2025ApJ...993..147C

GRB 240619A, detected by Fermi-Gamma-ray Burst Monitor with a duration of ∼36.1 s at redshift z = 0.3965, a short, hard main emission (ME), a quiescent interval, and a soft extended emission (EE). We perform a detailed analysis of the temporal and spectral properties of both phases using Bayesian inference and machine learning techniques. Our main results show: (1) the spectral lags are 0.27 ± 0.03 s (ME) and 0.13 ± 0.19 s (EE), with the ME phase following the lag-luminosity relation; (2) The minimum variability timescales are ∼0.04 s (ME) and ∼0.48 s (EE), consistent with short gamma-ray bursts (SGRB) and long gamma-ray bursts (LGRB) characteristics, respectively, suggesting that the radiation in the two phases may originate from different physical mechanisms. (3) the effective amplitude f_eff ≈ 3.18 suggests an intrinsic origin consistent with SGRBs; (4) the spectral hardness, peak energy, Amati/Yonetoku relations, and energy-hardness-duration classification indicate that the ME phase is more similar to SGRBs, while the EE phase resembles LGRBs; (5) the local event rate density ($4.6{6}_{-3.86}^{+11.25}\times 1{0}^{-3}$ Gpc^–3 yr^–1) further highlights its peculiarity. Spectral analysis indicates that its nonthermal emission can be well explained by the fast-cooling synchrotron radiation model. Curvature effect analysis suggests jet acceleration in the EE phase, with the jet becoming Poynting-flux dominated. The combined evidence suggests that GRB 240619A is an SGRB with EE, likely originating from a compact binary merger, and exhibiting physical properties similar to those of GRB 211211A.