst.  In\nparticular, correcting for the Schlegel, Finkbeiner & Davis (1998)\nestimate of E(B-V)=0.058 mag Galactic extinction, and assuming a\ntemporal decay of t^(-1) and an intrinsic afterglow spectrum of F_nu ~\nnu^(-1), these limits indicate suppression of the afterglow flux\n(relative to K-band) by a factor of >18 at 0.9 micron (I-band) and by\na factor of >14 at 1.23 micron (J-band).",
  "circularId": 5597,
  "createdOn": 1159035444000,
  "email": "dfox@astro.psu.edu",
  "subject": "GRB 060923A:  Keck and Gemini Observations",
  "submitter": "Derek Fox at PSU  <dfox@astro.psu.edu>",
  "eventId": "GRB 060923A"
}