We are working in the description of the main sources of gravitational waves, both for ground- and space-based observatories, with focus on space-based detectors like LISA. The goal of these studies is twofold. First, we want to construct template banks of gravitational waveforms that are fundamental for the data analysis. Second, we need to understand the dynamics of these sources in order to extract the maximum of science from them, that is, the implications of observations of these sources for Astrophysics, Cosmology and Fundamental Physics.
We are also very interested in gravitational physics in general. This includes the structure and properties of black holes, the analysis of different theories of gravity and their consequences, and even analysis of the possible signatures of gravity in high energy physics (for instance, by analyzing ultra-relativistic collisions of black holes).
Last, but not least, we work in the development of different algorithms for Gravitational Wave Data Analysis.
LISA is the mission intended to detect GW, however, due to the challenging technology involved in it, a previous mission in order to assess the technology to be used in LISA has been foreseen. This technological mission is LISA Pathfinder (LPF), and its payload is the LISA Technology Package (LTP).
Our contribution is focused on the design and implementation of the Data and Diagnostics Subsystem (DDS). These elements will monitorise disturbance factors inside the spacecraft providing useful information to characterize the LTP performance. These set of instruments are:
Thermal diagnostic instrumentation: Temperature perturbations are expected to contribute to the LTP noise budget. The temperature diagnostic subsystem will be composed by a set of 24 high stability sensors and 14 precision heaters. Its main purpose is to monitorise the thermal environment and inject controlled heat signal that will characterise the thermal coupling to the experiment. A Front-End Electronics for the temperature subsystem has been designed, manufactured and tested by our group with UPC collaboration.
Magnetic diagnostic instrumentation: The metrology experiment to be performed in the LTP shows a strong dependence in magnetic field and magnetic field gradient perturbations. A set of 4 triaxial magnetometers will measure these magnetic perturbations in-flight. The magnetic diagnostic subsystem is also composed by a set of coils which will induce a controlled magnetic field to fully characterise magnetic induced noise in the experiment. Towards an improved magnetic diagnostic system for LISA, we are currently investigating alternative magnetic sensing based on magnetoresitive sensors with dedicated noise reduction techniques at the sub-milli-Hertz frequency band.
Radiation Monitor: In order to measure the incident flux coming from the Galaxy and from the Sun, a dedicated Radiation Monitor will be characterizing this particle shower in order to study the coupling of this high energy events with the free falling test mass drag-free control loop. Our group together with IFAE has designed and tested the radiation monitor. Test under real high energy proton fluxes and their assessment by means of GEANT4 simulations have shown the instrument is fully ready for flight.
Data Management Unit (DMU): The LTP computer. It is responsible for driving and control of the diagnostics items, and for the acquisition and on-board processing of phasemeter data. It has three electronics components: the Power Distribution Unit (PDU), the Data Acquisition Unit (DAU) and the Data Processing Unit (DPU), each of them duplicated to cover potential failure in flight. DMU Flight Model has undergone extensive testing before its formal acceptance.
The development of this measuring system requires research on new methods of measurement due to the excess noise across the measurement bandwidth. This includes investigation in aspects of sensor technology, analog signal conditioning circuit topologies, low-noise electronic components, analog-to-digital conversion techniques and digital signal processing.
GRLOW: A LOW FREQUENCY TECHNOLOGY TEST-BED
GRLOW is a project funded by the European Commision under a Marie Curie grant to develop a test-bed to test gravitational wave detection related technologies in the very low frequency limit, i.e. below the millihertz.
The project aims to develop a picometer interferometer working in a thermally control chamber in order to suppress environmental perturbations in the very low frequency limit. The technological improvements developed and the results obtained will be of interest for future gravitational wave detectors in space but also for several other space missions which require precise and long-term stability measurements.
Our group participates in the LISA Pathfinder data analysis team. The first objective of the team is to develop a reliable tool to perform data analysis when LISA Pathfinder will be in flight operations. This is the LTPDA toolbox, an objected oriented MATLAB toolbox designed on purpose for the analysis of the LISA Pathfinder data. Our team has contributed to the design of this tool with several data analysis methods that will be used to analyze the data.
Our group is the responsible for the data analysis of the diagnostics on-board the mission. This implies the design, implementation and test of the required tools to deal with this data, that will gather the information coming from 24 thermal sensors, 4 magnetometers and a radiation monitor on board the satellite. Among others, this task requires parameter estimation methods, spectral analysis and digital filter processes.
Our group is also responsible for the design of the diagnostics experiments in-flight. As a part of our commitment, we must define the input signals, integration time, the configuration of the experiment or the required data to be downloaded for each of the experiments that will characterise the environment in the experiment when it will be located in the Lagrange point (L1). Our experiment design description will serve as an input for the Experimental Master Plan, i.e. the sequence of experiments to be performed during operations.
In order to study the system before the launch we use different simulators. To simulate the thermal environment inside the satellite we use ESA’s simulator, ESATAN.
As a part of our contribution to the LTPDA we are developing Monte Carlo Markov Chain (MCMC) algorithms to perform parameter estimation in LISA Pathfinder. MCMC methods are used in different fields due to their robustness in exploring complex parameter spaces. Our group is applying and developing these methods to be used in LISA Pathfinder.