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This rapidly growing group at CITA focuses on three areas: using numerical relativity to study binary black holes; electromagnetic counterparts to gravitational wave events (such as black hole mergers); and detection and analysis of gravitational waves. In this latter area CITA (jointly with the Perimeter Institute) represents Canada on the LIGO/VIRGO Scientific Collaboration.

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CITA and the Perimeter institute petitioned successfully to join the LIGO/VIRGO Scientific Collaboration. CITA PDF Kipp Cannon serves as Principal Investigator of the CITA/Perimeter group, the first and only Canadian group in this collaboration focused on detection and analysing gravitational waves using ground-based detectors in the US and Europe. This gives CITA access to the detector data for the LIGO gravitational wave detectors. We are enthusiastic about the new opportunities opened by this membership, and by the equally enthusiastic reception of Canada into the LIGO/Virgo Scientific Collaboration. Since joining CITA, Dr. Cannon has continued to analyze data already taken by LIGO, as well as spearheaded development of algorithms for improved data-analysis pipelines that are required for the Advanced LIGO detectors. His work resulted in eight publications during the report period, three of which are publications of the entire collaboration, and five short-authorlist results.

Ilana MacDonald, Samaya Nissanke and Harald Pfeiffer performed an initial analysis of the accuracy requirements for binary black hole gravitational waveforms computed by solving the full Einstein equations. These waveforms are crucial for detecting gravitational waves in the upgraded LIGO detectors currently under construction, and for analyzing any events once they are detected. If the numerical waveforms are not accurate enough, they may compromise the science results of LIGO. Conversely, computing them with higher accuracy than needed wastes computing time that could more usefully spent on simulations at different parameter spaces. The first part of this analysis was published in Classical and Quantum Gravity (also arXiv:1102.5128) with the key result being that the best current numerical simulations are just barely sufficient.

Abdul Mroue and Harald Pfeiffer, with collaborators in the US, UK and Japan, performed the first comparison of periastron advance for comparable mass black hole binaries between fully numerical simulations, and a variety of analytical approximation schemes. Overall, the approximation schemes work as well as one could have reasonably have hoped, with one notable exception: Black hole perturbation theory in mass-ratio (i.e. assuming one black hole has vanishing mass) works astonishingly well even for equal mass binaries if one makes a certain simply substitution in the formulae. This work is in print at Physical Review Letters (also arXiv:1106.3278).

Abdul Mroue and Harald Pfeiffer, with collaborators at Cornell and Maryland, developed techniques which allow control over the orbital eccentricity in numerical simulations of inspiraling binary black holes. This allows the numerical simulations to now target easily the most relevant portion of parameter space, namely zero eccentricity. These new results extend this capability to generic spinning, precessing binary black holes (published in Physical Review D; also arXiv:1012.1549).

Carlos Palenzuela, together with other collaborators, studied possible electromagnetic counterparts to loud gravitational wave events. In particular, they studied the merger of supermassive black holes immersed on the external magnetic fields sourced by a circumbinary disk, a likely last stage of the collision of galaxies. It is shown that the EM fields can extract not only rotational energy from the black holes through the well-known Blandford-Znajek effect, but also translational kinetic energy in the form of a dual jet, carrying enough energy to be observable at large distances. The robustness of the standard Blandford-Znajek effect was studied in a different work.