The Durations and Spectral Hardness Ratios of Swift BAT Gamma-Ray Bursts in the Co-Moving Frame
Abstract
We have carefully determined the durations with error bars for 155 Swift BAT bursts with a uniform method. We experimented with two methods for transforming the hardness ratio from the observer frame to the co-moving frame. We present the hardness duration plot for 47 Swift bursts with known redshift in the observer frame and, for the first time, in the co-moving frame. We discuss a clear evolution with energy of the T90 durations in the overall populations of the short and long Swift bursts and derive the dividing times separating the short and long bursts in the four BAT energy bands. From Kolmogorov-Smirnov tests, we find that short and long Swift bursts and the short and long BATSE bursts are consistent with having been drawn from the same parent populations, provided that we introduce energy dependent scaling factors and adopt a lower efficiency of detection for short bursts for Swift BAT than for BATSE. With these scaling factors, we are able to continue the trend of decreasing durations in the overall populations of short and long bursts with increasing energy to include the set of BATSE bursts. Finally, we discuss the implications our conclusions have for understanding the nature of short and long gamma-ray bursts.
- Publication:
-
AAS/High Energy Astrophysics Division #9
- Pub Date:
- December 2006
- Bibcode:
- 2006HEAD....9.1370C