{
  "bibcode": "1999GCN...240....1B",
  "body": "GRB 990123:  Detection of the IR Transient, and the Light Curve Fits\n\nJ. S. Bloom, C. Koresko, S. R. Kulkarni,  S. G. Djorgovski, R. R. Gal, \n      and S. C.  Odewahn,  Caltech,\nH. I. Teplitz, NASA Goddard Space Flight Center,\nD. Koerner, Univ. of Pennsylvania,\nD. Kirkpatrick, Infrared Processing and Analysis Center,\nM. A. Malkan, and I. S. McLean, Univ. of California, LA,\nD. A. Frail, National Radio Astronomy Observatory, \nreport on behalf of the Caltech-CARA-NRAO GRB collaboration:\n\n\"The field of the optical transient of GRB 990123 (GCN 201) was observed\nwith the Near Infra-red Camera (NIRC) on the Keck I telescope on\n24 January 1999 UT by Koerner and Kirkpatrick.  We report the discovery\nof the IR counterpart of the afterglow with K = 18.3 +/- 0.03 mag (epoch \n24.6356 Jan 1999 UT).   The same field was observed by Malkan, Teplitz and\nMcLean on the nights of January 27.65 and 28.55 UT, and in both instances\nthe object was readily detected.  Fitting a power law to the three\nmagnitudes yields a power law exponent of alpha_K= -1.14 +/- 0.08.\n\nSeparately, we have carried out a program of recalibrating Gunn r and R \nband magnitudes reported by others via the GCN.  We used those measurements\nwhich reported the magnitude of a reference star (or stars) and have put all \nthe measurements on a common photometric system. A fit to these recalibrated \nmagnitudes yields a power law slope, alpha_r = -1.13 +/- 0.03.  Within \nerrors, the slope of the K band data is fully consistent with that obtained \nfrom the r/R band data. We adopt a mean alpha of -1.13.\n\nThe color difference between the decaying r and K fluxes is (r-K) = 2.75 mag. \nConverting the magnitudes to flux this color difference corresponds to \nbeta = -0.82, where f_nu = const * nu^beta.  The ratio alpha/beta = 1.38. \nThis suggests that the cooling frequency is higher than the central frequency \nof the r band (about 4x10^14 Hz) even two days after the burst.  We urge \ncontinued monitoring of the optical transient in the r/R band with the view \nof detecting the passage of the cooling break.\n\nIn contrast to the light curves measured in the r and K bands, the light\ncurve in the B band (calibrated on a uniform photometric system) is not well \ndescribed by a power law.  The origin of this discrepancy is as yet unclear.\nFurther observations are in progress.\n\nThis report is citeable.\"",
  "circularId": 240,
  "createdOn": 917584281000,
  "email": "george@oracle.caltech.edu",
  "subject": "GRB 990123:  Detection of the IR Transient, and the Light Curve Fits",
  "submitter": "George Djorgovski at Caltech/Palomar  <george@oracle.caltech.edu>",
  "eventId": "GRB 990123"
}