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Searches and Analysis

Searching for Inspiraling Compact Binaries

Inspiraling compact binaries consisting of black holes and/or neutron stars are one of the most promising sources of gravitational radiation for the first generation of gravitational wave detectors, such as LIGO. On time scales of 107 years, a compact binary system loses energy by emitting gravitational waves causing its components to spiral together. As the orbit shrinks, it circularizes and the period decreases. With LIGO, we search for the gravitational waves that would be emitted during the final tens of seconds of this inspiral. The stars orbit hundreds of times per second at separations of tens of km before plunging together. The first generation of detectors can observe binary neutron star systems with a reasonable signal-to-noise ratio to about 20 Mpc, with an estimated rate which could be as high as one every 1.5 years, although the true rate is unknown and could be lower.

The coalescence of neutron star--black hole (NS-BH) binaries is believed to be the most promising progenitor of short-hard gamma ray bursts. The direct detection of gravitational waves associated with a GRB would provide compelling evidence for this hypothesis, solving the long-standing mystery of the short-hard GRB origin. The gravitational waves from such systems are likely to be complex, however. Coupling of the orbital angular momentum of a NS-BH binary to the spin of the black hole causes the binary to precess. The resulting modulation of the waveform presents significant challenges for detection, increasing the dimension of the waveform parameter space by an order of magnitude.

The LSC/Virgo Compact Binary Coalescence Group is responsible for searching for the gravitational waves produced by inspiral sources using matched-filter techniques. Members of the Syracuse group collaborate with other members of the Compact Binary Coalescence Group to develop, implement and use algorithms sift through gravitational-wave detector noise for inspiral signals, and to study the relativity and astrophysics that can be obtained from a detection. We are particularly interested in developing search techniques for the spinning binaries described above, as well contributing to the binary neutron star and binary black hole searches.

Picture at right and above, along with gravitational waves, it is expected that a powerful burst of gamma rays is emitted when two binar neutron stars merge.  Dectection of such a gamma ray burst coincident with the detection of gravitational  waves from an inspiral would confirm this hypothesis.


Searching for Unmodeled Gravitational Wave Bursts

In the search for gravitational waves, we need to be able to find brief burst-like waves, even if we don't have a good idea of their waveform. For sources such as supernovae, we don't have a good enough understanding of the physics to know in detail what the waveform will look like. This requires the development of special data analysis methods that don't depend on the classic technique of "matched filtering." Once we have data analysis methods for this purpose, they also serve as a hedge against surprises that might mess up other matched filter searches.

Within the LIGO and Virgo collaborations, the job of looking for burst-like signals and using non-matched-filter methods is the job of the Burst Group. At Syracuse, we contribute to the burst search in several ways. One way is in the development of strategies to define "vetoes", indications from environmental sensors or internal diagnostic measurements that the interferometer was disturbed at a particular time, in such a way that a false signal may have developed.

Picture at left and above, gravitational waves from supernova, such as SN 1604 shown here, are possible sources for the Burst Search (Credit:  HST/NASA/ESA).