Observations of GRB 990123 by the Compton Gamma Ray Observatory

Authors

M S. Briggs, University of Alabama - Huntsville
D L. Band, University of California - San DiegoFollow
R M. Kippen, University of Alabama - HuntsvilleFollow
R D. Preece, University of Alabama - Huntsville
C Kouveliotou, Universities Space Research Association
J Van Paradijs, University of Alabama - Huntsville
G H. Share, National Research Laboratory
R J. Murphy, National Research Laboratory
S M. Matz, Northwestern University
A Connors, Wellesley CollegeFollow
C Winkler, ESTECFollow
Mark L. McConnell, University of New Hampshire - Main CampusFollow
James M. Ryan, University of New HampshireFollow
O R. Williams, ESTECFollow
C A. Young, University of New Hampshire - Main CampusFollow
B L. Dingus, University of UtahFollow
J R. Catelli, Goddard Space Flight Center
R Wijers, SUNY Stony Brook

Abstract

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 Compton Gamma Ray Observatory detectors. We find that gamma-ray fluxes are not correlated with the simultaneous optical observations and that the gamma-ray spectra cannot be extrapolated simply to the optical fluxes. The burst is well fitted by the standard four-parameter GRB function, with the exception that excess emission compared with 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 f 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 1 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 - power-law portion of the intensity distribution. However, the redshift measured for the afterglow is inconsistent with the Euclidean interpretation of the - power law. Using the redshift value of 1.61 and assuming isotropic emission, the gamma-ray energy exceeds 10⁵⁴ ergs.

Department

Space Science Center, Physics

Publication Date

10-10-1999

Journal Title

The Astrophysical Journal

Publisher

The American Astronomical Society

Digital Object Identifier (DOI)

10.1086/307808

Document Type

Article

Recommended Citation

Briggs, M S.; Band, D L.; Kippen, R M.; Preece, R D.; Kouveliotou, C; Van Paradijs, J; Share, G H.; Murphy, R J.; Matz, S M.; Connors, A; Winkler, C; McConnell, Mark L.; Ryan, James M.; Williams, O R.; Young, C A.; Dingus, B L.; Catelli, J R.; and Wijers, R, "Observations of GRB 990123 by the Compton Gamma Ray Observatory" (1999). The Astrophysical Journal. 39.
https://scholars.unh.edu/ssc/39

Rights

© 1999. The American Astronomical Society. All rights reserved. Printed in U.S.A.