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LIGO Technology Development and Migration

Explore the menu of case study links (left) to view impacts of LIGO technology across the broader science and engineering community.

Technology Type:  Computation and Data Analysis

A New Blind Search Method for Analyzing the Fermi-LAT Data for Gamma-Ray Pulsars

** Contact:  Professor Bruce Allen  
Albert-Einstein-Institut Hannover: Max-Planck-Institut für Gravitationsphysik und Institut für Gravitationsphysik, Leibniz Universität Hannover
      Callinstr. 38 D-30167 Hannover, Germany
      +49-511-762-17148
Adjunct Professor, Physics Department, University of Wisconsin–Milwaukee, Milwaukee, WI 53211, USA

** Working Group:  LIGO Scientific Collaboration Continuous Wave
      Search Group
  

** Funding Agencies:  Max Planck Society and the National Science
      Foundation

** Technology Source:  LIGO Scientific Collaboration (LSC) members
      outside of LIGO Laboratory

[distro]While technology transfer is often thought to flow mainly from the scientific to the commercial or defense realms, there are many instances when technology is transferred between scientific disciplines. This is one such example. Moreover it is a case in which the technology is based not on pieces of metal or glass, but on algorithms.

The LIGO Scientific Collaboration (LSC) data analysis working groups have, for over 10 years, been developing techniques to search through the data streams from the LIGO, VIRGO, and GEO interferometric gravitational-wave detectors. They are on the hunt for gravitational-wave signals from compact binary coalescences, exploding stars, the Big Bang, and spinning neutron stars, to name a few. These signals are rare, weak, and buried under the instrumental noise of the detectors, requiring sophisticated data analysis algorithms and pipelines to identify them.

LSC’s Continuous Wave Search Group searches for coherent, continuous quasi-sinusoidal gravitational-wave signals generated by rapidly spinning neutron stars with slight asymmetries in their shapes. They have developed data analysis pipelines with particularly sophisticated procedures for efficiently searching a large set of data for weak signals from anyplace on the sky and with an unknown and continuously changing frequency.

[sk]In 2009 members of the group began to investigate the possibility of using some of their algorithms, pipelines and infrastructure (including the ATLAS computing system and Einstein@Home), to analyze data from other non-gravitational-wave astrophysical detectors. One of the first sources investigated was gamma-ray pulsars. These are incredibly dense neutron stars that produce short periodic pulses of gamma rays associated with the spin of the star. Even though the pulsars spin many times per second, space-based gamma ray telescopes only detect a gamma ray photon perhaps once in every 100,000 rotations. This may seem very different from the sinusoidal signal detection problem for continuous gravitational waves, but the timing of both signals are similarly affected by the Earth’s orbital motion and spin, and by the gradual deceleration of the neutron star over time. Also in both cases years of data must be included to accrue sufficient signal strength to detect a weak signal over the detector noise. This makes both kinds of searches very sensitive to the location of the source on the sky; and if the source location and pulse period are unknown, both types of searches must be repeated for each sky location and period in a similar way. Computationally, this is a very challenging problem, and one of the innovations made by the LSC members was to devise strategies to maximize the sensitivity of a search given a fixed amount of computational resources.

Members of the LSC Continuous Wave Search Group have collaborated with scientists working on the space-based Fermi gamma ray telescope and with radio pulsar astronomers to apply the methods developed for gravitational wave detection to the detection of gamma-ray pulsars. They applied a slightly modified version of the method to data from the Fermi Large Area Telescope (LAT) and found signals for nine pulsars previously undetected in either gamma-rays or radio in those data. This increased the number of pulsars without radio counterparts discovered in the Fermi LAT data by more than a third, and further discoveries are expected.

References

1.  Discovery of Nine Gamma-Ray Pulsars in Fermi Large Area Telescope Data Using a New Blind Search Method    H.J. Pletsch et al.    The Astrophysics Journal  744:105,  2012 January 10
2.  Exploiting Large-Scale Correlations to Detect Continuous Gravitational Waves  H.J. Pletsch and B. Allen  Physics Review Letters   103, 181102 (2009)

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