The shallow decay segment of GRB X-ray afterglow revisited

Litao Zhao; Binbin Zhang; He Gao; Lin Lan; Houjun Lü; Bing Zhang

doi:10.3847/1538-4357/ab38c4

paper

The shallow decay segment of GRB X-ray afterglow revisited

arXiv:1908.01561 · doi:10.3847/1538-4357/ab38c4

Abstract

Based on the early-year observations from Neil Gehrels \emph{Swift} Observatory, \cite{liang07} performed a systematic analysis for the shallow decay component of gamma-ray bursts (GRBs) X-ray afterglow, in order to explore its physical origin. Here we revisit the analysis with an updated sample (with Swift/XRT GRBs between February 2004 and July 2017). We find that with a larger sample, 1) the distributions of the characteristic properties of the shallow decay phase (e.g. $t_{b}$ , $S_{X}$ , $Γ_{X, 1}$ , and $α_{X, 1}$ ) still accords with normal or lognormal distribution; 2) $Γ_{X, 1}$ and $Γ_{γ}$ still show no correlation, but the tentative correlations of durations, energy fluences, and isotropic energies between the gamma-ray and X-ray phases still exist; 3) for most GRBs, there is no significant spectral evolution between the shallow decay segment and its follow-up segment, and the latter is usually consistent with the external-shock models; 4) assuming that the central engine has a power-law luminosity release history as $L (t) = L_{0} (\frac{t}{t _{0}})^{- q}$ , we find that the value $q$ is mainly distributed between -0.5 and 0.5, with an average value of 0.16 $\pm$ 0.12; 5) the tentative correlation between $E_{iso, X}$ and $t_{b}^{'}$ disappears, so that the global 3-parameter correlation ( $E_{iso, X} - E_{p}^{'} - t_{b}^{'}$ ) becomes less significant; 6) the anti-correlation between $L_{X}$ and $t_{b}^{'}$ and the three-parameter correlation ( $E_{iso, γ} - L_{X} - t_{b}$ ) indeed exist with a high confidence level. Overall, our results are generally consistent with \cite{liang07}, confirming their suggestion that the shallow decay segment in most bursts is consistent with an external forward shock origin, probably due to a continuous energy injection from a long-lived central engine.

arXiv commentaccepted for publication by ApJ

The shallow decay segment of GRB X-ray afterglow revisited

Abstract

References in corpus (71)

Cited by in corpus (24)