Gravitational waves found again: here’s how they could whisper the universe’s secrets

The international team of physicists and astronomers responsible for the discovery of gravitational waves back in February has announced the detection of a second strong signal from the depths of space. It is further confirmation that gravitational waves both exist and tell us a whole new story about how the universe came to be the way it is

Digital Preservation and Astronomy: Lessons for funders and the funded

Astronomy looks after its data better than most disciplines, and it is no coincidence that the consensus standard for the archival preservation of all types of digital assets -- the OAIS Reference Model -- emerged originally from the space science community. It is useful to highlight both what is different about astronomy (and indeed about Big Science in general), what could be improved, and what is exemplary, and in the process I will give a brief introduction to the framework of the OAIS model, and its useful conceptual vocabulary. I will illustrate this with a discussion of the spectrum of big-science data management practices from astronomy, through gravitational wave (GW) data, to particle physics.Comment: 4 pages, 1 figure, to appear in proceedings of ADASS XX; corresponds to LIGO document P100017

Binary system delays and timing noise in searches for gravitational waves from known pulsars

The majority of fast millisecond pulsars are in binary systems, so that any periodic signal they emit is modulated by both Doppler and relativistic effects. Here we show how well-established binary models can be used to account for these effects in searches for gravitational waves from known pulsars within binary systems. A seperate issue affecting certain pulsar signals is that of timing noise and we show how this, with particular reference to the Crab pulsar, can be compensated for by using regularly updated timing ephemerides.Comment: 10 pages, 11 figures, accepted by Phys. Rev.

Bayesian estimation of pulsar parameters from gravitational wave data

We present a method of searching for, and parameterizing, signals from known radio pulsars in data from interferometric gravitational wave detectors. This method has been applied to data from the LIGO and GEO 600 detectors to set upper limits on the gravitational wave emission from several radio pulsars. Here we discuss the nature of the signal and the performance of the technique on simulated data. We show how to perform a coherent multiple detector analysis and give some insight in the covariance between the signal parameters.Comment: 9 pages, 6 figures. Accepted to Phys. Rev. D. A few small changes from previous versio

Managing Research Data in Big Science

The project which led to this report was funded by JISC in 2010--2011 as part of its 'Managing Research Data' programme, to examine the way in which Big Science data is managed, and produce any recommendations which may be appropriate. Big science data is different: it comes in large volumes, and it is shared and exploited in ways which may differ from other disciplines. This project has explored these differences using as a case-study Gravitational Wave data generated by the LSC, and has produced recommendations intended to be useful variously to JISC, the funding council (STFC) and the LSC community. In Sect. 1 we define what we mean by 'big science', describe the overall data culture there, laying stress on how it necessarily or contingently differs from other disciplines. In Sect. 2 we discuss the benefits of a formal data-preservation strategy, and the cases for open data and for well-preserved data that follow from that. This leads to our recommendations that, in essence, funders should adopt rather light-touch prescriptions regarding data preservation planning: normal data management practice, in the areas under study, corresponds to notably good practice in most other areas, so that the only change we suggest is to make this planning more formal, which makes it more easily auditable, and more amenable to constructive criticism. In Sect. 3 we briefly discuss the LIGO data management plan, and pull together whatever information is available on the estimation of digital preservation costs. The report is informed, throughout, by the OAIS reference model for an open archive

A Metropolis-Hastings algorithm for extracting periodic gravitational wave signals from laser interferometric detector data

The Markov chain Monte Carlo methods offer practical procedures for detecting signals characterized by a large number of parameters and under conditions of low signal-to-noise ratio. We present a Metropolis-Hastings algorithm capable of inferring the spin and orientation parameters of a neutron star from its periodic gravitational wave signature seen by laser interferometric detector

Searching for gravitational waves from the Crab pulsar - the problem of timing noise

Of the current known pulsars, the Crab pulsar (B0531+21) is one of the most promising sources of gravitational waves. The relatively large timing noise of the Crab causes its phase evolution to depart from a simple spin-down model. This effect needs to be taken in to account when performing time domain searches for the Crab pulsar in order to avoid severely degrading the search efficiency. The Jodrell Bank Crab pulsar ephemeris is examined to see if it can be used for tracking the phase evolution of any gravitational wave signal from the pulsar, and we present a method of heterodyning the data that takes account of the phase wander. The possibility of obtaining physical information about the pulsar from comparisons of the electromagnetically and a gravitationally observed timing noise is discussed. Finally, additional problems caused by pulsar glitches are discussed.Comment: 5 pages, 1 figure, Proceedings of the 5th Amaldi Conference on Gravitational Waves, Pisa, Italy, 6-11 July 200

Disconnected interferometry at 81.5 MHz

Long Baseline Interferometry is a well established technique that enables high angular resolution measurements to be made with a radio interferometer containing independent local oscillators and signal recorders. This Thesis addresses the problems encountered when this technique is applied to low frequency (81.5 MHz) astronomy, and specifically methods of improving its phase stability. The technique is used to reassess existing evidence for the existence of large-scale structure associated with the quasar 3C48, and to give a much better understanding of the structure and behaviour of the supernova remnant Cassiopeia A at low frequencies. Much of the instrumentation used for this work already existed, but in a form unsuitable for measuring phase. The first section of the Thesis shows how these data collection and digital correlator systems could be modified and extended to improve sensitivity and generate true interferometric phase. Two phase calibration schemes are also considered. Firstly, the ‘thin triangle’ method, which uses the closure phase generated by a three-element interferometer to determine the true astronomical phase of a source comprising a single, bright point source and an associated resolvable component. This includes an analysis of how best to determine closure phase when the signal-to-noise ratio on one or more of the baselines is low, and shows techniques based on the ‘triple-product’ method, proposed by Cornwell, to perform best. Secondly, a new method of instrumental stabilisation is introduced and demonstrated, in which the interferometer is calibrated by broadband signals from VHF public broadcast transmitters, which are processed along with the astronomical data. The technique is shown to be capable of removing practically all the instrumental phase drifts usually associated with a long baseline interferometer on baselines up to 100 km. A number of new observations are also presented, mostly made with the stabilised mobile interferometer described above. Firstly of the bright quasar 3C48 to investigate earlier reports of an associated steep-spectrum extended component. These show the importance of considering the effects of confusion in the earlier observations and prompt a critical reassessment of the existing evidence, which is shown to be flawed. Detailed observations of the supernova remnant Cassiopeia A are also presented, with a resolution and sensitivity previously unattained at metre wavelengths. Comparisons with 20 cm VLA data of the same epoch show the remnant to look remarkably similar at the two frequencies, though tentative spectral index measurements indicate that its younger features have slightly steeper spectra than the rest. Furthermore, sensitive observations made on a 128 km baseline show that Cassiopeia A does not contain the steep-spectrum compact component with a flux density of more than 5 Jy reported by many earlier authors. An even deeper search at 408 MHz, this time for pulsed emission from the remnant, puts an upper limit of 80 mJy on the flux density due to any associated pulsar with a period 4 > P > 0.02 sec

Rapid parameter estimation for an all-sky continuous gravitational wave search using conditional varitational auto-encoders

All-sky searches for continuous gravitational waves are generally model dependent and computationally costly to run. By contrast, SOAP is a model-agnostic search that rapidly returns candidate signal tracks in the time-frequency plane. In this work we extend the SOAP search to return broad Bayesian posteriors on the astrophysical parameters of a specific signal model. These constraints drastically reduce the volume of parameter space that any follow-up search needs to explore, so increasing the speed at which candidates can be identified and confirmed. Our method uses a machine learning technique, specifically a conditional variational auto-encoder, and delivers a rapid estimation of the posterior distribution of the four Doppler parameters of a continuous wave signal. It does so without requiring a clear definition of a likelihood function, or being shown any true Bayesian posteriors in training. We demonstrate how the Doppler parameter space volume can be reduced by a factor of $\mathcal{O}(10^{-7})$ for signals of SNR 100

Detecting gravitational radiation from neutron stars using a six-parameter adaptive MCMC method

We present a Markov chain Monte Carlo technique for detecting gravitational radiation from a neutron star in laser interferometer data. The algorithm can estimate up to six unknown parameters of the target, including the rotation frequency and frequency derivative, using reparametrization, delayed rejection and simulated annealing. We highlight how a simple extension of the method, distributed over multiple computer processors, will allow for a search over a narrow frequency band. The ultimate goal of this research is to search for sources at a known locations, but uncertain spin parameters, such as may be found in SN1987A.Comment: Submitted to Classical and Quantum Gravity for GWDAW-8 proceeding