van Putten, Maurice H. P. M.Maurice H. P. M.van PuttenDELLA VALLE, MassimoMassimoDELLA VALLE2021-04-092021-04-0920190035-8711http://hdl.handle.net/20.500.12386/30727The recent LIGO event GW170817 is the merger of a double neutron star system with an associated short GRB170817A with 2.9 ± 0.3 s soft emission over 8-70 keV. This association has a Gaussian equivalent level of confidence of 5.1σ. The merger produced a hypermassive neutron star or stellar mass black hole with prompt or continuous energy output powering GRB170817A. Here, we report on a possible detection of extended emission (EE) in gravitational radiation during GRB170817A: a descending chirp with characteristic time-scale τ_s=3.01± 0.2 s in a (H1,L1)-spectrogram up to 700 Hz with Gaussian equivalent level of confidence greater than 3.3σ based on causality alone following edge detection applied to (H1,L1)-spectrograms merged by frequency coincidences. Additional confidence derives from the strength of this EE. The observed frequencies below 1 kHz indicate a hypermassive magnetar rather than a black hole, spinning down by magnetic winds and interactions with dynamical mass ejecta.STAMPAenArticle10.1093/mnrasl/sly1662-s2.0-85057142122https://academic.oup.com/mnrasl/article/482/1/L46/50904252019MNRAS.482L..46VFIS/05 - ASTRONOMIA E ASTROFISICA