THE ENERGY S PECTRA OF G AMMA-RAY B URSTS: O LD PUZZLES, RECENT ANALYSIS AND N EW RESULTS

Gamma-ray burst spectroscopy has at times been thought of as the key to understanding these mysterious events, and at others as a source of disappointment and confusion. Early spectral measurements contained evidence for cyclotron-line-like absorp- tion and emission features. These results were the main anchor for the galactic neutron star paradigm for the origin of gamma-ray bursts. Ginga provided striking confirmation with evidence in three bursts for cyclotron absorption with both first and second harmon- ics present. The absorption line energies were consistent with the teragauss magnetic fields expected for neutron stars. The BATSE experiment on CGRO has dealt a severe blow to this paradigm. BATSE has found no evidence for the expected galactic anlsotropy and also no evidence for cyclotron lines. The exact degree of inconsistency between BATSE and earlier GRB line results remains a complicated and unresolved question. In general, burst spectra display a wide variety of both spectral and temporal behavior. In essential- ly all bursts where spectral measurements are possible, the spectrum evolves during the burst. This spectral complexity and variability has presented researchers with a challeng- ing task. At the present time, only the broadest correlations and characterizations are in hand. This paper will; 1) give a brief historical overview of GRB spectroscopic measure- ments and 2) provide a summary of the current observational situation with emphasis on the BATSE/Ginga controversy.