Pulse-resolved Classification and Characteristics of Long-duration Gamma-Ray Bursts with Swift-BAT Data. II. Main Bursts versus Extended Emissions

Long gamma-ray bursts (GRBs) frequently exhibit complex prompt-emission morphology, including a bright main-emission (ME) episode followed by a weaker extended-emission (EE) component. Whether these subcomponents are produced by the same central engine under different physical conditions remains unclear. Here, we present a systematic, pulse-resolved analysis of 24 Swift Burst Alert Telescope (BAT) long-duration GRBs that exhibit a well-separated ME episode ( G 1 ) followed by a fainter EE episode ( G 2 ) after a background-consistent quiescent interval. For each episode, we measure the episode-only duration ( T 90 ), count-based hardness ratio, minimum variability timescale (MVT), and spectral lag using the same Swift-BAT analysis pipeline adopted in Paper I. We find that the EE is typically softer and smoother than the ME: HR EE < HR ME in 20 of 24 events, and MVT EE > MVT ME in 19 of 24 events. The EE also shows a broader lag distribution, including both large positive and negative lags, although the sample-wide median lag offset is not statistically significant. Both episodes remain in the long-GRB track in the duration–hardness and duration–MVT planes. These results suggest that the EE in long GRBs may represent a physically distinct regime of the central engine, characterized by a lower luminosity, longer emission timescales, and softer spectral properties, rather than a simple continuation of the main burst. The observed trends are consistent with late-time central engine activity, such as fallback accretion onto a black hole or protomagnetar spin-down.