2019/08/05 by Litao Zhao, Binbin Zhang, He Gao +3 · 1 citation
Physics and Astronomy · #astro-ph.HE
paper · pdf · doi:10.3847/1538-4357/ab38c4
accepted for publication by ApJ
arxiv created 2019/08/05 · arxiv updated 2019/10/02
Based on the early-year observations from Neil Gehrels Swift Observatory, \citeliang07 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. tb , SX, ΓX,1, and αX,1) still accords with normal or lognormal distribution; 2) ΓX,1 and Γγ 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)=L0(\fractt0)-q, we find that the value q is mainly distributed between -0.5 and 0.5, with an average value of 0.16± 0.12; 5) the tentative correlation between E_\rmiso,X and t'b disappears, so that the global 3-parameter correlation (E_\rmiso,X-E'p-t'b) becomes less significant; 6) the anti-correlation between LX and t'b and the three-parameter correlation (E_\rmiso,γ-LX-tb) indeed exist with a high confidence level. Overall, our results are generally consistent with \citeliang07, 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.