The Gamma-Ray Burst Intrinsic Duration Distribution: Progenitor Insights across Cosmic Time
Annotatsiya
Abstract We present the distribution of the intrinsic duration of gamma-ray burst (GRB) emission. This expands upon the analysis of O. Bromberg et al. (2012, 2013), who showed evidence for collapsar progenitors based on the presence of a plateau in the distribution of T 90 , the duration over which 90% of the prompt emission is observed. We confirm the presence of this plateau in the distribution of duration corrected for cosmological time dilation but shifted to smaller timescales by a factor of 1/(1 + z av ) ∼ 1/3, where z av is the average GRB redshift. More significantly, we show that this plateau is only present in the sample of GRBs with redshifts greater than (1 + z ) ∼ 2. This result aligns with suggestions that the low-redshift population of GRBs has a significant contribution from noncollapsar progenitors (while the high-redshift sample is dominated by collapsars). We also show the difference in this distribution between spectrally hard and soft GRBs, confirming that a plateau is only present for the soft subset of GRBs. However, when we separate the soft GRBs into low- and high-redshift subsets, we find that only the high-redshift soft GRBs show evidence of a plateau, while the low-redshift soft GRBs do not. This suggests that there exists a significant subset of spectrally soft noncollapsar progenitors at low redshift . Finally, we use the end time of the plateau to constrain the GRB progenitor density profile and radius and show that the maximum size of a collapsar is a few tenths of a solar radius.