A5061169663- Pulsars and Gravitational Waves Research
- Gamma-ray bursts and supernovae
- Geophysics and Gravity Measurements
- High-pressure geophysics and materials
- Astrophysical Phenomena and Observations
- Cosmology and Gravitation Theories
- earthquake and tectonic studies
- Astrophysics and Cosmic Phenomena
- Atomic and Subatomic Physics Research
- Solar and Space Plasma Dynamics
- Radio Astronomy Observations and Technology
- Statistical Mechanics and Entropy
- Dark Matter and Cosmic Phenomena
- Geophysics and Sensor Technology
- Inertial Sensor and Navigation
- Cold Atom Physics and Bose-Einstein Condensates
- Earthquake Detection and Analysis
- Seismology and Earthquake Studies
- Monetary Policy and Economic Impact
- Black Holes and Theoretical Physics
- Geomagnetism and Paleomagnetism Studies
- Magnetic confinement fusion research
- Economics of Agriculture and Food Markets
- Complex Systems and Time Series Analysis
- Astronomical Observations and Instrumentation
The University of Melbourne
1989-2025
ARC Centre of Excellence for Gravitational Wave Discovery
2020-2025
Australian Research Council
2020-2025
The characterization of the Advanced LIGO detectors in second and third observing runs has increased sensitivity instruments, allowing for a higher number detectable gravitational-wave signals, provided confirmation all observed events. In this work, we present methods used to characterize curate publicly available datasets, including strain data quality products. We describe essential role these datasets LIGO-Virgo Collaboration analyses gravitational-waves from both transient persistent...
Abstract Gravitational waves from coalescing neutron stars encode information about nuclear matter at extreme densities, inaccessible by laboratory experiments. The late inspiral is influenced the presence of tides, which depend on star equation state. Neutron mergers are expected to often produce rapidly rotating remnant that emit gravitational waves. These will provide clues extremely hot post-merger environment. This signature in contains most 2–4 kHz frequency band, outside sensitive...
Abstract Stochastic fluctuations in the spin frequency ν of a rotation-powered pulsar affect how accurately one measures power-law braking index, npl, defined through $\dot{\nu }=K\nu ^{n_{\rm pl}}$, and can lead to measurements anomalous indices, with $\vert n \vert = \nu \ddot{\nu }/ \dot{\nu }^{2} \gg 1$, where overdot symbolizes derivative respect time. Previous studies show that variance measured obeys predictive, falsifiable formula $\langle n^{2} \rangle n_{\rm pl}^{2}+\sigma...
We present results of a follow-up search for continuous gravitational waves (CWs) associated with subthreshold candidates from the LIGO-Virgo-KAGRA (LVK) all-sky all-frequency (ASAF) directed radiometer analysis, using Advanced LIGO data third observing run (O3). Each ASAF candidate corresponds to $1/32\text{ }\text{ }\mathrm{Hz}$ frequency band and $\ensuremath{\sim}13\text{ }{\mathrm{deg}}^{2}$ sky pixel. Assuming they represent possible CW sources, we analyze all 515 semi-coherent,...
Abstract The stochastic gravitational wave background (SGWB) can be observed in the nanohertz band using a pulsar timing array (PTA). Here computationally efficient state-space framework is developed for analysing SGWB data, which strain at Earth tracked with non-linear Kalman filter and separated simultaneously from intrinsic, achromatic spin wandering. combined nested sampler to estimate parameters of model, calculate Bayes factor selecting between models without SGWB. procedure extends...
Radio pulsar glitches probe far-from-equilibrium processes involving stress accumulation and relaxation in neutron star interiors. Previous studies of glitch rates have focused on individual pulsars with as many recorded possible. In this work we analyze using all available data including objects that glitched never or once. We assume the rate follows a homogeneous Poisson process, therefore exclude which exhibit quasiperiodic glitching behavior. Calculating relevant Bayes factors shows...
Glitching pulsars fall broadly into two statistical classes: those with Poisson-like waiting times and power-law sizes, unimodal sizes. Previous glitch modelling based on a state-dependent Poisson process readily generates behaviour but struggles to produce or Here it is shown that, when some of the inputs model are modified, both classes can be reproduced by varying single control parameter related spin-down rate. The implications for past future observations underlying microphysical...
Following up large numbers of candidates in continuous gravitational-wave searches presents a challenge, particularly regard to computational power and the time required manually scrutinize each candidates. It is important design test good follow-up procedures that are safe (i.e., minimize false dismissals) computationally efficient across many search configurations. We investigate two procedures, or ``vetoes,'' both which exploit Doppler modulation predicted astrophysical signals. In...
Among the five pulsars with most recorded rotational glitches, only PSR J0534$+$2200 is found to have an autocorrelation between consecutive glitch sizes which differs significantly from zero (Spearman correlation coefficient $\rho=-0.46$, p-value $=0.046$). No statistically compelling autocorrelations waiting times are found. The observations interpreted within framework of a predictive meta-model describing stress-release in terms state-dependent Poisson process. Specific combinations size...
A microphysics-agnostic meta-model of rotational glitches in rotation-powered pulsars is developed, wherein the globally averaged internal stress accumulates as a Brownian process between glitches, and glitch triggered once critical threshold surmounted. Precise, falsifiable predictions are made regarding long-term event statistics individual pulsars. For example, Spearman cross-correlation coefficient size waiting time until next should exceed 0.25 all Among six with most recorded PSR...
ABSTRACT Superfluid vortices pinned to nuclear lattice sites or magnetic flux tubes in a neutron star evolve abruptly through sequence of metastable spatial configurations, punctuated by unpinning avalanches associated with rotational glitches, as the stellar crust spins down electromagnetically. The configurations are approximately but not exactly axisymmetric, causing emission persistent, quasimonochromatic, current quadrupole gravitational radiation. characteristic wave strain h0 function...
Continuous nanohertz gravitational waves from individual supermassive black hole binaries may be detectable with pulsar timing arrays. A novel search strategy is developed, wherein intrinsic achromatic spin wandering tracked simultaneously the modulation induced by a single wave source in pulse times of arrival. two-step inference procedure applied within state-space framework, such that Kalman filter, which then provides likelihood for nested sampling. The estimates static parameters...
It is an open question whether glitch activity in individual pulsars varies on decadal time-scales. The Crab pulsar has experienced 23 spin-up glitches the last 36 years, interrupting otherwise monotonic deceleration. A homogeneous Poisson process, i.e. a process with constant rate, not sufficient to describe time-ordered distribution of epochs pulsar. There are signs clustering at $2\sigma$ level when testing Ripley's $K$ function. Two alternative, inhomogeneous models one and two step-wise...
Abstract Stress accumulation-relaxation meta-models of pulsar glitches make precise, microphysics-agnostic predictions long-term glitch statistics, which can be falsified by existing and future timing data. Previous assume that are triggered an avalanche process, e.g., involving superfluid vortices, the probability density function (PDF) sizes is history independent specified exogenously. Here, a recipe proposed to generate endogenously in history-dependent manner, tracking thresholds...
Abstract Three detailed case studies illustrating the seasonal analysis of economic time series are presented using component models for and nonseasonal behavior. Analyses performed within a semi-Bayesian framework where inferences target quantities interest, such as seasonally adjusted values, obtained posterior distributions conditional on observed data fitted parameter values. Such an approach is similar to previous model-based methods analysis, but new algorithms used and, more...
Solar flares result from the sudden release of energy deposited by sub-photospheric motions into magnetic field corona. The accumulates secularly between events. One may interpret observed event statistics as resulting a state-dependent Poisson process, in which instantaneous flare rate is function stress system, and becomes certain approaches threshold set micro-physics trigger. If system driven fast, if static uniform globally, cross-correlation predicted size forward waiting time to next...
Superfluid vortices pinned to nuclear lattice sites or magnetic flux tubes in a neutron star evolve abruptly through sequence of metastable spatial configurations, punctuated by unpinning avalanches associated with rotational glitches, as the stellar crust spins down electromagnetically. The configurations are approximately but not exactly axisymmetric, causing emission persistent, quasimonochromatic, current quadrupole gravitational radiation. characteristic wave strain $h_0$ function spin...
ABSTRACT Continuous nanohertz gravitational waves from individual supermassive black hole binaries may be detectable with pulsar timing arrays. A novel search strategy is developed, wherein intrinsic achromatic spin wandering tracked simultaneously the modulation induced by a single wave source in pulse times of arrival. two-step inference procedure applied within state-space framework, such that Kalman filter, which then provides likelihood for nested sampling. The estimates static...
ABSTRACT Pulsar timing arrays (PTA) can detect continuous nanohertz gravitational waves (GW) emitted by individual supermassive black hole binaries. The data analysis procedure be formulated within a time-domain, state-space framework, in which the radio observations are related to temporal sequence of latent states, namely intrinsic pulsar spin frequency. achromatic wandering frequency is tracked using Kalman filter concurrently with pulse modulation induced GW from single source. sum terms...
Pulsar timing arrays can detect continuous nanohertz gravitational waves emitted by individual supermassive black hole binaries. The data analysis procedure be formulated within a time-domain, state-space framework, in which the radio observations are related to temporal sequence of latent states, namely intrinsic pulsar spin frequency. achromatic wandering frequency is tracked using Kalman filter concurrently with pulse modulation induced wave from single source. sum terms proportional...
Solar flares result from the sudden release of energy deposited by sub-photospheric motions into magnetic field corona. The accumulates secularly between events. One may interpret observed event statistics as resulting a state-dependent Poisson process, in which instantaneous flare rate is function stress system, and becomes certain approaches threshold set micro-physics trigger. If system driven fast, if static uniform globally, cross-correlation predicted size forward waiting time to next...
We present results of a follow-up search for continuous gravitational waves (CWs) associated with sub-threshold candidates from the LIGO-Virgo-KAGRA (LVK) All-Sky All-Frequency (ASAF) directed radiometer analysis, using Advanced LIGO data third observing run (O3). Each ASAF candidate corresponds to $1/32\,\,\mathrm{Hz}$ frequency band and ${\sim}13\,\,\mathrm{deg}^2$ sky pixel. Assuming they represent possible CW sources, we analyze all $515$ semi-coherent, $\mathcal{F}$-statistic-based...
Following up large numbers of candidates in continuous gravitational wave searches presents a challenge, particularly regard to computational power and the time required manually scrutinize each candidates. It is important design test good follow-up procedures that are safe (i.e., minimize false dismissals) computationally efficient across many search configurations. We investigate two procedures, or "vetoes," both which exploit Doppler modulation predicted astrophysical signals. In...