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tokens: conceivably due to dynamical mass ejecta. Colour coding (blue-to-yellow) is proportional to amplitude defined by butterfly output ρ of time-symmetric chirp-like template correlations to data. Fig. 2 shows a continuation of GW170817 with a long-duration descending chirp during GRB170817A. It can be fitted by an exponential track ( Supplementary Information ) with s, t s = 1843.1 s, Hz, and f 0 = 98 Hz. Crucially, s shows the descending chirp to start in the 1.7 s gap between GW170817 and GRB170817A, satisfying the aforementioned causality condition. A Gaussian equivalent level of confidence greater than 3.3σ obtains for significance to the central engine of GRB170817A based on causality over 1952 s of LIGO data. Improved estimates obtain upon including the statistical significance of the strength of the signal ( Supplementary Information ). The estimated initial frequency Hz at the time of coalescence inferred from ( 2 ) is below the orbital frequency at which the stars approach the Inner Most Stable Circular Orbit (ISCO) of the system as a whole, i.e. Hz at km according to the Kerr metric (Kerr 1963 ; Bardeen, Press Teukolsky 1972 ; Shapiro Teukolsky 1983 ). At this point, a binary system of two equal mass neutron stars would have a rotational energy and a dimensionless specific angular momentum . While this allows prompt collapse to an Kerr black hole (Kerr 1963 ) any gravitational-radiation from remaining debris orbiting about the ISCO would be above 2 kHz. Instead, the 1kHz descending chirp in Fig. 2 points to radiation of from a long-lived rapidly rotating hypermassive neutron star or magnetar with a dimensionless quadrupole moment of , where R is the radius of the star, induced by dynamical and secular instabilities (Owen et al. 1998 ; Kokkotas 2008 ; Corsi Mészáros 2009 ) that may include magnetic fields (Cutler 2002 ; Abbott et al. 2017d ). Magnetar spin down indicated by the descending chirp may include magnetic interactions with surrounding matter from dynamical mass ejections from the preceding merger, in addition to gravitational radiation losses alone. These ejecta are commonly found in aforementioned numerical simulations. The interactions may result from magnetic coupling (Gosh, Pethick Lamb 1977 ; Gosh Lamb 1978 , 1979 ) and/or tidal stresses (Hotokezaka et al. 2013 ) that may include magnetic outflows from open field lines (Lovelace, Romanova Bisnovatyi-Kogan 1995 ; Parfrey, Spitkovksy Beloborodov 2016 ) and gravitational-wave emission from quadrupole moments in orbiting debris. While the descending chirp identifies the central energy reservoir of GRB170817A to be a rotating hypermassive neutron star or magnetar, its connection to GRB170817A remains uncertain. Perhaps the relatively soft second gamma-ray pulse of GRB170817A (Pozanenko et al. 2018 ) derives from outflows from debris orbiting the star, while the short-hard pulse derives from an initial outflow from the star at birth. More likely, the complex spectral evolution of