{
  "bibcode": "1999GCN...214....1F",
  "body": "E. Falco, C. Petry, C. Impey, A. Koekemoer, and J. Rhoads report on behalf\nof the KPNO GRB Followup team:\n\nFalco, Petry, and Impey have observed the optical counterpart of GRB 990123\nin U band on 1999 January 24.497 UT using the 4 meter Mayall telescope and\nCCD Mosaic Camera at Kitt Peak National Observatory.  Conditions were\nnon-photometric with 1.3 arcsecond seeing.\n \nThe counterpart (cf. Odewahn et al, GCN 201) is clearly detected.  Absolute\nflux calibration is not yet possible, but the transient is approximately\n1.1 magnitude fainter than the reference object at position RA=15:25:32.7,\ndec=+44:44:29.7 (J2000).  The statistical uncertainty in the flux\nshould be of order 3%.  The counterpart is a point source in our data,\nsuggesting that host galaxy flux contributes only a small fraction of\nthe current U band brightness.  We suggest that the afterglow may be bluer\nthan the host galaxy; if so, U band would be a good wavelength to follow\nits light curve to late stages.\n \nIn addition, Koekemoer has observed the counterpart at K band on 1999\nJanuary 24.546 UT using the 2.1 meter telescope and ONIS near-infrared\ncamera at Kitt Peak National Observatory.  Total exposure time was 600\nseconds.  The transient is not readily apparent in the coadded image.\nThe rough limiting magnitude of the K band image can be estimated from\nthe USNO-A1 catalog, which gives Red and Blue magnitudes 14.4 and 15.5\nfor a star with signal to noise ratio 10 in the combined K band image.\nMore careful processing might improve this limit modestly.\nCombining these two measurements will yield a limit on the spectral slope\nof the afterglow.\n \nA section of the U band image is available at\nhttp://www.noao.edu/noao/grb/990123.html .\n \nThis report is citable.",
  "circularId": 214,
  "createdOn": 917227813000,
  "email": "rhoads@noao.edu",
  "subject": "GRB 990123 optical observations",
  "submitter": "James Rhoads at KPNO  <rhoads@noao.edu>",
  "eventId": "GRB 990123"
}