The Laser Interferometer Space Antenna (LISA) will explore the yet-uncharted millihertz band of the gravitational-wave (GW) spectrum in between the very low frequencies probed by pulsar timing arrays and the kilohertz window accessible to ground-based observatories. LISA's adoption is scheduled for early 2024 and data analysis methods are well underway, given the novelty and complexity of the expected data. The GalaxyFIT project aims at designing methods that simultaneously measure and describe the LISA noise, the gravitational-wave signals from thousands of sources, plus gravitational-wave backgrounds from astrophysical and cosmological sources. Integrated methods starting from non-ideal interferometric data all the way to data quality assessments of partially resolved sources are a necessity for LISA to reach its science objectives. GalaxyFIT will focus on ultracompact binary sources in the Milky Way where thousands of sources will be individually resolved and many more will result in an unresolved background, dominating the instrument noise and hampering the detection of a cosmological gravitational wave background. Specifically, GalaxyFIT will establish improved methods for detection and characterization of sources in the presence of non-ideal instrumental noise, and assess the impacts of different data quality cuts on astrophysical inference (measurement of Galactic structure parameters and features in the distributions of the binaries) and the measurement of a cosmological background. GalaxyFIT gathers experts on the LISA instrument, data analysis and astrophysical interpretation and aims to address many of the important data analysis and scientific goals that France has assumed for the LISA Mission, and pave the way for maximised scientific output with the LISA data. GalaxyFIT will also train a new generation of scientists towards this goal.

Einstein's Theory of General Relativity predicts the existence of gravitational waves (GW). A worldwide network of next generation laser interferometers aims at making the first direct detection of GWs from astrophysical sources such as coalescing binaries of neutron-stars and/or black-holes. It will start taking science data by the end of this year (2015). The first discovery of GWs is expected within the decade; this will open an entirely new view of the universe. GW data analysis has reached maturity. Important milestones have been reached during the last science runs. However, a number of important and challenging issues remain open. GW transient detection (our focus here) is very much constrained by important computational requirements. This proposal has the overall objective of improving the analysis of second-generation data and ensure its readiness for the upcoming first GW detection. Coalescing binaries of neutron stars and/or black holes (in short, CBCs, for compact binary coalescences) are considered one of the most promising sources of GWs. The last minutes before the binary merges coincide with the emission of an intense burst of GWs. An accurate modeling of the dynamics of the binary shows that the GW waveform is a quasi-periodic signal with a frequency increasing according to a power law with time, i.e. a chirp. When dealing with multiple detectors, the most sensitive searches analyze the data streams coherently, using sensor array techniques analog to the beam-forming methods used in radio astronomy, for instance. For CBC signals, coherent matched filtering searches are known to be the most sensitive. However, this type of analysis is very computationally demanding and unfeasible in practice. We propose to address this issue with a new search method for such signals based on wavelet graphs. This proposal builds an interdisciplinary team that gathers together mathematicians/statisticians and physicists/data analysis experts that will collaborate to resolve intimately coupled methodological and implementation issues, and to deliver a functional data analysis pipeline ready for production, that will be applied to the scientific data gathered by the gravitational wave interferometers of the latest generation.

The timing of an array of millisecond pulsars (PTA) acts as a galactic-scale detector to observe gravitational wave (GW) sources in the nHz frequency range. The goal of this project is to detect low-frequency GWs while maximizing the scientific output of the Nançay radio telescope (NRT) and participating in operations of the South African MeerKAT radio telescope. We propose new data analysis methods to detect GWs emitted by multiple supermassive black hole binaries in eccentric orbits, while modeling pulsar and noise properties. We will develop a new state-of-the-art pulsar observing backend, to achieve coherent de-dispersion over a very large frequency range (1.5 to 3.5 GHz) and substantially increase our sensitivity at these key radio frequencies. The expected results are the potential first ever detection of GWs in the nHz domain, a much improved understanding of millisecond pulsars and of the weak perturbations that affect their timing stability, and new tests of General Relativity. This project is based on the long-term know-how of a composite team, made of radio astronomers who are specialists in pulsar timing, in Bayesian techniques and in GW data analyses. The NRT already produces high cadence pulsar data with a dedicated state-of-the-art backend enabling us to analyze data from the telescope’s L-band receiver (1.1-1.7 GHz) optimally. The new instrumentation will allow us to cover the whole band accessible with its high frequency S-band receiver, bringing a leap in sensitivity in a domain where the observed radio signal from pulsars is much less affected by interstellar medium perturbations. The support from the ANR will provide us with the resources to fully participate in the scientific exploitation of today’s best radio telescope in the Southern hemisphere, MeerKAT, and allow us to extend the sky coverage for GW searches. This involvement will also firmly install our French team in the long-term preparation of the SKA (Square Kilometer Array) project, which has just been included in the national road map. This is a unique opportunity to train future radio astronomers on one of its key science programs. We will also benefit from our engagement in the LISA project, sharing the expertise accumulated in both communities and building new GW detection algorithms at the interface between both projects, implementing more sophisticated and realistic GW models, and introducing machine learning in the trans-dimensional Bayesian analysis. The PTA technique indeed gives us access to a frequency domain complementary to those covered by Virgo-LIGO and LISA, where one expects GW emission from sources such as super massive black hole binaries (SMBHBs) formed in the long process of galaxy aggregation, and also stochastic GWs from the cosmological background generated by inflation in the very early Universe or by a network of cosmic strings. Characterizing those individual sources (parameters, rate, sky distribution, etc...) would yield unique information about the formation and evolution of SMBHBs through cosmic history and bring original constraints on the hierarchical galaxy formation. Moreover, the detection of this GW signal will allow us to refine the prognoses for SMBHB mergers in the LISA band. To reach these goals, we need a dedicated post-doc involved in both MeerKAT pulsar timing observations and in the combination of data from all radio telescopes involved in the International Pulsar Timing Array organization. Developing and implementing new data analysis techniques at the interface between PTA and LISA is a great project for a PhD student, who will take advantage of the APC environment and get unique skills for the future exploitation of LISA and SKA data. Finally, a strong involvement in MeerKAT and the availability of a wide-band pulsar instrumentation at NRT will clearly maintain the French radio telescope in the race up to the SKA era (>2025) and strengthen our position in the SKA Pulsar Science Working Group.

Observational cosmology is moving towards its next major milestone: high-precision measurements of the cosmic microwave background polarization with the goal of detecting and characterizing the primordial B- modes. These polarization patterns would provide a unique picture of the early Universe, shedding the light on the conditions at that time, be it cosmic inflation, gauge fields, or more exotic possibilities. In a regime of energy where standard models are expected to break, such observations could revolutionize our current picture of cosmology and high energy physics. Characterizing such signal requires (1) reaching extremely low instrumental sensitivity levels and (2) controlling instrumental and astrophysical systematic effects with unprecedented fidelity. While (1) is about to be reached with the planned deployment of funded, cutting-edge observatories such as the Simons Array/ Observatory, CMB-S4 and LiteBIRD, (2) is already limiting the current constraints and will be studied and uniquely mitigated by SCIPOL. My project is an opportunity to claim a leadership role for Europe in one of the most active and impactful research areas in physics, complementing the hardware efforts led by the US and Japan. I will: ‣ construct accurate, open-source and versatile models for the instrumental, astrophysical signals and noise properties; ‣ develop and exploit new, general algorithms adjusting previous models from observations, and producing a unique set of instrument- and foreground-corrected maps; ‣ make a statistically robust cosmological inference of these, especially on the large scale, implementing a gravitational lensing correction. I have been at the forefront of this research for the last 10 years, made key contributions to the analysis and scientific exploitation of the POLARBEAR data sets, and to preparations and scientific optimization of the forthcoming efforts. I am consequently uniquely positioned to deliver the objectives of the proposed work.

As the final product of stellar evolution, neutron stars are exotic bjects both in terms of their internal structure than their electromagnetic activity. We will study the electrodynamics of their magnetosphere using a theoretical and numerical techniques for plasma simulations of highly magnetized relativistic electron/positron pairs bathed in an intense photon field. We will decipher their enigmatic properties by including general relativity effects and of quantum electrodynamics on the dynamics of particles and electromagnetic waves. We will deduce the signatures from it associated observational data in the form of multi-wavelength pulsed radiation from existing and future terrestrial and space telescopes accessible to the various partners of the project.