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This answer and comments got me thinking. Astrometry 101 tells us that while we can use $\lambda/D$ as an estimator of resolution, if we can assume a point source we can determine the centroid or position to far higher precision.

For example, GAIA's design targets for precision were roughly 7, 20, and 200 micro-arcseconds for visual magnitudes 10, 15, and 20, respectively whereas $\lambda/D$ gives 70,000 x 200,000 micro-arcseconds for its rectangular mirror.

The limitations are both instrumental beyond just the aperture or baseline, and connected to the nature of the signal, and that's were determining the direction of a gravitational wave source is very different than determining the direction of a star's light.

Question: For gravitational waves then, what actually determines the angular uncertainty of the source direction? Does it turn out to be baseline-limited (e.g. $\lambda/D$) or instrument-limited, or limited by the very short-lived and chirped nature of the signal? Or is it something else, perhaps in the modeling and reconstruction of the event itself?

From ligo.caltech.edu's Gravitational-Wave Observatories Across the Globe just for background:

Gravitational-Wave Observatories Across the Globe

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