Peak-to-peak dilation of Gamma Ray Bursts

If Gamma Ray Bursts are at cosmological distances, then the faint bursts must have light curves which are stretched in time when compared to bright bursts. Such a time dilation has been reported by Norris and coworkers, where the relative stretching of pulse durations is roughly a factor of two between bright and faint burst. Nevertheless, models have been presented which can account for this peak-duration dilation within galactic models. A solution to this ambiguity can be had by looking for dilation of different measures of time scale, as these would not be subject to the same effects. One such time scale is the peak-to-peak time. Cosmological models can only be true if the peak-to-peak dilation agrees exactly with the peak-duration dilation. This is a sharp test. In this paper, we report on our study of peak-to-peak dilation of 465 multipeaked bursts from the BATSE 2B catalog. We used a wide variety of peak selection criteria and peak-to-peak time scale definitions. We find that many tests can find dilations with a factor of two, yet that many other tests can prove that there is no dilation. That is, by selecting which test to adopt, we can make peak-to-peak dilation either appear or disappear at high levels of significance. We conclude that the measurement of dilation has subtle systematic errors of unknown nature, and these can only be recognized by detailed Monte Carlo analyses.