Extended Emission in Short Gamma-Ray Bursts: Energy and Duration Constraints on the Remnant

About a quarter of short gamma-ray bursts show softer extended emission lasting tens to a hundred seconds after the initial spike. That duration exceeds the dynamical time of a black hole accretion disk and points to a longer-lived engine. This paper compares the radiated energies and durations with magnetar spin-down and disk lifetimes. Using the calculation described in the Methods, the headline results are: typical_mean_L_erg_s = 6.25e+48, total_EE_range_erg = [5e+49, 2e+51], max_duration_s = 100. The duration argument favours a surviving magnetar remnant for the extended-emission class, while the energy argument alone would not, because beamed disk energies can be stretched to fit. Events whose extended emission exceeds the magnetar rotational cap remain problematic for both engines and are flagged individually rather than averaged away. This study is simulated and computed from stated assumptions; it is not a measurement. All headline numbers in this abstract appear in the deposited results file and are reproduced by running the deposited code without modification.