Based on the early-year observations from Neil Gehrels Swift Observatory , [ Liang et al .
( 2007 ) ] 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 } , \Gamma _ { X, 1 } , and \alpha _ { X, 1 } ) still accords with normal or lognormal distribution ; 2 ) \Gamma _ { X, 1 } and \Gamma _ { \gamma } 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 ^ { \prime } _ { b } disappears , so that the global 3-parameter correlation ( E _ { iso,X } - E ^ { \prime } _ { p } - t ^ { \prime } _ { b } ) becomes less significant ; 6 ) the anti-correlation between L _ { X } and t ^ { \prime } _ { b } and the three-parameter correlation ( E _ { iso, \gamma } - L _ { X } - t _ { b } ) indeed exist with a high confidence level .
Overall , our results are generally consistent with [ Liang et al .
( 2007 ) ] , 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 .