A Variety of Decays of Gamma-Ray Burst Pulses

Abstract.

The main target of this study is the GRB light curve during the decay phase of long, bright pulses. As shown by Ryde & Svensson (2000; hereafter RS00) approximately half of these decays can be described by a power law $\propto 1$/(time). This happens for cases when the hardness-fluence correlation (HFC) is an exponential function, $E_{\rm pk}(\Phi) \propto e^{-\Phi/\Phi_0}$, and the hardness-intensity correlation (HIC) is a power law, $E_{\rm pk}(N) \propto (N/N_0)^{\delta}$. Here, N(t) is the instantaneous photon flux, $E_{\rm pk}(t)$ is the corresponding photon energy, at which the $E^2 N_{\rm E}$-spectrum peaks and is used as a measure of the spectral hardness, and the photon fluence is defined by $\Phi(t) = \int^t N(t') dt'$. These most commonly assumed correlations were found by Liang & Kargatis (1996; HFC) and Golenetskii et al. (1983; HIC).