An enhanced sensitivity procedure for continuous gravitational wave detection: targeting the Galactic Center

The recent announcement by the LIGO and Virgo Collaborations of the direct detection of gravitational waves started the era of gravitational wave astrophysics. Each of the GW events detected so far, shed light on multiple aspects of gravity. These last two years of great scientific discoveries would not have been possible without the constant work of generations of scientists all around the world. Commissioning and detector characterization activities required a lot of effort and manpower to reach the sensitivity level and stability needed for the detections. In fact, detector characterization activities continue also during data taking, providing important data quality information to data analysis groups. Although in few years several important results have been obtained, this is just the beginning. Indeed there are several other potential sources of gravitational waves not yet detected. In particular, the search for continuous gravitational waves, which are very weak but long and persistent signals, is a very active field. The most probable sources of continuous waves signals are rapidly rotating asymmetric neutron stars, both isolated or in binary systems. In this thesis I will summarize my 3 years PhD work done in the Rome Virgo group. The main subject is the search for gravitational waves signal emitted by isolated non-axisymmetric rotating neutron stars. After a short introduction to gravitational waves and to the principles of detection (Chapters 1 and 2), in Chapter 3 I will talk about my contribution to detector characterization activities, performed during Virgo commissioning and science runs. I will describe the role played by a spectral lines monitoring tool, called NoEMi (Noise Event Miner), developed by the Rome group in 2010, which I have been responsible for, during these 3 years. NoEMi has been used through O1 and O2 Observational runs and in the commissioning phase of LIGO and Virgo detectors. It has been also used for Virgo data validation of the two gravitational wave events GW170814 and GW170817 and it is currently used for the post-commissioning identification of instrumental lines in both LIGO and Virgo data. The second part of the Thesis is dedicated to the new data analysis framework I have developed in the context of continuous gravitational wave searches. It consists of a novel organization of the data, the so-called Band Sampled Data collection, and of several functions needed to efficiently operate on the data itself. This framework dramatically improves the flexibility in data handling, allowing the user to select and manipulate data in a very efficient way, by properly taking into account the characteristics and the needs of the specific type of search she/he is doing. Overall it results in better computational performance (which, at fixed available computing resources, means better search sensitivity) and immediate adaptability to different kinds of search or, even, to different portions of the same multi-step analysis pipeline. To test the capability of this new framework, a complete pipeline for directed searches of continuous waves signals has been developed using the BSD framework. The pipeline has been applied to a real gravitational wave search (Part III), pointing to the Milky Way central region for which a large number of unknown neutron stars are expected to exist. The results of this search, done using the last observational run (O2) of the LIGO detectors, didn’t show any evidence of the presence of continuous wave emission from the few inner parsecs of our Galaxy. Interesting limits on the minimum detectable strain and ellipticity of the sources have been placed. This is the first directed search for continuous waves signals performed within the Virgo Collaboration and the first LIGO-Virgo O2 directed search toward the Galactic center. The BSD framework developed in this thesis project will become the core of all CW searches of the Rome Virgo group. Furthermore, it represents a great starting point for the development of different types of searches, like that for long transient signals that could be emitted by the post-merger remnant of GW170817

Advanced Virgo: Status of the Detector, Latest Results and Future Prospects

none6noopenBersanetti, Diego; Patricelli, Barbara; Piccinni, Ornella Juliana; Piergiovanni, Francesco; Salemi, Francesco; Sequino, ValeriaBersanetti, Diego; Patricelli, Barbara; Piccinni, Ornella Juliana; Piergiovanni, Francesco; Salemi, Francesco; Sequino, Valeri

First constraints on compact binary environments from LIGO-Virgo data

The LIGO-Virgo analysis of the signals from compact binary mergers observed so far have assumed in-vacuum isolated binary systems, neglecting the potential presence of astrophysical environments. Non-trivial environments may alter gravitational-wave emission, leaving imprints that can be observable via a characteristic dephasing of the emitted signal with respect to the vacuum scenario. We present here the first investigation of environmental effects on the events of the first gravitational-wave catalog (GWTC-1) by LIGO-Virgo. We include the effects of accretion and dynamical friction through a post-Newtonian deformation of the inspiral part of the waveform relative to the vacuum one. We find no evidence for the presence of environmental effects in GWTC-1. Most of the events decisively exclude the scenario of dynamical fragmentation of massive stars as their possible formation channel. Our analysis of GW170817 results in the upper bound on the medium density of $\lesssim 21\: \text{g/cm}^3$. We find that environmental effects can substantially bias the recovered parameters in the vacuum model, even when they are not detectable. Our results forecast that the future 2030s detectors Einstein Telescope and B-DECIGO will be able to probe the environmental effects of accretion disk and superradiant boson clouds on compact binaries.Comment: 13 pages, 7 figures. Comments are welcome

Science with the Einstein Telescope: a comparison of different designs

The Einstein Telescope (ET), the European project for a third-generation gravitational-wave detector, has a reference configuration based on a triangular shape consisting of three nested detectors with 10 km arms, where in each arm there is a `xylophone' configuration made of an interferometer tuned toward high frequencies, and an interferometer tuned toward low frequencies and working at cryogenic temperature. Here, we examine the scientific perspectives under possible variations of this reference design. We perform a detailed evaluation of the science case for a single triangular geometry observatory, and we compare it with the results obtained for a network of two L-shaped detectors (either parallel or misaligned) located in Europe, considering different choices of arm-length for both the triangle and the 2L geometries. We also study how the science output changes in the absence of the low-frequency instrument, both for the triangle and the 2L configurations. We examine a broad class of simple `metrics' that quantify the science output, related to compact binary coalescences, multi-messenger astronomy and stochastic backgrounds, and we then examine the impact of different detector designs on a more specific set of scientific objectives.Comment: 197 pages, 72 figure

Search for gravitational-lensing signatures in the full third observing run of the LIGO-Virgo network

Gravitational lensing by massive objects along the line of sight to the source causes distortions of gravitational wave-signals; such distortions may reveal information about fundamental physics, cosmology and astrophysics. In this work, we have extended the search for lensing signatures to all binary black hole events from the third observing run of the LIGO--Virgo network. We search for repeated signals from strong lensing by 1) performing targeted searches for subthreshold signals, 2) calculating the degree of overlap amongst the intrinsic parameters and sky location of pairs of signals, 3) comparing the similarities of the spectrograms amongst pairs of signals, and 4) performing dual-signal Bayesian analysis that takes into account selection effects and astrophysical knowledge. We also search for distortions to the gravitational waveform caused by 1) frequency-independent phase shifts in strongly lensed images, and 2) frequency-dependent modulation of the amplitude and phase due to point masses. None of these searches yields significant evidence for lensing. Finally, we use the non-detection of gravitational-wave lensing to constrain the lensing rate based on the latest merger-rate estimates and the fraction of dark matter composed of compact objects

Search for eccentric black hole coalescences during the third observing run of LIGO and Virgo

Despite the growing number of confident binary black hole coalescences observed through gravitational waves so far, the astrophysical origin of these binaries remains uncertain. Orbital eccentricity is one of the clearest tracers of binary formation channels. Identifying binary eccentricity, however, remains challenging due to the limited availability of gravitational waveforms that include effects of eccentricity. Here, we present observational results for a waveform-independent search sensitive to eccentric black hole coalescences, covering the third observing run (O3) of the LIGO and Virgo detectors. We identified no new high-significance candidates beyond those that were already identified with searches focusing on quasi-circular binaries. We determine the sensitivity of our search to high-mass (total mass M>70 M⊙) binaries covering eccentricities up to 0.3 at 15 Hz orbital frequency, and use this to compare model predictions to search results. Assuming all detections are indeed quasi-circular, for our fiducial population model, we place an upper limit for the merger rate density of high-mass binaries with eccentricities 0<e≤0.3 at 0.33 Gpc−3 yr−1 at 90\% confidence level

Ultralight vector dark matter search using data from the KAGRA O3GK run

Among the various candidates for dark matter (DM), ultralight vector DM can be probed by laser interferometric gravitational wave detectors through the measurement of oscillating length changes in the arm cavities. In this context, KAGRA has a unique feature due to differing compositions of its mirrors, enhancing the signal of vector DM in the length change in the auxiliary channels. Here we present the result of a search for U(1)B−L gauge boson DM using the KAGRA data from auxiliary length channels during the first joint observation run together with GEO600. By applying our search pipeline, which takes into account the stochastic nature of ultralight DM, upper bounds on the coupling strength between the U(1)B−L gauge boson and ordinary matter are obtained for a range of DM masses. While our constraints are less stringent than those derived from previous experiments, this study demonstrates the applicability of our method to the lower-mass vector DM search, which is made difficult in this measurement by the short observation time compared to the auto-correlation time scale of DM

An enhanced sensitivity procedure for continuous gravitational-wave detection

Isolated rotating neutron stars, asymmetric with respect to their rotational axes, are expected to emit nearly monochromatic gravitational wave signals. The signal arriving at the detector is frequency modulated by the Earth’s motion and by the intrinsic source spin-down. Searches for such signals from stars with parameters only loosely known, or unknown, are computationally challenging because of the large volume of parameter space to be explored. One way to increase the final sensitivity of the search, limiting the high computational cost of it, is presented in this work. We have developed a new framework for future continuous-wave searches, consisting of a fast production of band-limited time series, already downsampled and cleaned. This new setup will be applied to the next all-sky searches for electromagnetically-silent neutron stars and will be used for future searches for signals from Fermi LAT “unassociated” sources, many of which are expected to be neutron stars with completely unknown rotational parameters and a slightly uncertain position

Status and perspectives of Continuous Gravitational Wave searches

The birth of gravitational wave astronomy was triggered by the first detection of a signal produced by the merger of two compact objects (also known as a compact binary coalescence event). The following detections made by the Earth-based network of advanced interferometers had a significant impact in many fields of science: astrophysics, cosmology, nuclear physics and fundamental physics. However, compact binary coalescence signals are not the only type of gravitational waves potentially detectable by LIGO, Virgo, and KAGRA. An interesting family of still undetected signals, and the ones that are considered in this review, are the so-called continuous waves, paradigmatically exemplified by the gravitational radiation emitted by galactic, fast-spinning isolated neutron stars with a certain degree of asymmetry in their mass distribution. In this work, I will review the status and the latest results from the analyses of advanced detector data, including searches for dark matter signatures.Comment: 37 pages, 6 figures, revie