IVth School of Astroparticle Physics
May 27th - June 1st, 2013
OHP, Saint Michel l'Observatoire

Gravitational Waves

The search for continuous gravitational waves signals: data analysis techniques, recent results, future prospects

Cristiano PALOMBA
Istituto Nazionale di Fisica Nucleare (INFN) Roma


In this lecture I give an introduction to the search of continuous gravitational wave signals emitted by spinning neutron stars. I describe the search challenge and the fundamentals of the used data analysis methods. Recent results obtained with current detectors and prospects for future detectors are also presented.

  1. Introduction
  2. Signal characterization
    • Expected signal amplitude
    • Doppler modulation, spin-down and relativistic effects
    • Amplitude and phase modulation
  3. Analysis methods
    • Targeted search
    • Blind search
    • Complications with real data
    • Computational issues
  4. Detection, upper limits and their astrophysical interpretation
    • Frequentist approach
    • Bayesian approach
    • Interpretation of upper limits
  5. Link with electromagnetic astronomy
    • Glitches and timing noise
    • Pulsar ephemeris
    • Analogy with gamma-ray pulsar searches
  6. Some recent results
  7. Expectations from advanced detector era and beyond


Continuous signals emitted by spinning neutron stars are among the targets of current and future gravitational wave detectors. Due to the expected weakness of the signals very long integration times, of months to years, are needed in order to increase the signal-to-noise ratio to a detectable level. Two different kinds of search are typically considered: search for signals emitted  by known neutron stars (e.g. pulsars) and blind searches for unknown sources. In the former case the source parameters are often  known with a very high accuracy (thanks to electromagnetic observations) and high sensitivity coherent analysis methods can be applied. In the latter case the parameter space to be explored is huge and hierarchical methods, that reduce the computational  burden at the cost of a relatively small sensitivity loss, have been developed.
In this lecture I will discuss the main features of the expected signals and will present the fundamentals of the data analysis for such kind of sources. The link with the electromagnetic astronomy will be outlined. Even tough no detection has been  obtained until now, present day detector sensitivity is such that some interesting astrophysical constraint can be already established.
In this context, I will show some recent results obtained in the analysis of current data and what are the expectations for future detectors.

  • Gravitational waves from neutron stars: promises and challenges, N. Andersson et al., General Relativity & Gravitation 43, 409 (2011)
  • Searches for continuous gravitational wave signals and stochastic backgrounds in LIGO and Virgo data, C. Palomba,Proceedings of the XLVIth Recontres de Moriond (2011)
  • Gravitational-Wave data analysis. Formalism and sample applications: the Gaussian case, P. Jaranowski & A. Krolak, Living Review of Relativity 15, 4 (2012)


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