Observation of the central engine of GRB170817A: the spin-down of a Kerr black hole based on multimessenger calorimetry and event timing

The central engine of GRB170817A is probed by a contemporaneous descending chirp in gravitational radiation in model-agnostic spectrograms with equal sensitivity to ascending and descending chirps using time-symmetric butterfly matched filtering, calibrated by software injection experiments. Statistical significance is expressed by probabilities of false alarm (PFA; type I errors) derived from event-timing analysis on the start-time $t_s$. PDF($t_s$)s are identified by high-resolution image analyses of the available spectrograms. For merged (H1,L1)-spectrograms, a PFA $p_1$ derives from causality given GW170817-GRB17081A. A statistically independent confirmation is presented in individual H1 and L1 analyses, in a second PFA $p_2$ of consistency in their respective observations of $t_s$ . A combined PFA derives from their product since mean and (respectively) difference in timing are statistically independent. PFAs in event timing thus produce $p_1 = 8.3 imes 10^{-4}$ and $p_2 = 4.9 imes 10^{-5}$ for the output ${cal E}_GW simeq 3.5\%M_odot c^2$ ($p_1p_2 = 4.1 imes 10^{-8}$ , equivalent Z-score 5.48). ${cal E}_GW$ exceeds $E_J$ of the hyper-massive neutron star in the immediate aftermath of GW170817, yet it is consistent with $E_J$ rejuvenated in delayed gravitational collapse to a Kerr black hole. Similar results may apply to energetic core-collapse supernovae. (van Putten, M.H.P.M., & Della Valle, M., 2022, A&A, in press, https://doi.org/10.1051/0004-6361/202142974.)