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The Rossby-Wave Instability (RWI) has been proposed to be at the origin of the highfrequency QPOs observed in black-hole systems. Here we are presenting the first full GR simulations of the instability around a Kerr black-hole which allow us to explore the impact of the spin on the instability. Those simulations, coupled with a full GR ray-tracing, allow us to directly compare our simulation with the observables we get through X-ray observations.

With NICER up and running and the ATHENA mission in preparation there is need to study in more detail what is the influence, if any, of the spin on the observed spectrum. Using the newly developed NOVAs framework which is comprised of a GR code, GRAM-RVAC, coupled with the ray-tracing GR code, gyoto, we computed a series of simulated disk spectrums for a variety of black-hole spins. Using standard models from xspec we fitted those spectrums and looked at how they performed to give us the parameters of the simulated spectrums. Here we report on our findings and how we could improve the existing models to get better insights into the physical large scale disk parameters.

Here we are presenting NOVAs, a Numerical Observatory of Violent Accreting systems, which couples a GR AMR MPI fluid dynamics code (GRAMRVAC) able to follow accretion around a Kerr Black-hole with the ray-tracing code GYOTO. Together, they allow us to test different models by running the simulation and obtaining spectral energy distributions and power-density spectrums from which we can extract the same observables as for ‘real’ observations, hence making it a Numerical Observatory.

Among the sources of gravitational waves worth modelling there are Extreme Mass Ratio binaries. In order to understand the dynamics during their coalescence, we describe a special class of ballistic geodesics in Schwarzschild space-time. These orbits are in 1-1 correspondence with stable circular orbits. From these special orbits we derive analytic expressions for the source terms in the Regge-Wheeler radiative equations for a point-particle, and compute the gravitational waves emitted during the infall in an Extreme Mass Ratio black-hole binary coalescence. Results of these calculations and the waveforms obtained are then discussed, showing limits and applicability of the method, among which the recognition of a universal geodetic behaviour in the last phase of plunge.

The inference of binary parameters from gravitational waves (GW) is one of the key science goals of the collaboration operating the advanced ground-based LIGO-Virgo detector network. We employ reduced order quadratures (ROQs) to substantially reduce the size of large inner products arising in Bayesian parameter estimation (PE) and thus enable studies of the GWs emitted by coalescences of spinning stellar mass black hole binaries approaching the full design sensitivity of these detectors. We build the first ROQs that include the inspiral, merger and ringdown parts of the GWs for a single-spin precessing phenomenological waveform model (IMRPhenomP) and for an aligned-spin effective-one-body model (SEOBNRv2). The ROQs for SEOBNRv2 use a separate reduced order model (ROM) as a proxy. The ROQs we have constructed are suitable for any power spectrum density function of ground-based GW detector noise. We find speedups in the calculation of inner products and the likelihood function of up to several hundreds, reducing to days analyses which could otherwise take up to a year to complete.

Measurements of black-hole spins in gravitational wave (GW) observations with ground-based detectors are expected to be hampered by partial degeneracies between the two spins, and between the spins and the binary’s mass ratio during the inspiral. If the inspiral and merger-ringdown parts of the GW signal happen to both be in the sensitive frequency band of a GW detector, can we hope to measure both spins and break this degeneracy? Are two-spin models really necessary or are single-spin models sufficient? Using Bayesian parameter estimation we will investigate these questions for a range of configurations over the parameter space for an effective-one-body reduced order model with spins aligned with the orbital angular momentum.

Gravitational waveforms generated by unequal mass black hole binaries are expected to be common sources for future gravitational wave detectors. We derived the waveforms emitted by such systems during the last part of the inspiral, when the larger spin dominates over the orbital angular momentum and the smaller spin is negligible. These Spin-Dominated Waveforms (SDW) arise as a double expansion in the post-Newtonian parameter and another parameter proportional to the ratio of the orbital angular momentum and the dominant spin. The time spent by the gravitational wave as an SDW in the sensitivity range of the KAGRA detector is presented for the first time.