Observations of GRB 990123 by the Compton Gamma Ray Observatory

Academic Article


  • GRB 990123 was the first burst from which simultaneous optical, X-ray and gamma-ray emission was detected; its afterglow has been followed by an extensive set of radio, optical and X-ray observations. We have studied the gamma-ray burst itself as observed by the CGRO detectors. We find that gamma-ray fluxes are not correlated with the simultaneous optical observations, and the gamma-ray spectra cannot be extrapolated simply to the optical fluxes. The burst is well fit by the standard four-parameter GRB function, with the exception that excess emission compared to this function is observed below ~15 keV during some time intervals. The burst is characterized by the typical hard-to-soft and hardness-intensity correlation spectral evolution patterns. The energy of the peak of the nu f_nu spectrum, E_p, reaches an unusually high value during the first intensity spike, 1470 +/- 110 keV, and then falls to \~300 keV during the tail of the burst. The high-energy spectrum above ~MeV is consistent with a power law with a photon index of about -3. By fluence, GRB 990123 is brighter than all but 0.4% of the GRBs observed with BATSE, clearly placing it on the -3/2 power-law portion of the intensity distribution. However, the redshift measured for the afterglow is inconsistent with the Euclidean interpretation of the -3/2 power-law. Using the redshift value of >= 1.61 and assuming isotropic emission, the gamma-ray fluence exceeds 10E54 ergs.
  • Authors

  • Briggs, MS
  • Band, DL
  • Kippen, RM
  • Preece, RD
  • Kouveliotou, C
  • van Paradijs, J
  • Share, GH
  • Murphy, RJ
  • Matz, SM
  • Connors, A
  • Winkler, C
  • McConnell, Mark
  • Ryan, JM
  • Williams, OR
  • Young, CA
  • Dingus, B
  • Catelli, JR
  • Wijers, RAMJ
  • Status

    Publication Date

  • October 10, 1999
  • Has Subject Area


  • X-rays : bursts
  • gamma rays : bursts
  • Digital Object Identifier (doi)

    Start Page

  • 82
  • End Page

  • 91
  • Volume

  • 524
  • Issue

  • 1