SPECTRAL EVOLUTION OF GAMMA-RAY BURSTS DETECTED BY THE SIGNE EXPERIMENT .1. CORRELATION BETWEEN INTENSITY AND SPECTRAL HARDNESS

We study the continuum spectral evolution of 16 gamma-ray bursts detected by the France-Soviet SIGNE experiment in 1981-1982 by fitting time resolved (0.5 s) spectra in count space with simple thermal bremsstrahlung and synchrotron models. We find that there is no single characteristic of spectral evolution: we see hard-to-soft, soft-to-hard, luminosity-hardness tracking, and chaotic evolution. We perform correlation studies between instantaneous burst intensity and spectral temperature for seven bursts. While we basically confirm the existence of a correlation between these variables as originally claimed by Golenetskii et al. (1983) we find higher values and a broader range of correlation indices.