Temporal and spectral characteristics of short bursts from the soft gamma repeaters 1806-20 and 1900+14

We study the temporal and coarse spectral properties of 268 bursts from SGR 1806-20 and 679 bursts from SGR 1900 + 14, all observed with the Rossi X-Ray Timing Explorer/Proportional Counter Array. Hardness ratios and temporal parameters, such as T-90 durations and iota (90) emission times are determined for these bursts. We find a lognormal distribution of burst durations, ranging over more than 2 orders of magnitude: T-90 similar to 10(-2) to greater than or similar to 1 s, with a peak at similar to 0.1 s. The burst light curves tend to be asymmetrical, with more than half of all events showing rise times t(r) < 0.3 T-90. We find that there exists a correlation between the duration and fluence of bursts from both sources. We also find a significant anticorrelation between hardness ratio and fluence for SGR 1806-20 bursts and a marginal anticorrelation for SGR 1900 + 14 events. Finally, we discuss possible physical implications of these results within the framework of the magnetar model.