Analysis methods for gravitational wave from binary neutron star coalescences: investigation on the post-merger phase

The coalescence of binary neutron stars (BNS) is amongst the most promising sources for advanced gravitational wave (GW) detectors. The forthcoming addition of the advanced Virgo interferometer to the LIGO detector network will greatly improve the estimation of GW characteristics and therefore the capabilities to test features in the GW signal emitted by the coalescence of a NS binary. Such an observation can constrain the equation of state of these stars in at least two ways: by investigating smaller effects on top of the signal from the inspiral phase due to the tidal deformability of the components and by characterizing the emission from the possible highly excited NS remnant after the merger. Both methods promise to probe matter up to yet unknown and unexplored supranuclear densities, provided that the signal-to-noise ratio (SNR) at which the single GW is detected is sufficiently high or that the results from more detections can be combined together. Depending on mass and Equation of State (EoS) of the NS progenitors, the final fate of the merger can produce either a prompt collapse to black hole (BH) or a massive NS remnant. In the latter case, the merger remnant could be a short-lived, hypermassive NS (HMNS) collapsing to a BH within a few tens of ms after merger, or a long-lived NS, which in turn can be either supramassive (SMNS), i.e. collapsing to a BH on much longer timescales of order of seconds, or even a stable NS. These remnants will be highly excited, showing transient nonaxisymmetric deformations and quadrupolar oscillations, which are expected to emit GWs peaked in the frequency range around 2-3 kHz. The observation of these Post Merger (PM) fingerprints, would allow to constrain the EoS and at the same time to estimate combinations of stellar parameters, such as mass and radius of the two objects. With these motivations, my PhD thesis addressed the development of a new data analysis tool in order to investigate the GW signal emitted during the PM phase following a NS coalescence. The analysis procedure is developed inside the framework of the Coherent Wave Burst (cWB) pipeline which is employed by LIGO and Virgo collaboration to search for burst signals, i.e. it makes minimal assumption on the GW morphology and provides a robust coverage of generic GW transients.