A further study of $t_{\mathrm{burst}}$ of GRBs: rest frame properties, external plateau contributions and multiple parameter analysis

Abstract

[Zhang 2014] propose to redefine the true GRB central engine activity duration, $t_{\mathrm{burst}}$, by considering the contributions from the prompt $\gamma$-ray emission, X-ray flare and internal plateau features. With a comprehensive study on a large sample of Swift GRBs, it is shown that the $t_{\mathrm{burst}}$ distribution in the observer frame consists of a bimodal feature, suggesting the existence of a new population of ultra-long GRBs. In this work, we make a series of further studies on $t_{\mathrm{burst}}$: we update the Swift GRB sample up to June 2016; we investigate the properties of $t_{\mathrm{burst}}$ distribution in the rest frame; we redefine $t_{\mathrm{burst}}$ by involving external plateau contributions; we make a multiple parameter analysis to investigate whether the bursts within the ultra-long population being statistically different in sense of other features besides the duration distribution. We find that for all situations, the distribution of $t_{\mathrm{burst}}$ requires two normal distributions in logarithmic space to provide a good fit, both in observer frame and rest frame. Considering the observational gap effect would not completely erase the bimodal distribution feature. However the bursts within the ultra-long population may have no statistically different in sense of other features besides the duration term. We thus suggest that if the ultra-long population of GRBs indeed exists, their central engine mechanism and radiation mechanism should be similar to the normal population, but they have longer central engine activity timescale.

Accepted for publication in ApJ

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Cited by in corpus (1)

• External Shock in a Multi-Bursting Gamma-ray Burst: Energy Injection Phase induced by the Later Launched Ejecta