Gravitational wave radiometry: Mapping a stochastic gravitational wave background
- Inter-University Centre for Astronomy and Astrophysics, Post Bag 4, Ganeshkhind, Pune 411007 (India)
- LIGO Laboratory, California Institute of Technology, MS 18-34, Pasadena, California 91125 (United States)
- Department of Physics, Washington State University, Pullman, Washington 99164-2814 (United States)
The problem of the detection and mapping of a stochastic gravitational wave background (SGWB), either cosmological or astrophysical, bears a strong semblance to the analysis of the cosmic microwave background (CMB) anisotropy and polarization, which too is a stochastic field, statistically described in terms of its correlation properties. An astrophysical gravitational wave background (AGWB) will likely arise from an incoherent superposition of unmodelled and/or unresolved sources and cosmological gravitational wave backgrounds (CGWB) are also predicted in certain scenarios. The basic statistic we use is the cross correlation between the data from a pair of detectors. In order to ''point'' the pair of detectors at different locations one must suitably delay the signal by the amount it takes for the gravitational waves (GW) to travel to both detectors corresponding to a source direction. Then the raw (observed) sky map of the SGWB is the signal convolved with a beam response function that varies with location in the sky. We first present a thorough analytic understanding of the structure of the beam response function using an analytic approach employing the stationary phase approximation. The true sky map is obtained by numerically deconvolving the beam function in the integral (convolution) equation. We adopt the maximum likelihood framework to estimate the true sky map using the conjugate gradient method that has been successfully used in the broadly similar, well-studied CMB map-making problem. We numerically implement and demonstrate the method on signal generated by simulated (unpolarized) SGWB for the GW radiometer consisting of the LIGO pair of detectors at Hanford and Livingston. We include 'realistic' additive Gaussian noise in each data stream based on the LIGO-I noise power spectral density. The extension of the method to multiple baselines and polarized GWB is outlined. In the near future the network of GW detectors, including the Advanced LIGO and Virgo detectors that will be sensitive to sources within a thousand times larger spatial volume, could provide promising data sets for GW radiometry.
- OSTI ID:
- 21039078
- Journal Information:
- Physical Review. D, Particles Fields, Vol. 77, Issue 4; Other Information: DOI: 10.1103/PhysRevD.77.042002; (c) 2008 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 0556-2821
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
ANISOTROPY
APPROXIMATIONS
ASTROPHYSICS
COMPUTERIZED SIMULATION
CORRELATIONS
COSMOLOGY
DETECTION
GRAVITATIONAL WAVE DETECTORS
GRAVITATIONAL WAVES
MAPPING
MAXIMUM-LIKELIHOOD FIT
POLARIZATION
RELICT RADIATION
RESPONSE FUNCTIONS
SPECTRAL DENSITY
STOCHASTIC PROCESSES