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B.J. Rickett, W.A. Coles (University of California San Diego)
We report a series of observations of the interstellar scintillation of the double pulsar in the band 1700 to 2200 MHz using the Green Bank Telescope. At eight epochs over one year we recorded the dynamic spectrum for one or two binary orbits. From each observation we studied the variation of the scintillation timescale of pulsar A over its orbit and fitted the result with an elliptical model for the spatial correlation of intensity. For this pulsar only three parameters can be fit at each epoch because its inclination is so close to 90 deg (in general five parameters can be fit). We have 5 unknown parameters: the axial ratio and orientation of the ellipse; the center of mass velocity of the binary system; and the spatial scale of the scintillation (in general the inclination is also unknown). The apparent scintillation velocity includes a significant component due to the Earth's orbital velocity. Thus, although we cannot fit all the unknowns at each epoch, we can use the changes in the Earth's orbital velocity over a year to provide extra degrees of freedom. In this way, we can constrain the true center of mass velocity in a known reference frame; the axial ratio and orientation of the scintillation; and the distance to the interstellar scattering layer. In studying the scintillation model we realized that in the general case one cannot unambiguously fit the anisotropy but one can find a lower bound. We applied this to published data for J1141-6545 and found that the scintillation is measurably anisotropic with an axial ratio of at least 1.3. Measurements of annual variation of this source would undoubtedly provide a much tighter estimate of the anisotropy as well as a better estimate of the center of mass velocity.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.