Finding continuous waves from spinning neutron stars and other long-lived sources is a highly challenging data analysis problem. We need to dig extremely weak signals out of large data sets while covering huge unknown parameter spaces. I will review past efforts of the LVK collaboration and wider community and the current state of the field at the start of O4.
"Mountains”, or non-axisymmetric deformations of rotating neutron stars, efficiently radiate gravitational waves. We consider analogies between neutron star mountains and surface features of solar system bodies. Both neutron stars and moons, such as Europa or Enceladus, have thin crusts over deep oceans while Mercury has a thin crust over a large metallic core. Thin sheets may wrinkle in...
With the onset of the era of gravitational-wave astronomy, the search for continuous gravitational
waves, which remain undetected to date, has intensified in more ways than one. Rapidly rotating
neutron stars with non-axisymmetrical deformations of their crusts are the main targets for CGW
searches. The extent of this quadrupolar deformation (commonly referred to as mountains of...
In this talk, I will introduce a simple toy model that can simultaneously explain magnetar glitches and anti-glitches. It is based on the idea of mass ejection from the magnetar and how its magnetic field plays an important part in sustaining the mass quadrupole required for gravitational wave emission. I will use astrophysical arguments to argue that the continuous gravitational waves emitted...
We present the results of the volunteer computing project Einstein@Home all-sky search for continuous gravitational waves in the LIGO O3 public data. This is the most sensitive search to date for the probed waveforms, with frequencies in the 20-800 Hz range and spin-downs between -2.6 x 10^-9 Hz s^-1 and 2.6 x 10^-10 Hz s^-1.
Blind searches for continuous gravitational-wave signals (CWs)
survey broad regions in the parameter-space in order to find
currently unknown sources with possibly no electromagnetic counterpart.
As a result, these searches are amongst the most computationally expensive
searches in the current gravitational-wave data-analysis landscape.
In this work, we revisit the detectability prospects...
One of the key sources for LIGO-Virgo-Kagra is rapidly spinning neutron stars. These long duration and weak signals introduce many computational challenges including analysing large volumes of data and a wide parameter spaces. When searching for continuous signals with no prior knowledge of its frequency evolution, typical matched filtering approaches become computationally infeasible leading...
The GWLab is a virtual laboratory for gravitational wave analysis. The first element of GWLab is a continuous wave search model based on the Viterbi search method. Users can carry out a continuous wave search through an online interface at gwlab.org.au. The aims of this GWLab module are to lower the barrier to entry for continuous wave searches as well as enabling easy data provenance and data...
Spinning neutron stars are sources of long-duration continuous waves (CWs) that may be detected by interferometric detectors. We focus on glitching pulsars with abrupt spin-ups and long term spin-down, which imprint in CWs as transient signals from weeks to months. Standart method for identifying transient signals is the match-filtering, which combines a coherent detection statistics over time...
We focus on long, but not infinite duration continuous wave signals and investigate the statistical properties of the detection statistic in the presence of a transient signal searched with a template grid set up for an always-ON continuous signal. We show how this affects the signal-to-noise ratio in real data in the presence of the noise. Based on this research, we propose a search scheme...
The high computational cost of wide-parameter-space searches for continuous gravitational waves (CWs) significantly limits the achievable sensitivity. This challenge has motivated the exploration of alternative search methods, such as deep neural networks (DNNs). Previous attempts to apply convolutional image-classification DNN architectures to all-sky and directed CW searches showed promise...
Basic mathematical concepts of gravitational-wave data analysis will be introduced. In particular statistical principles of detection of signals in noise and estimation of their parameters are presented. Derivation of the matched-filtering statistic for signal consisting of a linear combination of several functions of unknown parameters will be presented. The case of amplitude and frequency...
Millisecond pulsars are ideal targets to probe the strong interaction at supranuclear densities and search for continuous gravitational wave sources. Either the rotation of their magnetic field or the infall of matter lost by a companion star is assumed to power their electromagnetic emission. Recently, we exploited the fast optical photometer SiFAP2 at 3.6m INAF’s Telescopio Nazionale...
TRAnsients and PUlsars with MeerKAT (TRAPUM) is a large survey project using the new MeerKAT radio interferometer to search for new pulsars in the Southern sky. TRAPUM performs targeted searches of parts of the sky that are most likely to host previously unknown pulsars: globular clusters; nearby galaxies; supernova remnants, pulsar wind nebulae and other TeV sources; and unidentified...
X-ray flux and pulse period fluctuations of accretion-powered pulsars in the Small Magellanic Cloud and elsewhere convey important information about the disk-magnetosphere interaction. In this talk, we present a novel signal processing framework based on the canonical magnetocentrifugal accretion torque and a linear Kalman filter to generate time-dependent estimates of the state variables...
With help from Pulsar timing solutions, it becomes possible to target individual pulsars for their continuous gravitational wave (CW) emission. Such targeted searches are the most sensitive among the various types of CW searches. In the event of a non-detection, the constraints on the gravitational wave strain at twice the spin frequency of the pulsar translate to a constraint on the...
Surveying the sky in search of continuous gravitational waves (CWs) emitted by unknown neutron stars (NSs) is by now a well established practise. The elusiveness of such signals pushes the involved academic community to refine its search techniques and strategies as well as to review the assumptions made on an astrophysical basis.
We discuss both points and study the prospects for detection...
Rotating neutron stars offer great potential as targets for continuous gravitational wave (CW) searches. However their spin frequency may display stochastic fluctuations over time, due to X-ray flux (and hence accretion torque) variability or timing noise. It is crucial to accommodate for this spin-wandering'' in (at least some) CW search algorithms. One approach is to deploy a hidden Markov...
The current and upcoming generations of gravitational wave experiments represent an exciting step forward in terms of detector sensitivity and performance. Key upgrades at the LIGO, Virgo and KAGRA facilities will see the next observing run (O4) probe a spatial volume around four times larger than the previous run (O3), and design implementations for e.g. the Einstein Telescope, Cosmic...
I will present a new concept of a resonant, high frequency GW detector which operates on the basis of optical levitation. This detector will be sensitive to galactic BH superradiance signals, especially those from axions at the GUT scale. I will describe the working principle, the experimental progress, and the projected sensitivity of this detector to continuous GWs.
Detection of continuous waves will open a new frontier in multi-messenger astronomy. I summarize detection prospects for the four main scenarios - pulsar searches, Sco X-1 type directed searches, Cas A type directed searches, and all sky surveys. I include developments in gravitational wave interferometry from now to Einstein Telescope and Cosmic Explorer, and contemporary electromagnetic...
The low-mass X-ray binary Sco X-1 remains the key target for CWG searches, given that it by far outstrips other candidates in terms of expected strain. Efficient searches require the orbit of the NS to be well-constrained. We have been exploiting optical emission lines that trace the binary companion star in the system for over 20 years now. These Bowen fluorescence lines have been an...
The F-statistic is one of the standard methods for CW searches. We will look at its general motivation from both Frequentist and Bayesian perspectives, its frequency-domain implementation in lalpulsar, and the practical aspects of both coherent and semicoherent searches based on it. We will then use the python package PyFstat for some interactive practical examples.
Isolated Neutron Stars (NS) are intriguing sources of continuous gravitational waves (GW) that have yet to be detected. To emit GWs, a star typically requires a mass-energy distribution that deviates from axial symmetry with respect to its rotational axis. This deviation often stems from the non-axisymmetric distribution of magnetic energy, which arises from the coupled magnetic and thermal...
Detection of Gravitational wave events involving neutron stars (NS) provides an excellent scenario for understanding the NS interior. In a binary system, the excitation of NS oscillation modes, such as rotational r-mode and fundamental f-mode, can draw energy from the orbital energy and introduce a phase shift in the observed GW waveform. The ignorance of such dynamical mechanisms can bias the...
The finite size of neutron stars in binary systems has an observable effect on the binary evolution due to tidal interactions. These tidal interactions in circular binaries result in an adiabatic evolution, where the frequency of tidal excitations coevolves with the orbital frequency. However, in case the orbit is eccentric, there is a periodic sharp pulse of external tidal force, which...
