arXiv subjects

Martina Muratore

Publications and source records attributed to Martina Muratore.

13 recordsLinked to original sources

arXiv2025

A flexible, GPU-accelerated approach for the joint characterization of LISA instrumental noise and Stochastic Gravitational Wave Backgrounds

LISA data analysis represents one of the most challenging tasks ahead for the future of gravitational-wave (GW) astronomy. Characterizing the instrument's noise properties while fitting for all the other detectable sources is a key requirement of any robust inference pipeline. Noise estimation will also play a crucial role in searches and parameter estimation of cosmological and astrophysical stochastic signals. Previous studies have tackled this topic by assuming perfect knowledge of the spectral shape of the instrumental noise and of different possible types of GW Stochastic Backgrounds (SGWBs), usually resorting to parametrized templates. Recently, various works that employ template-agnostic methods have been presented. In this work, we take an additional step further, introducing flexible spectral shapes in both the instrumental noise and the stochastic signals. We account for the lack of knowledge of the exact shape of the individual contributions to the overall power spectral density by using splines to represent arbitrary perturbations of the noise and signal spectral densities. We implement a data-driven Reversible Jump MCMC algorithm to fit different components simultaneously and to infer the level of flexibility required under different scenarios. We test this approach on simulated LISA data produced under different assumptions. We investigate the impact of this increased flexibility on the reconstruction of both the injected signal and the noise level, and we discuss the prospects for claiming a successful SGWB detection.

gr-qc↗

arXiv2025

The impact of missing data on the construction of LISA Time Delay Interferometry Michelson variables

We investigate the impact of missing input data on the construction of second-generation Time Delay Interferometry (TDI) variables, which enable data analysis for the Laser Interferometer Space Antenna (LISA). TDI relies on the introduction of precise time delays into the raw interferometric data streams before they are combined to suppress otherwise dominant laser phase noise. We show that a single missing sample, corresponding to 0.25 s of data, will result in an effective data gap of approximately 90 s in the second-generation TDI output if further measures are not taken. This additional gap is largely independent of the initial gap duration, but increases linearly with the order of the fractional-delay filter used for the computations. For a realistic gap scenario, incorporating both planned and unplanned data interruptions consistent with a target duty cycle of ~84%, we find that frequent, short-duration gaps (e.g., a total of 1000 per year, each of which have short durations ~ 100 s) could result in an additional loss in the TDI variables of about one day per year corresponding to a ~0.3% reduction in duty cycle. This amounts to a loss of approximately one day of LISA data suitable for the global-fit per year.

gr-qc↗

arXiv2025

A pipeline for searching and fitting instrumental glitches in LISA data

Instrumental artefacts, such as glitches, can significantly compromise the scientific output of LISA. Our methodology employs advanced Bayesian techniques, including Reversible Jump Markov Chain Monte Carlo and parallel tempering to find and characterize glitches and astrophysical signals. The robustness of the pipeline is demonstrated through its ability to simultaneously handle diverse glitch morphologies and it is validated with a 'Spritz'-type data set from the LISA Data Challenge. Our approach enables accurate inference on Massive Black Hole Binaries, while simultaneously characterizing both instrumental artefacts and noise. These results present a significant development in strategies for differentiating between instrumental noise and astrophysical signals, which will ultimately improve the accuracy and reliability of source population analyses with LISA.

gr-qc↗

arXiv2025

Searching for continuous gravitational waves from slowly spinning neutron stars with DECIGO, Big Bang Observer, Einstein Telescope and Cosmic Explorer

We consider stably rotating highly magnetised neutron stars and glitching pulsars. We discuss the prospects for detecting continuous gravitational waves from these sources below 20 Hz with next-generation ground-based facilities such as the Einstein Telescope and Cosmic Explorer and space-based observatories such as DECIGO and Big Bang Observer. We demonstrate that these constitute interesting science targets. We use a robust sensitivity estimation method for future searches based on demonstrated performance. We show that the spin-down upper limit on the gravitational wave amplitude of all highly magnetised pulsars and magnetars suitable for a years-long fully coherent search, exceeds the smallest gravitational wave amplitude estimated detectable with DECIGO and Big Bang Observer. We find that the hidden magnetar candidate PSR J1852+0040 can be detected by Cosmic Explorer if it is emitting at least at 20% of its spin-down luminosity. Finally, post-glitch transient continuous gravitational waves from magnetars are an interesting target for deci-Hz detectors, with all but one of the recorded glitches giving rise to a spin-down limit signal above the smallest detectable level.

astro-ph.HE↗

arXiv2024

LISA test-mass charging. Particle flux modeling, Monte Carlo simulations and induced effects on the sensitivity of the observatory

Context. The LISA space observatory will explore the sub-Hz spectrum of gravitational wave emission from the Universe. The space environment, where will be immersed in, is responsible for charge accumulation on its free falling test masses (TMs) due to the galactic cosmic rays (GCRs) and solar energetic particles (SEP) impinging on the spacecraft. Primary and secondary particles produced in the spacecraft material eventually reach the TMs by depositing a net positive charge fluctuating in time. This work is relevant for any present and future space missions that, like LISA, host free-falling TMs as inertial reference. Aims. The coupling of the TM charge with native stray electrostatic field produces noise forces on the TMs, which can limit the performance of the LISA mission. A precise knowledge of the charging process allows us to predict the intensity of these charge-induced disturbances and to design specific counter-measures. Methods. We present a comprehensive toolkit that allows us to calculate the TM charging time-series in a geometry representative of LISA mission, and the associated induced forces under different conditions of the space environment by considering the effects of short, long GCR flux modulations and SEPs. Results. We study, for each of the previously mentioned conditions, the impact of spurious forces associated with the TM charging process on the mission sensitivity for gravitational wave detection.

astro-ph.IM↗

arXiv2024

LISA Definition Study Report

The Laser Interferometer Space Antenna (LISA) is the first scientific endeavour to detect and study gravitational waves from space. LISA will survey the sky for Gravitational Waves in the 0.1 mHz to 1 Hz frequency band which will enable the study of a vast number of objects ranging from Galactic binaries and stellar mass black holes in the Milky Way, to distant massive black-hole mergers and the expansion of the Universe. This definition study report, or Red Book, presents a summary of the very large body of work that has been undertaken on the LISA mission over the LISA definition phase.

astro-ph.CO↗

arXiv2023

Impact of the noise knowledge uncertainty for the science exploitation of cosmological and astrophysical stochastic gravitational wave background with LISA

This paper investigates the impact of a lack of knowledge of the instrumental noise on the characterisation of stochastic gravitational wave backgrounds with the Laser Interferometer Space Antenna (LISA). We focus on constraints on modelled backgrounds that represent the possible backgrounds from the mergers of binary black holes of stellar origin, from primordial black hole generation, from non-standard inflation, and from sound wave production during cosmic fluid phase transitions. We use splines to model generic, slowly varying, uncertainties in the auto and cross-spectral densities of the LISA time delay interferometry channels. We find that allowing for noise knowledge uncertainty in this way leads to one to two orders of magnitude degradation in our ability to constrain stochastic backgrounds, and a corresponding increase in the background energy density required for a confident detection. We also find that to avoid this degradation, the LISA noise would have to be known at the sub-percent level, which is unlikely to be achievable in practice.

gr-qc↗

arXiv2023

Stochastic gravitational wave background reconstruction for a non-equilateral and unequal-noise LISA constellation

We explore the impact of choosing different sets of Time-Delay Interferometry (TDI) variables for detecting and reconstructing Stochastic Gravitational Wave Background (SGWB) signals and estimating the instrumental noise in LISA. Most works in the literature build their data analysis pipelines relying on a particular set of TDI channels, the so-called AET variables, which are orthogonal under idealized conditions. By relaxing the assumption of a perfectly equilateral LISA configuration, we investigate to which degree these channels remain orthogonal and compare them to other TDI channels. We show that different sets of TDI variables are more robust under perturbations of the perfect equilateral configuration, better preserving their orthogonality and, thus, leading to a more accurate estimate of the instrumental noise. Moreover, we investigate the impact of considering the noise levels associated with each instrumental noise source to be independent of one another, generalizing the analysis from two to twelve noise parameters. We find that, in this scenario, the assumption of orthogonality is broken for all the TDI variables, leading to a misestimation of measurement error for some of the noise parameters. Remarkably, we find that for a flat power-law signal, the reconstruction of the signal parameters is nearly unaffected in these various configurations.

gr-qc↗

arXiv2023

On the effectiveness of null TDI channels as instrument noise monitors in LISA

We present a study of the use and limits of the Time-Delay Interferometry null channels for in flight estimation of the Laser Interferometer Space Antenna instrumental noise. The paper considers how the two main limiting noise sources, test-mass acceleration noise and interferometric phase measurement noise, propagate through different Time-Delay Interferometry channels: the Michelson combination X that is the most sensitive to gravitational waves, then the less-sensitive combinations $α$, and finally the null channel $ζ$. We note that the null channel $ζ$, which is known to be equivalent to any null channel, not only has a reduced sensitivity to the gravitational waves, but also feature a larger degree of cancellation of the test mass acceleration noise relative to the interferometry noise. This severely limits its use in quantifying the low frequency instrumental noise in the Michelson X combination, which is expected to be dominated by acceleration noise. However, we show that one can still use in-flight noise estimations from $ζ$ to put an upper bound on the considered noises entering in the X channel, which allows to distinguish them from a strong stochastic gravitational wave background.

gr-qc↗

arXiv2022

Characterization of Time Delay Interferometry combinations for the LISA instrument noise

Time delay interferometry (TDI) is a post-processing technique used in the Laser Interferometer Space Antenna (LISA) to reduce laser frequency noise by building an equal-arm interferometer via combining time-shifted raw phase measurements. The set of so-called 2nd generation TDI variables which sufficiently suppress laser frequency noise considering realistic LISA orbital dynamics has recently been expanded by a large number of additional solutions. In this paper, we characterize these new TDI channels by relating them to the well-known 1st generation variables $α$, $β$, $γ$, and $ζ$. We compute explicitly how each 2nd generation variable can be approximated as a linear combination of these four 1st generation variables, and show numerically that these approximations are accurate enough to model the noises not suppressed by TDI. We use these results to discuss how the newly found channels might be advantageous to use for the LISA data analysis. In addition, we demonstrate that newly found variants of the variable $ζ$ significantly out-perform the ones previously known from the literature.

gr-qc↗

arXiv2022

Time Delay Interferometry combinations as instrument noise monitors for LISA

The LISA mission will likely be a signal dominated detector, such that one challenge is the separation of the different astrophysical sources, and to distinguish between them and the instrumental noise. One of the goals of LISA is to probe the early Universe by detecting stochastic GW backgrounds. As correlation with other detectors is not possible for LISA, discrimination of such a GW background from the instrumental noise requires a good estimate of the latter. To this purpose we have revisited Time Delay Interferometry (TDI) to look for new TDI signal combinations that fulfill the laser frequency noise suppression requirements. We illustrate that it is possible to do a linear combination of these TDI channels to find special null-combinations that suppress gravitational waves and mainly carry information about instrumental noise. We find that there exist many null-combinations that show different sensitivities to gravitational waves, some of which seem more suitable than the traditional T combination for estimating test-mass acceleration noise. In an idealised LISA configuration, they are all sensitive to a particular linear combination of the six test-masses acceleration, similar to a rigid rotation of the LISA triangle. In the following article, we illustrate what are the noise properties that can be extracted by monitoring these interferometry signals and discuss the implication of these findings for the detection of stochastic GW backgrounds.

gr-qc↗

arXiv2021

Legacy of the First Workshop on Gravitational Wave Astrophysics for Early Career Scientists

Gravitational wave science is a dynamical, fast-expanding research field founded on results, tools and methodologies drawn from different research areas and communities. Early career scientists entering this field must learn and combine knowledge and techniques from a range of disciplines. The Workshop on Gravitational-Wave Astrophysics for Early Career Scientists (GWAECS), held virtually in May 2021, planted the seeds of an interdisciplinary, well-connected and all-inclusive community of early career scientists working on gravitational waves, able to exchange relevant information and ideas, build a healthy professional and international environment, share and learn valuable skills, and ensure that ongoing research efforts are perpetuated and expanded in order to attain the main scientific goals envisioned by the whole community. GWAECS was the first event unifying early career scientists belonging to different communities, historically associated with different large-scale gravitational wave experiments. It provided a broad perspective on the future of gravitational waves, offered training on soft and transferable skills and allowed ample time for informal discussions between early career scientists and well-known research experts. The essence of those activities is summarised and collected in the present document, which presents a recap of each session of the workshop and aims to provide all early career scientists with a long-lasting, useful reference which constitutes the legacy of all the ideas that circulated at GWAECS.

gr-qc↗

arXiv2020

Revisitation of time delay interferometry combinations that suppress laser noise in LISA

With the purpose of understanding how time delay interferometry (TDI) combinations can best be used for the characterisation of LISA instrumental noise, we revisit their laser frequency noise cancellation properties. We have developed an algorithm to search for all possible combinations that suppress noise at the same level as the X, Y and Z classical combination. The algorithm calculates delays using symbolic formulas that explicitly include velocities and accelerations of satellites up to the relevant order. In addition, once a combination has been identified, delays are verified by solving numerically the relevant equations using Keplerian orbits and Shapiro delay corrections. We find that the number of combinations that suppress the noise is larger than what was reported in the literature. In particular we find that some combinations that were thought to only partly suppress the noise, in reality do suppress it at the same level of accuracy as the basic X, Y and Z combinations.

astro-ph.IM↗