arXiv subjects

M. Pitkin

Publications and source records attributed to M. Pitkin.

16 recordsLinked to original sources

arXiv2026

The G347.3-0.5 outlier from O3: a follow-up case study for continuous gravitational-wave candidates

We report a multi-pipeline follow-up study of the continuous gravitational-wave (CW) outlier identified by the Ming et al. Einstein@Home directed search for the young supernova remnant G347.3-0.5 (containing the central compact object RXJ1713.7-3946). The outlier was initially identified in LIGO data from the O3a observing run and followed up with the addition of O3b and O4a data by the Einstein@Home pipeline, with O4a producing weaker evidence. Here, we show extended data quality checks and results from three pipelines that have independently investigated this outlier, including the newly released O4b data set. We can robustly recover the outlier in O3, while we find no evidence for a related standard CW signal in O4a (consistent with Ming et al.) and O4b data. This work serves as a useful test case for future multi-pipeline follow-ups of CW candidates that aim to investigate their astrophysical or noise nature, and it is therefore an important step in preparation for the first CW detection.

gr-qc↗

arXiv2024

Recovering Pulsar Braking Index from a Population of Millisecond Pulsars

The braking index, $n$, of a pulsar is a measure of its angular momentum loss and the value it takes corresponds to different spin-down mechanisms. For a pulsar spinning down due to gravitational wave emission from the principal mass quadrupole mode alone, the braking index would equal exactly 5. Unfortunately, for millisecond pulsars, it can be hard to measure observationally due to the extremely small second time derivative of the rotation frequency, $\ddot{f}$. This paper aims to examine whether it could be possible to extract the distribution of $n$ for a whole population of pulsars rather than measuring the values individually. We use simulated data with an injected $n=5$ signal for 47 millisecond pulsars and extract the distribution using hierarchical Bayesian inference methods. We find that while possible, observation times of over 20 years and RMS noise of the order of $10^{-5}$ ms are needed, which can be compared to the mean noise value of $3\times10^{-4}$ ms for the recent wideband 12.5-year NANOGrav sample, which provided the pulsar timing data used in this paper.

astro-ph.HE↗

arXiv2020

Bayesian inference for compact binary coalescences with BILBY: Validation and application to the first LIGO--Virgo gravitational-wave transient catalogue

Gravitational waves provide a unique tool for observational astronomy. While the first LIGO--Virgo catalogue of gravitational-wave transients (GWTC-1) contains eleven signals from black hole and neutron star binaries, the number of observations is increasing rapidly as detector sensitivity improves. To extract information from the observed signals, it is imperative to have fast, flexible, and scalable inference techniques. In a previous paper, we introduced BILBY: a modular and user-friendly Bayesian inference library adapted to address the needs of gravitational-wave inference. In this work, we demonstrate that BILBY produces reliable results for simulated gravitational-wave signals from compact binary mergers, and verify that it accurately reproduces results reported for the eleven GWTC-1 signals. Additionally, we provide configuration and output files for all analyses to allow for easy reproduction, modification, and future use. This work establishes that BILBY is primed and ready to analyse the rapidly growing population of compact binary coalescence gravitational-wave signals.

astro-ph.IM↗

arXiv2018

Hierarchical Bayesian method for detecting continuous gravitational waves from an ensemble of pulsars

When looking for gravitational wave signals from known pulsars, targets have been treated using independent searches. Here we use a hierarchical Bayesian framework to combine observations from individual sources for two purposes: to produce a detection statistic for the whole ensemble of sources within a search, and to estimate the hyperparameters of the underlying distribution of pulsar ellipticities. Both purposes require us to assume some functional form of the ellipticity distribution, and as a proof of principle we take two toy distributions. One is an exponential distribution, defined by its mean, and the other is a half-Gaussian distribution defined by its width. We show that by incorporating a common parameterized prior ellipticity distribution we can be more efficient at detecting gravitational waves from the whole ensemble of sources than trying to combine observations with a simpler non-hierarchical method. This may allow us to detect gravitational waves from the ensemble before there is confident detection of any single source. We also apply this method using data for 92 pulsars from LIGO's sixth science run. No evidence for a signal was seen, but 90\% upper limits of $3.9\ee{-8}$ and $4.7\ee{-8}$ were set on the mean of an assumed exponential ellipticity distribution and the width of an assumed half-Gaussian ellipticity distribution, respectively.

astro-ph.IM↗

arXiv2018

Reduced order modelling in searches for continuous gravitational waves - I. Barycentering time delays

The frequencies and phases of emission from extra-solar sources measured by Earth-bound observers are modulated by the motions of the observer with respect to the source, and through relativistic effects. These modulations depend critically on the source's sky-location. Precise knowledge of the modulations are required to coherently track the source's phase over long observations, for example, in pulsar timing, or searches for continuous gravitational waves. The modulations can be modelled as sky-location and time-dependent time delays that convert arrival times at the observer to the inertial frame of the source, which can often be the Solar system barycentre. We study the use of reduced order modelling for speeding up the calculation of this time delay for any sky-location. We find that the time delay model can be decomposed into just four basis vectors, and with these the delay for any sky-location can be reconstructed to sub-nanosecond accuracy. When compared to standard routines for time delay calculation in gravitational wave searches, using the reduced basis can lead to speed-ups of 30 times. We have also studied components of time delays for sources in binary systems. Assuming eccentricities $< 0.25$ we can reconstruct the delays to within 100s of nanoseconds, with best case speed-ups of a factor of 10, or factors of two when interpolating the basis for different orbital periods or time stamps. In long-duration phase-coherent searches for sources with sky-position uncertainties, or binary parameter uncertainties, these speed-ups could allow enhancements in their scopes without large additional computational burdens.

astro-ph.HE↗

arXiv2016

Validating gravitational-wave detections: The Advanced LIGO hardware injection system

Hardware injections are simulated gravitational-wave signals added to the Laser Interferometer Gravitational-wave Observatory (LIGO). The detectors' test masses are physically displaced by an actuator in order to simulate the effects of a gravitational wave. The simulated signal initiates a control-system response which mimics that of a true gravitational wave. This provides an end-to-end test of LIGO's ability to observe gravitational waves. The gravitational-wave analyses used to detect and characterize signals are exercised with hardware injections. By looking for discrepancies between the injected and recovered signals, we are able to characterize the performance of analyses and the coupling of instrumental subsystems to the detectors' output channels. This paper describes the hardware injection system and the recovery of injected signals representing binary black hole mergers, a stochastic gravitational wave background, spinning neutron stars, and sine-Gaussians.

astro-ph.IM↗

arXiv2016

Astrophysical calibration of gravitational-wave detectors

We investigate a method to assess the validity of gravitational-wave detector calibration through the use of gamma-ray bursts as standard sirens. Such signals, as measured via gravitational-wave observations, provide an estimated luminosity distance that is subject to uncertainties in the calibration of the data. If a host galaxy is identified for a given source then its redshift can be combined with current knowledge of the cosmological parameters yielding the true luminosity distance. This will then allow a direct comparison with the estimated value and can validate the accuracy of the original calibration. We use simulations of individual detectable gravitational-wave signals from binary neutron star (BNS) or neutron star-black hole systems, which we assume to be found in coincidence with short gamma-ray bursts, to estimate any discrepancy in the overall scaling of the calibration for detectors in the Advanced LIGO and Advanced Virgo network. We find that the amplitude scaling of the calibration for the LIGO instruments could on average be confirmed to within $\sim 10\%$ for a BNS source within 100 Mpc. This result is largely independent of the current detector calibration method and gives an uncertainty that is competitive with that expected in the current calibration procedure. Confirmation of the calibration accuracy to within $\sim 20\%$ can be found with BNS sources out to $\sim 500$ Mpc.

astro-ph.IM↗

arXiv2015

First results and future prospects for dual-harmonic searches for gravitational waves from spinning neutron stars

We investigate a method to incorporate signal models that allow an additional frequency harmonic in searches for gravitational waves from spinning neutron stars. We assume emission is given by the general triaxial non-aligned model of Jones, whose waveform under certain conditions reduces to that of a biaxial precessing star, or a simple rigidly rotating triaxial aligned star. The triaxial non-aligned and biaxial models can produce emission at both the star's rotation frequency ($f$) and $2f$, whilst the latter only emits at $2f$. We have studied parameter estimation for signal models using both a set of physical source parameters, and a set of waveform parameters that remove a degeneracy. We have assessed the signal detection efficiency, and used Bayesian model selection to investigate how well we can distinguish between the three models. We found that for signal-to-noise ratios (SNRs) $\gtrsim 6$ there is no significant loss in efficiency if performing a search for a signal at $f$ and $2f$ when the source is only producing emission at $2f$. However, for sources with emission at both $f$ and $2f$ signals could be missed by a search only at $2f$. We also find that for a triaxial aligned source, the correct model is always favoured, but for a triaxial non-aligned source it can be hard to distinguish between the triaxial non-aligned model and the biaxial model, even at high SNR. Finally, we apply the method to a selection of known pulsars using data from the LIGO fifth science run. We give the first upper limits on gravitational wave amplitude at both $f$ and $2f$ and apply the model selection criteria on real data.

astro-ph.HE↗

arXiv2015

Comment on "Measurements of Newton's gravitational constant and the length of day"

There have been recent claims (Anderson et al., EPL, 110, 10002) of a 5.9 year periodicity in measurements of Newton's gravitational constant, $G$, which show a very strong correlation with observed periodic variations in the length of the day. I have used Bayesian model comparison to test this claim compared to other hypotheses that could explain the variation in the $G$ measurements. I have used the data from the initial claim, and from an updated set of compiled $G$ measurements that more accurately reflect the experimental dates, and find that a model containing an additional unknown Gaussian noise component is hugely favoured, by factors of $\gtrsim e^{30}$, over two models allowing for a sinusoidal component.

gr-qc↗

arXiv2015

Upper Limit to the Transverse to Longitudinal Motion Coupling of a Waveguide Mirror

Waveguide mirrors possess nano-structured surfaces which can potentially provide a significant reduction in thermal noise over conventional dielectric mirrors. To avoid introducing additional phase noise from motion of the mirror transverse to the reflected light, however, they must possess a mechanism to suppress the phase effects associated with the incident light translating across the nano-structured surface. It has been shown that with carefully chosen parameters this additional phase noise can be suppressed. We present an experimental measurement of the coupling of transverse to longitudinal displacements in such a waveguide mirror designed for 1064 nm light. We place an upper limit on the level of measured transverse to longitudinal coupling of one part in seventeen thousand with 95% confidence, representing a significant improvement over a previously measured grating mirror.

astro-ph.IM↗

arXiv2014

A Bayesian method for detecting stellar flares

We present a Bayesian-odds-ratio-based algorithm for detecting stellar flares in light curve data. We assume flares are described by a model in which there is a rapid rise with a half-Gaussian profile, followed by an exponential decay. Our signal model also contains a polynomial background model. This is required to fit underlying light curve variations that are expected in the data, which could otherwise partially mimic a flare. We characterise the false alarm probability and efficiency of this method and compare it with a simpler thresholding method based on that used in Walkowicz et al (2011). We find our method has a significant increase in detection efficiency for low signal-to-noise ratio (S/N) flares. For a conservative false alarm probability our method can detect 95% of flares with S/N less than ~20, as compared to S/N of ~25 for the simpler method. As an example we have applied our method to a selection of stars in Kepler Quarter 1 data. The method finds 687 flaring stars with a total of 1873 flares after vetos have been applied. For these flares we have characterised their durations and and signal-to-noise ratios.

astro-ph.SR↗

arXiv2014

Advanced technologies for future ground-based, laser-interferometric gravitational wave detectors

We present a review of modern optical techniques being used and developed for the field of gravitational wave detection. We describe the current state-of-the-art of gravitational waves detector technologies with regard to optical layouts, suspensions and test masses. We discuss the dominant sources and noise in each of these subsystems and the developments that will help mitigate them for future generations of detectors. We very briefly summarise some of the novel astrophysics that will be possible with these upgraded detectors.

astro-ph.IM↗

arXiv2012

A new code for parameter estimation in searches for gravitational waves from known pulsars

We describe the consistency testing of a new code for gravitational wave signal parameter estimation in known pulsar searches. The code uses an implementation of nested sampling to explore the likelihood volume. Using fake signals and simulated noise we compare this to a previous code that calculated the signal parameter posterior distributions on both a grid and using a crude Markov chain Monte Carlo (MCMC) method. We define a new parameterisation of two orientation angles of neutron stars used in the signal model (the initial phase and polarisation angle), which breaks a degeneracy between them and allows more efficient exploration of those parameters. Finally, we briefly describe potential areas for further study and the uses of this code in the future.

astro-ph.HE↗

arXiv2008

Searching for gravitational waves from Cassiopeia A with LIGO

We describe a search underway for periodic gravitational waves from the central compact object in the supernova remnant Cassiopeia A. The object is the youngest likely neutron star in the Galaxy. Its position is well known, but the object does not pulse in any electromagnetic radiation band and thus presents a challenge in searching the parameter space of frequency and frequency derivatives. We estimate that a fully coherent search can, with a reasonable amount of time on a computing cluster, achieve a sensitivity at which it is theoretically possible (though not likely) to observe a signal even with the initial LIGO noise spectrum. Cassiopeia A is only the second object after the Crab pulsar for which this is true. The search method described here can also obtain interesting results for similar objects with current LIGO sensitivity.

gr-qc↗

arXiv2007

An Evidence Based Search Method For Gravitational Waves From Neutron Star Ring-downs

The excitation of quadrupolar quasi-normal modes in a neutron star leads to the emission of a short, distinctive, burst of gravitational radiation in the form of a decaying sinusoid or `ring-down'. We present a Bayesian analysis method which incorporates relevant prior information about the source and known instrumental artifacts to conduct a robust search for the gravitational wave emission associated with pulsar glitches and soft $γ$-ray repeater flares. Instrumental transients are modelled as sine-Gaussian and their evidence, or marginal likelihood, is compared with that of Gaussian white noise and ring-downs via the `odds-ratio'. Tests using simulated data with a noise spectral density similar to the LIGO interferometer around 1 kHz yield 50% detection efficiency and 1% false alarm probability for ring-down signals with signal-to-noise ratio $ρ=5.2$. For a source at 15 kpc this requires an energy of $1.3\times 10^{-5}M_{\astrosun}c^2$ to be emitted as gravitational waves.

gr-qc↗

arXiv2007

Report on the first round of the Mock LISA Data Challenges

The Mock LISA Data Challenges (MLDCs) have the dual purpose of fostering the development of LISA data analysis tools and capabilities, and demonstrating the technical readiness already achieved by the gravitational-wave community in distilling a rich science payoff from the LISA data output. The first round of MLDCs has just been completed: nine data sets containing simulated gravitational wave signals produced either by galactic binaries or massive black hole binaries embedded in simulated LISA instrumental noise were released in June 2006 with deadline for submission of results at the beginning of December 2006. Ten groups have participated in this first round of challenges. Here we describe the challenges, summarise the results, and provide a first critical assessment of the entries.

gr-qc↗